# Why do my spokes keep breaking? - Bike wheel science.



## united4ever (8 Jan 2019)

3 in 3 months! Ridden for 3 years prior with no broken spokes. I get them fixed by lbs within a few days after each one has gone.

Shizuoka hoy 1 bike, Commuting down canal towpath 8 miles each way with paneers with clothes and lunch in them. i weigh 87kgs and haven't put on weight recently.

Anything I should be looking for before just replacing another spoke? is it easy to do for a fairly hands off cyclist who usually uses lbs for much more than puncture or minor tweaks? Should I look at new wheel?


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## Yellow Saddle (9 Jan 2019)

united4ever said:


> 3 in 3 months! Ridden for 3 years prior with no broken spokes. I get them fixed by lbs within a few days after each one has gone.
> 
> Shizuoka hoy 1 bike, Commuting down canal towpath 8 miles each way with paneers with clothes and lunch in them. i weigh 87kgs and haven't put on weight recently.
> 
> Anything I should be looking for before just replacing another spoke? is it easy to do for a fairly hands off cyclist who usually uses lbs for much more than puncture or minor tweaks? Should I look at new wheel?



Unless someone threw a spear into your wheel whilst you were riding, spokes don't break in tension. They break from fatigue - metal fatigue. Metal fatigue is directly related to the number of cycles the wheel undergoes and, the load the wheel receives whilst doing those cycles.

Your spokes are fatigued and because it will be highly unlikely for them all to break at the exact same time, they're breaking one after the other. 

Your wheelbuilder has to replace them all, not just the ones that break.


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## si_c (9 Jan 2019)

united4ever said:


> 3 in 3 months! Ridden for 3 years prior with no broken spokes. I get them fixed by lbs within a few days after each one has gone.
> 
> Shizuoka hoy 1 bike, Commuting down canal towpath 8 miles each way with paneers with clothes and lunch in them. i weigh 87kgs and haven't put on weight recently.
> 
> Anything I should be looking for before just replacing another spoke? is it easy to do for a fairly hands off cyclist who usually uses lbs for much more than puncture or minor tweaks? Should I look at new wheel?



My dynamo front wheel is starting to suffer the same problem, I've had two spokes break in the last month or so, both on the left side and both times whilst braking (disc brakes). I've ordered a full set of replacement spokes, I just need to get around to taking the wheel apart and rebuilding. It's the first one I've built, so it was done poorly. A full set of spokes for a wheel should cost around £30 plus the cost of rebuilding it, which around here is around £20 at an LBS, cheaper than just replacing it.


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## united4ever (9 Jan 2019)

Thanks. Only had the bike a year and only done about 3k miles on it. Would rather it was sorted out once and for all. I bought it from Evans. I may ask the LBS to replace them all then.


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## united4ever (9 Jan 2019)

My LBS have agreed with your consensus...£55 sounds reasonable to me so may go with that:

"If you keep getting broken spokes there's a few issues that could be causing it. If the wheel is old then the spokes may be reaching the natural end of their lifespan and will continue to break. A poor quality wheel may de-tension with use and put uneven amounts of stress on spokes causes them to break. Or it may be a case of simply overloading the wheels with excess baggage on the bike. It may be time to replace the wheel. 

We could do a similar style hybrid wheel for £55 plus £10 to fit if that's the route you'd like to go down."


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## Yellow Saddle (9 Jan 2019)

united4ever said:


> My LBS have agreed with your consensus...£55 sounds reasonable to me so may go with that:
> 
> "If you keep getting broken spokes there's a few issues that could be causing it. If the wheel is old then the spokes may be reaching the natural end of their lifespan and will continue to break. A poor quality wheel may de-tension with use and put uneven amounts of stress on spokes causes them to break. Or it may be a case of simply overloading the wheels with excess baggage on the bike. It may be time to replace the wheel.
> 
> We could do a similar style hybrid wheel for £55 plus £10 to fit if that's the route you'd like to go down."



Who's quote is that? That person does not understand the mechanics of wire spoked wheels. Find a real wheelbuilder.


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## mickle (9 Jan 2019)

Loose spokes move microscopically with every pedal stroke. Moving spokes fatigue or literally wear out if the movement is between, for example, a steel hub flange and a spoke elbow.

Cheap spokes tend to die sooner. 

So run tight wheels, or use decent spokes. Or both.


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## Yellow Saddle (9 Jan 2019)

mickle said:


> Loose spokes move microscopically with every pedal stroke. Moving spokes fatigue or literally wear out if the movement is between, for example, a steel hub flange and a spoke elbow.
> 
> Cheap spokes tend to die sooner.
> 
> So run tight wheels, or use decent spokes. Or both.



No. It doesn't work like that. Only the cheap spoke bit is true.


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## mickle (9 Jan 2019)

Yellow Saddle said:


> No. It doesn't work like that. Only the cheap spoke bit is true.


How does a pice of material fatigue if there's no movement?


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## united4ever (9 Jan 2019)

Yellow Saddle said:


> Who's quote is that? That person does not understand the mechanics of wire spoked wheels. Find a real wheelbuilder.



Revolve Manchester

https://www.revolvemcr.com/

Anyone know a decent one in Manchester/Trafford/Salford Quays area?


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## Yellow Saddle (9 Jan 2019)

mickle said:


> How does a pice of material fatigue if there's no movement?



Where do you propose that movement to happen so that it "literally" wears the spoke? Can you show photos of such wear?


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## rogerzilla (9 Jan 2019)

They're bad wheels: either built with poor quality spokes or (more likely) badly built - insufficiently tight, not stress-relieved, poor spoke-rim angle or even laced the wrong way round, with spokes from the LH rim holes into the RH flange. Not many bike shops build great wheels; they don't have the time to do the best job for what you'd be willing to pay, probably £25 a wheel labour, so ask around for recommendations. Try to get DT spokes; Sapim are also good but I don't find them quite as easy to build with (consistency in length, probably).

The well-known specialist builders insist on choosing the components as they know they can get good results in an acceptable time when all the unknowns are eliminated.


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## united4ever (9 Jan 2019)

rogerzilla said:


> They're bad wheels: either built with poor quality spokes or (more likely) badly built - insufficiently tight, not stress-relieved, poor spoke-rim angle or even laced the wrong way round, with spokes from the LH rim holes into the RH flange. Not many bike shops build great wheels; they don't have the time to do the best job for what you'd be willing to pay, probably £25 a wheel labour, so ask around for recommendations. Try to get DT spokes; Sapim are also good but I don't find them quite as easy to build with (consistency in length, probably).
> 
> The well-known specialist builders insist on choosing the components as they know they can get good results in an acceptable time when all the unknowns are eliminated.



This makes sense...I had the identical bike (until it got wrecked in an accident) which seemed to have been built better somehow.....the replacement fells less harmonious somehow and I had no broken spokes with last bike....though that was the same quality parts so maybe just got lucky and was unlucky to get a badly put together one this time. Suppose you get what you pay for.


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## DCBassman (9 Jan 2019)

@mickle 
"How does a pice of material fatigue if there's no movement?"


I'm no expert, but repeated tension/compression cycles? That doesn't imply movement.


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## Yellow Saddle (9 Jan 2019)

mickle said:


> Loose spokes move microscopically with every pedal stroke. Moving spokes fatigue or literally wear out if the movement is between, for example, a steel hub flange and a spoke elbow.
> 
> Cheap spokes tend to die sooner.
> 
> So run tight wheels, or use decent spokes. Or both.



*"Loose spokes move microscopically with every pedal stroke."*


There is no relative movement between spokes and spokes, or spokes and other wheel parts during a wheel's use that's enough to cause any sort of wear in a spoke. Wear implies loss of material, of which there is none.

Spokes do flex during wheel revolutions and they flex at the bottom of the wheel in the load affected zone, which is an area between the road and rim. Even then, they only flex by becoming SHORTER. This change in length is indeed microscopic and it is taken up evenly along the entire length of the spoke. Therefore the change in length per mm of spoke length is indeed microscopic. For all intends and purposes the relative movement between hub and spoke, where the spoke touches the hub flange is thus zero. We know this because there is no visible rouge in that area when you disassemble a wheel, nor is there ever any signs of material loss on the spoke itself. The hub flexes with the spoke, reducing relative movement between the two.

Steel hubs with sharp edges do indeed cause more spoke breakages but this is not because of wear, but because of conditions that exacerbates metal fatigue. An aluminium hub, being softer than the spoke, changes shape to accommodate the spoke elbow. This smearing creates a larger contact area and softer bend in the spoke, which reduces work hardening and subsequently, metal fatigue in the spoke. Steel hubs don't, causing a very sharp transition at the spoke elbow.

Flex is not movement. 

Spokes flex when just rolling along and additionally with each pedal stroke. Flex from the latter is confided to rear wheels and mostly the right hand spokes only and, only every second one on the right hand side. This flex is small since even a strong launch to sprint only increases the spoke tension in those spokes by less than 5% It is less than the flex induced by mere rolling.

*"Moving spokes fatigue or literally wear out if the movement is between, for example, a steel hub flange and a spoke elbow"*

Movement is not flex. A spoke that's moving is one that's rattling away in the wheel because it has no tension. Such a spoke experiences no forces which cause metal fatigue. As soon as a spoke has some modicum of tension, it will flex as described above and start to fatigue. The rate of fatigue is irrelevant whether the spokes are high tensioned or just-just tensioned enough to keep the wheel together.

I've dealt with the topic of wear. It implies relative movement, abrasion and loss of material. That doesn't happen. 

*"Cheap spokes tend to die sooner."
*
Price is not a reliable indicated of poor spokes, but it has bearing. It costs more to make a double-butted spoke than a straight-gauge spoke and therefore it should cost more. But a double-butted spoke from a SAPIM box or a double-butted spoke from a Campagnolo catalogue are exactly the same spoke, although the price is hugely different. I'm sure you know this but someone else may not.

Good spokes are made from de-gassed, 18/8, cold-forged stainless steel. Rubbish spokes are made from high-tensile steel and then galvanised.
Budget spokes are made from the same material as above, but not butted (drawn) and thus don't receive as much of the benefitical cold forging. But non-butted bit of the spoke, i.e. the thin shank, flexes more than the thick bits at either end. This reduces the strain on those bits and hence, inputs less metal fatigue in those critical parts. Metal fatigue is not as prevalent in the thin, flexible central shank even though it flexes more than the thicker parts.

However, an expensive spoke still needs one bit of material treatment to make it long-lasting and that treatment is stress relieving. It is done by the builder after the build. Unfortunately the spoke company can't build it in, it has to be done after the wheel is finished. Most builders don't have a clue about this, hence the poor wheels we see.

*"So run tight wheels, or use decent spokes. Or both."*

For long spoke life the wheels don't have to be tight. I explained why in the text above. Tight is good however, because it prevents nipples coming loose and wheels losing trueness. Very tight is even better, but it has nothing to do with spoke life. Uneven tension also has nothing to do with spoke life but you don't want such a wheel 'cause it wobbles.


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## PatrickPending (9 Jan 2019)

Whenever this happened to me (and its not for a long time) I've had a wheelbuilder re-build the wheel using good quality stainless steel spokes. I'd advise this course rather than a new machine built wheel....


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## DCBassman (9 Jan 2019)

Dogtrousers said:


> I love these threads. I never understand them, and they just serve to persuade me that I should never, ever, touch a spoke nipple because my wheel will probably come unravelled, like a piece of knitting.
> 
> But I love them nonetheless.


Agreed!


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## mickle (9 Jan 2019)

Yellow Saddle said:


> *"Loose spokes move microscopically with every pedal stroke."*
> 
> 
> There is no relative movement between spokes and spokes, or spokes and other wheel parts during a wheel's use that's enough to cause any sort of wear in a spoke. Wear implies loss of material, of which there is none.
> ...



I love you Yellow Saddle.


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## Old jon (9 Jan 2019)

Flex, English word, US dictionary definition. Dunno how Newton would have defined it.

*Definition of flex *
(Entry 1 of 3)

transitive verb

1 *: *to bend especially repeatedly

2a *: *to move muscles so as to cause flexion of (a joint)

b *: *to move or tense (a muscle) by contraction

3 *: *use, demonstrate flexing her skills as a singer

intransitive verb

*: *bend


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## Yellow Saddle (9 Jan 2019)

Old jon said:


> Flex, English word, US dictionary definition. Dunno how Newton would have defined it.
> 
> *Definition of flex *
> (Entry 1 of 3)
> ...



I agree with you but sometimes I have to simplify in order to keep my audience, and there's no slight intended to my audience. They are a mix and I want them all to have a better understanding of this complex but fascinating topic. The flex that happens with wheel use is elastic deformation aka stretching and compression of the spokes and true flex in the rims. It just isn't as elegant, but, you are of course right. As soon as I use the C word (compressing) in these explanations, it opens a can of worms and starts WW III. If you search under my name for "in compression" and "in tension" you'll see what I mean. This topic repeats every 100 days or so and I prune a bit here and shortcut a bit there each time.


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## Ajax Bay (10 Jan 2019)

Yellow Saddle said:


> The flex that happens with wheel use is elastic deformation aka stretching and compression of the spokes and true flex in the rims. It just isn't as elegant, but, you are of course right. As soon as I use the C word (compressing) in these explanations, it opens a can of worms and starts WW III. If you search under my name for "in compression" and "in tension" you'll see what I mean. This topic repeats every 100 days or so


Well don't use the 'C' word then. Spokes remain in tension unless they are loose (tension = 0N) so they cycle from high tension (normal static ?1000+N) to a lower tension (ie they are stretched less (the lowest spokes in a weight-bearing rolling wheel)). "elastic deformation aka change in tension of each spoke, moderated by true flex in the rims"? A spoke in compression would poke its nipple up and through the rim tape rather quickly, probably with flattening results. I have not experimented to see whether a puncture results - to do so would be nugatory as there is no mechanism other than complete wheel/rim failure which would force a nipple thus. Single rifleman minor skirmish, not WWIII, to deter casual use of the 'C' word.


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## rogerzilla (10 Jan 2019)

Jobst Brandt also talked about the wheel "standing" on its lowest spokes (equating a reduction in tension with compression). It's annoyed a lot of people over the years. He was correct but his choice of words didn't help much.


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## Yellow Saddle (10 Jan 2019)

Ajax Bay said:


> Well don't use the 'C' word then. Spokes remain in tension unless they are loose (tension = 0N) so they cycle from high tension (normal static ?1000+N) to a lower tension (ie they are stretched less (the lowest spokes in a weight-bearing rolling wheel)). "elastic deformation aka change in tension of each spoke, moderated by true flex in the rims"? A spoke in compression would poke its nipple up and through the rim tape rather quickly, probably with flattening results. I have not experimented to see whether a puncture results - to do so would be nugatory as there is no mechanism other than complete wheel/rim failure which would force a nipple thus. Single rifleman minor skirmish, not WWIII, to deter casual use of the 'C' word.


Compression as a concept is important and I'll continue using it. When a wheel cycles, the load affected zone undergoes compression, which leads to a reduction of tension in the spoke. I don't think I've ever explained it to mean anything other that what I've just said. Seen from another angle. When a bike is loaded, there is a compressive force between the hub and road and thus the hub stands on the bottom spokes. There is no other way to state that fact. Compression is important.


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## Levo-Lon (10 Jan 2019)

I usually find the word Alex and Superstar and wheel in the same sentence = a odd snapped spoke.

All my quality wheels seem to stay straight and true.
Capagnolo Mavic and DT Swiss ..DT suffer with shyte bearings but fine when you bin the plastic ones and fit good uns


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## Ajax Bay (10 Jan 2019)

Yellow Saddle said:


> Seen from another angle. When a bike is loaded, there is a compressive force between the hub and road and thus the hub stands on the bottom spokes.


With all due respect, no there isn't and no it doesn't. Let me explain (to use your vernacular) and offer you a view "from another angle".
When a bike is loaded (front wheel for ease of visualisation) a downwards force is exerted on the fork (which is in compression). That downwards force is balanced by an upwards force from the hub. The latter force is exerted on the hub by a balance of the radial positive forces from all the spokes. All the spokes are in tension and the force they're exerting is radial in all cases (they 'pull' away from the hub). At the outer end of every spoke is the rim and the rim exerts a force on every spoke equal (obv) to the tension in the spoke. The rim is in compression, all the time. The contact area of the tyre experiences a 'normal' (ie vertical) force from the road - this force is equal to the load borne by the wheel (referred to in Line 1 above). As you sometimes suggest to others, draw yourself a diagram and mark in the forces and why not label each item which is 'in compression'.
Besides the rim (and the axle with a QR providing the compression) I cannot think of an element of the wheel in compression. Maybe you can (leave the tyre out of it, I suggest).
Isn't the wheel a marvelous invention?


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## Yellow Saddle (10 Jan 2019)

Ajax Bay said:


> With all due respect, no there isn't and no it doesn't. Let me explain (to use your vernacular) and offer you a view "from another angle".
> When a bike is loaded (front wheel for ease of visualisation) a downwards force is exerted on the fork (which is in compression). That downwards force is balanced by an upwards force from the hub. The latter force is exerted on the hub by a balance of the radial positive forces from all the spokes. All the spokes are in tension and the force they're exerting is radial in all cases (they 'pull' away from the hub). At the outer end of every spoke is the rim and the rim exerts a force on every spoke equal (obv) to the tension in the spoke. The rim is in compression, all the time. The contact area of the tyre experiences a 'normal' (ie vertical) force from the road - this force is equal to the load borne by the wheel (referred to in Line 1 above). As you sometimes suggest to others, draw yourself a diagram and mark in the forces and why not label each item which is 'in compression'.
> Besides the rim (and the axle with a QR providing the compression) I cannot think of an element of the wheel in compression. Maybe you can (leave the tyre out of it, I suggest).
> Isn't the wheel a marvelous invention?



Every ounce you put onto the bike is felt by the road. There is a compressive force between road and bike. Put a bathroom scale under each wheel and you'll see.

The only spokes that interact to transmit that net downward force are the ones in the load affected zone, i.e the two or three right at the bottom. The other radial forces in the other spokes play no role in transmitting the bike's weight down to the road. None. They do play a role in keeping the wheel in one piece, but that they do equally when the wheel is held in your hand and touches nothing.

None of the spokes go into compression and no matter how many times you say I said it, I don't and have not. Those spokes receive a compressive force that does not exceed their tension.


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## Ajax Bay (10 Jan 2019)

"Every ounce you put onto the bike is felt by the road." Yes
"There is a compressive force between road and bike." Like the compressive force in the sole of a worn shoe (ETA: ie a shoe which is being worn). Difference is that the wheel is a structure so saying that "there is a compressive force between road and bike" lacks meaning/utility.

"The only spokes that interact to transmit that net downward force are the ones in the load affected zone, i.e the two or three right at the bottom." Depends what you want "interact" to mean. I agree that they're the ones in which tension reduces most, which means they pull down on the hub less than when the wheel is unloaded.
"The other radial forces in the other spokes play no role in transmitting the bike's weight down to the road. None."
Sorry, I have difficulty with that. The hub is 'hanging' on the spokes above it and the upwards force it has to exert on the fork drop outs is because the lower spokes have reduced the amount they are pulling down.
"They [the other spokes] do play a role in keeping the wheel in one piece, but that they do equally when the wheel is held in your hand and touches nothing."
Agreed with the observation that all the spokes (including the lower ones) "play a role in keeping the wheel in one piece" both unloaded and loaded.
"None of the spokes go into compression and no matter how many times you say I said it, I don't and have not."
Apologies if I have suggested that you have said "spokes go into compression". I have tried to find where I have put those words 'into your mouth' but with no success.
"Those spokes receive a compressive force that does not exceed their tension." The lower spokes just experience a cyclical lower tension - the force exerted on a lower spoke by the rim lessens and results in a lower tensile force. This means that the resultant force (the result of all the spokes pulling on the hub at various tensions) on the hub is up (ie operates vertically upwards through the drop outs and is equal to the weight on the wheel).
I think we agree what happens but I think your use of certain terms (like compression, compressive and 'stands') clouds rather than provides the clarity needed for "a better understanding of this complex but fascinating topic".
Draw a diagram.
And a few quotes which show you're keen that others draw diagrams:


Yellow Saddle said:


> A force diagram will take you 30 seconds to do. I'll wait until after the weekend. Pardon my cynicism but I've been here before.





Yellow Saddle said:


> Draw a force diagram and you'll see that your scenario is implausible.


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## Yellow Saddle (10 Jan 2019)

OK, my force diagram is on its way. I'd like you to do one too please. Then we can compare. Hang in there.


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## Ajax Bay (10 Jan 2019)

Yellow Saddle said:


> Hang in there.


Will do. That's what my load bearing hubs are doing.


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## Yellow Saddle (10 Jan 2019)

Here is the data:
1) The fork is loaded with a force of 60. Ignore units, I've kept all units the same, so it doesn't matter.
2) This wheel has 11 spokes. When the wheel is unloaded, each spoke has a tension of 100.
3) The flat bit at the bottom is the Load Affected Zone (LAZ henceforth). There are three spokes in the load affected zone. Because of the load on the hub, the tension in those thee spokes is reduced. The total reduction equals the load on the hub. Therefore the tension in each one of those is now only 80. 100-80 =20. 3 x 20 = 60, which equals the load.

Ignore the fact that the three bottom spokes are all in equal tension. In reality it the middle one would have the lowest tension and then those straddling it a bit more etc etc. It complicates the basic explanation. We can go into how that varies at a later stage.

The system is in equilibrium and conserves Newton's laws.


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## Yellow Saddle (10 Jan 2019)

Ajax Bay said:


> "There is a compressive force between road and bike." Like the compressive force in the sole of a worn shoe. Difference is that the wheel is a structure so saying that "there is a compressive force between road and bike" lacks meaning/utility.



I'm not sure what worn shoe or structure has to do with it. I don't get your argument here at all.



Ajax Bay said:


> "The only spokes that interact to transmit that net downward force are the ones in the load affected zone, i.e the two or three right at the bottom." Depends what you want "interact" to mean. I agree that they're the ones in which tension reduces most, which means they pull down on the hub less than when the wheel is unloaded.



Interact means that they act in a way to support the load. That way is to reduce in tension. None of the other spokes have anything to do with the load, they do exactly what they do as when the wheel is unloaded.



Ajax Bay said:


> "The other radial forces in the other spokes play no role in transmitting the bike's weight down to the road. None."
> Sorry, I have difficulty with that. The hub is 'hanging' on the spokes above it and the upwards force it has to exert on the fork drop outs is because the lower spokes have reduced the amount they are pulling down.



No the hub does not hang on the top spokes. That implies an increase in tension, which doesn't happen. An analogy is to look at a car wheel and tyre. Only the bottom squashes down, the top doesn't somehow become fatter/elongate because the rim is hanging on it.

To get your head around it, remove your front wheel and hold it by the axle, vertically, with two hands, each one side of the wheel. Push the wheel down on the floor by the axle. Now imagine your "hanging" hub. Now, pick up the wheel, turn it horizontally and do the same as before, but push against a wall. What happened to the "hanging" hub.

To prove this experimentally, find two friends to help you. Sit on the bike and have one friend hold you upright. Have the other pluck the bottom spoke and listen to the tone. Unload the bike and listen again. Now sit again and pluck the top spoke. Unload and pluck again. You'll notice that the top tone never changes but the bottom one goes down in frequency when the bike is loaded.



Ajax Bay said:


> The lower spokes just experience a cyclical lower tension - the force exerted on a lower spoke by the rim lessens and results in a lower tensile force. This means that the resultant force (the result of all the spokes pulling on the hub at various tensions) on the hub is up (ie operates vertically upwards through the drop outs and is equal to the weight on the wheel).



Please rephrase, I can't comprehend.



Ajax Bay said:


> I think we agree what happens but I think your use of certain terms (like compression, compressive and 'stands') clouds rather than provides the clarity needed for "a better understanding of this complex but fascinating topic".



That's not my problem. I've explained my meaning of those terms and so far no-one has come up with more appropriate ones. Those are exactly the same terms used in the literature on the topic and accepted by those who understand the concept.


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## Ming the Merciless (10 Jan 2019)

Of the course the tension of the spokes various as the wheel turns. It is nonsense to suggest only when spokes are at the bottom do they change tension. To suggest that the upwards facing spokes play no role in supporting the weight of bike and rider is absurd.


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## Yellow Saddle (10 Jan 2019)

YukonBoy said:


> Of the course the tension of the spokes various as the wheel turns. It is nonsense to suggest only when spokes are at the bottom do they change tension. To suggest that the upwards facing spokes play no role in supporting the weight of bike and rider is absurd.


We ignore the fact that the wheel turns because the only effect that it has is that it alternates the spokes where things happen. A static wheel is an accurate and easy model to work with.

You seem to have a different model for load support. Please feel free to modify my diagram and put figures to what you think happens to the tension.


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## Ming the Merciless (10 Jan 2019)

Well for a start a spike pokes through a hole in the rim and the only thing beyond that is rim tape and a tyre or tube. Neither of which provide support. The spoke does not connect with a so,I'd surface to help it provide load support against a force pushing it towards the tyre.


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## Ajax Bay (10 Jan 2019)

Thank you for the force diagram, @Yellow Saddle , spookily like the one I sketched on paper before being diverted to children taxiing and supper etc. I will attempt to transfer mine to an electronic medium (my application consultant came home ill from school, so ill he even agreed to leave his phone in my care while he went to recuperate in bed (I can see the 'too ill to go to school' card being prepared)).
I went for a load of 500N (eg a 50kg wt load - typical load on a front wheel) and an individual spoke tension at 1000N (a figure I know you have quoted before) except the 2 lower spokes (of 8) at less tension. Resolving vertically each of those two spokes drop to a tension of 730N.
TL = 1/2 (500/cos(22.5deg))
Given up on 'Paint'. Here's a photo:







YukonBoy said:


> Of the course the tension of the spokes various as the wheel turns. It is nonsense to suggest only when spokes are at the bottom do they change tension. To suggest that the upwards facing spokes play no role in supporting the weight of bike and rider is absurd.


I think we all agree that the tension of each spoke varies as the wheel turns. But for the force analysis it's sufficient to consider a static loaded wheel. I seek to persuade YS that the upper spokes, albeit at no more tension than when the wheel is unloaded, provide the surplus force (via the hub) needed to support the load exerted by the fork. Disregarding the spokes other than the top 2 and the bottom 2, this surplus is the force (on the hub) up from the two upper spokes minus the pull down of the two lower spokes.


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## FishFright (10 Jan 2019)

I've always thought that the bike 'hangs' from the spokes above the hubs rather than sits on top of the spokes below the hubs.


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## Ming the Merciless (10 Jan 2019)

The lower spokes in the diagram do not contact the road. Nor do the support the hub above. The only thing stopping the hub moving downwards under the force exerted are the spokes that point upwards which will be under different tensions depending on their angle. If you removed the upper spokes in a static load position the lower spokes would just push through their spoke holes and puncture the inner tube as there is very little to resist the weight of rider and bike weight.


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## Ming the Merciless (10 Jan 2019)

Yellow Saddle said:


> Maybe you should do some research before diving in with the same mistakes which have been made dozens of times before, on this forum. You have not provided a model or a coherent argument.



Yes I have. Pay attention the tension in the spokes is pulling the hub towards the rim in every case. The hub does not move (much) towards any particular part of the rim because it is countered by the tension in the rest of the spokes. The hub does not sit supported on the lower spokes nearest the road surface. Those spokes are not resisting the downward force due to gravity, they have nothing to push against other than rim tape, and that does not offer much resistance compared to the forces in place. It is the spokes pointing upwards that are providing the upwards forces resisting the hub moving downwards under the force of gravity.


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## hobo (11 Jan 2019)

What about the forces involved from the drive side of the rear wheel being applied by the rotational force from the
chain onto the hub?


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## hobo (11 Jan 2019)

Every time iv broke a spoke its been when i have been applying force on to the pedals.
So the torque force breaks the spoke.


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## Yellow Saddle (11 Jan 2019)

hobo said:


> What about the forces involved from the drive side of the rear wheel being applied by the rotational force from the
> chain onto the hub?


Those are particularly interesting.

My art above can't be referenced because driving wheels have to be cross-spoked and that one is radially-spoked.

Nevertheless on a rear wheel where the hub is stiff enough to transmit torque to the side opposite the sprockets, it works like this.
Every second spoke increases in tension and the others decrease in tension. If the tension and reduction were to be exaggerated, then the wheel can be visualised as daisey-shaped. That's because there are "pushing" and "pulling" spokes in such a wheel. The average tension does not change at all, but the tension in individual spokes change by an equivalent positive and negative amount.


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## Yellow Saddle (11 Jan 2019)

Ajax Bay said:


> I think we all agree that the tension of each spoke varies as the wheel turns. and...But for the force analysis it's sufficient to consider a static loaded wheel.


Yes, for now I'm going to ignore the side-chatter that regurgitates stuff we've said before. This includes rotation, spokes lifting off the spoke bed etc. Anyone who wants to understand that or think they've just invented it, can go back in the record and read up on it.

Then, a suggestion. When calculating the reduction in tension at the bottom spokes, we leave out the angular component from the spokes arriving radially. This suggestion is for two reasons.
1) There are paired, parallel spokes in a cross-laced wheel. Typically such as the two spokes either side of the valve and at equal, opposite ends of the wheel. For such a real-world wheel the cosine component for those would have to be disregarded and the adjacent angular spokes then compensated with another angle. We then end up with a different model for each position of the wheel. 
I suggest we treat the LAZ by having a central spoke arriving plumb with the road and two other spokes, either side of it, arriving at X angle. Only these three spokes share the load and we don't attempt to calculate the adjacent spokes' actual share other that attributing an arbritary figure to it. For instance, Central takes 30, the two adjacent ones each take 10, making up a total of 50.

We're not after exact numbers here, just broad concepts.

2) Should you still insist on eliminating the cosine error, then you'd have to know the angle, which is not the same in the load affected zone as it is elsewhere. That's because, as soon as the wheel is loaded, an arc in the circle is converted to a cord, without affecting the length of the arch. In other words, the wheel is deformed by flattening at the bottom and opening up elsewhere. Let's ignore that simply because it does not change the concept.

Then:



Ajax Bay said:


> I seek to persuade YS that the upper spokes, albeit at no more tension than when the wheel is unloaded, provide the surplus force (via the hub) needed to support the load exerted by the fork. Disregarding the spokes other than the top 2 and the bottom 2, this surplus is the force (on the hub) up from the two upper spokes minus the pull down of the two lower spokes.



This seems to be the crux of you differing from me, because, taking into account the exceptions I've suggested above, our models are the same.

What I don't get is "surplus force". Can you show it on the force diagram? I just don't get it.


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## Milkfloat (11 Jan 2019)

I found this the easiest to understand http://hea-www.harvard.edu/~fine/opinions/bikewheel.html
Feel free to pick it apart.


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## Ajax Bay (11 Jan 2019)

hobo said:


> What about the forces involved from the drive side of the rear wheel being applied by the rotational force from the
> chain onto the hub?


https://www.cyclechat.net/threads/broken-spokes-when-to-give-up-on-a-wheel.173282/#post-3500342


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## Milkfloat (11 Jan 2019)

Interestingly at DT Swiss they say that the tension increases on the upper spokes, I think they mean the proportion of load will increase, but not the tension itself, however don't trust me, I make maps for a living, not wheels.

https://www.blog.dtswiss.com/spoke-tension/


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## Yellow Saddle (11 Jan 2019)

Milkfloat said:


> I found this the easiest to understand http://hea-www.harvard.edu/~fine/opinions/bikewheel.html
> Feel free to pick it apart.



It is a nice piece but unfortunately it all falls apart in the end. The precise place where it starts to fail is the last sentence in the third last paragraph. The author understands how the wheel works, but needs to fix up his/her syntax since it only adds to the confusion.


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## Yellow Saddle (11 Jan 2019)

Milkfloat said:


> Interestingly at DT Swiss they say that the tension increases on the upper spokes, I think they mean the proportion of load will increase, but not the tension itself, however don't trust me, I make maps for a living, not wheels.
> 
> https://www.blog.dtswiss.com/spoke-tension/



DT Swiss makes excellent spokes but unfortunately they don't seem to have engineers on their marketing team. I don't trust DT's literature. That company doesn't understand (or perhaps they do but communicates otherwise), the purpose of butted spokes. The company even has an "extra thick spoke" in its catalogue billed as stronger than the others. That smacks of ignorance.


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## Ajax Bay (11 Jan 2019)

Milkfloat said:


> I found this the easiest to understand http://hea-www.harvard.edu/~fine/opinions/bikewheel.html
> Feel free to pick it apart.


Thank you for finding that which I recommend to others to read.
These sections bear commentary:
1) "What's interesting is what happens to the wheel when a load is applied (someone gets on the bike). If you measure the tension in all the spokes, only those spokes in the bottom of the wheel change tension significantly - the tension decreases. In other words, the bottom spokes become more loose, all the other spokes remain unchanged."
I'd prefer the description "the bottom spokes reduce in tension, all the other spokes remain unchanged" as "more loose" to me implies they were "loose" in the first place, but this may be a translation/ntic issue between Oxford and Harvard.
As an aside, "all the other spokes remain unchanged" is not strictly true because the tension in the spokes near the horizontal actually increase slightly (ie above the static tension) to hold the wheel together which would otherwise oval (slightly).
2) "In _mathematical terms_ it is possible to describe the bottom spokes as being in compression. The have less tension than they had before, so if you count the starting (pre-tensioned) state as the zero state, you have put them "in compression". The reason they can support this compression is that the spoke has been pre-tensioned."
That's rather like shifting the area of the graph which has the bottom spokes in compression up from zero (force) to 1000N, on the 'force' axis. "In _mathematical terms_ maybe; but not in _real terms_ (and noone (here) has suggested that the bottom spokes are "in compression". 
3) Otherwise @Yellow Saddle thought this let down the piece:
"Only the upper spokes are actually pulling upwards on the hub. This is why I still say, without any doubt, that *the hub hangs from the upper spokes*. Oddly this does not contradict the following statement, that *the lower spokes play the most dynamic role in supporting the load*."
3a) "Only the upper spokes are actually pulling upwards on the hub." Basically true.
3b) "This is why I still say, without any doubt, that *the hub hangs from the upper spokes*." I don't think "hanging" and "standing" are useful terms to use (and their use seems to provoke unnecessary angst without adding clarity).
3c) "Oddly this does not contradict the following statement, that *the lower spokes play the most dynamic role in supporting the load*." If by "dynamic" [characterized by constant change, activity, or progress] the author means that the lower spoke tensions vary most from the unweighted state then fine, but it's an unusual use of "dynamic" because all spokes in a rolling wheel are 'dynamic' and when considering a static loaded wheel model the spoke tensions are 'static' with different magnitude - again it seems to me the author is seeking to throw a bone to the (standing) dogs.


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## Milkfloat (11 Jan 2019)

Ajax Bay said:


> Thank you for finding that which I recommend to others to read.



Ooops sorry!


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## Ajax Bay (11 Jan 2019)

Yellow Saddle said:


> Then, a suggestion. When calculating the reduction in tension at the bottom spokes, we leave out the angular component from the spokes arriving radially. This suggestion is for two reasons.
> . . . .
> [model] a central spoke arriving plumb with the road and two other spokes, either side of it, arriving at X angle. Only these three spokes share the load
> . . . .
> ...


Our models are essentially the same and lets accept/adopt your 3 lower spokes of relevance at the bottom model, disregarding all but the upper spokes and the lower spokes (3 + 3). Note that I'm content with the model but do not agree with "only these three spokes share the load" (because the albeit reduced tension in the 3 lower spokes is pulling the hub down and not "shar[ing] the load").
The "surplus force" - perhaps an unwise phrase in a 'balanced' system - which I sought to explain is the vertical force that the hub needs to exert on the fork to keep the bike 'up' balancing the gravitational force (40+% of the rider plus bike weight) on the (front) wheel.
The wheel as a structure is 'in compression' load acting down and the ground's 'normal' force acting up. Vector summing (with respect to forces on the hub) the tension in all 6 spokes and "leave out the angular [think you mean horizontal] component from the spokes arriving radially [meaning non-vertically]" there needs to be a 'surplus' vertical force component to resist the fork pushing down.

Forces acting on the fork dropouts
I Fork
I
v
^
I
I Hub

Forces acting on the hub
Upper spokes (all 1000N say)
^
I
I
Iooooooooooooooo^
IoooooooooooooooI
OooHuboooooooooI (500N) Resultant force
I
v
Lower spokes (900/700/900N say)

Notes (agreeing that you/"we're not after exact numbers here"): 16 spoke wheel. 22.5 degrees between each spoke, cos 22.5 is 0.93
Vertical force from 3 upper spokes is 1000 + 2x1000cos 22.5 = 2860N
'Surplus' force required to support load = 500N
Downwards force exerted on hub by the 3 lower spokes = 2860-500=2380N
2380=Tv + 2TLcos22.5 [Tv is tension in vertical spoke, and TL is tension in the two spokes either side of vertical.]
Estimate Tv = 740N and TL = 880N
So as this (model front) wheel rolls, the spoke tension cycle between (slightly over) 1000N (when horizontal) through 880N down to 740N and back up. 
The more spokes in a wheel the less reduction (%) the lowest spoke experiences. Will the magnitude of the cyclical range of tensile force in a spoke be related to fatique life? Probably (intuitively), but I don't know.
The spokes fatique and eventually, when @hobo gives that last push, the rear wheel spoke that happens to be weakest parts. On my ride last week each of my spokes (36 spoke front wheel) went through this cycle (1000N to >800N) over 100,000 times. Last year the spokes in my front wheel which I built it in Jan 18, completed this cycle over 5 million times. I used the original spokes from the fubarred wheel (rim) so I estimate these spokes have completed 20 million cycles with me aboard (plus no idea how many with the first owner on board). Pleased to say no front spokes broken yet.


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## Yellow Saddle (11 Jan 2019)

Ajax Bay said:


> Our models are essentially the same and lets accept/adopt your 3 lower spokes of relevance at the bottom model, disregarding all but the upper spokes and the lower spokes (3 + 3).



Great.



Ajax Bay said:


> Note that I'm content with the model but do not agree with "only these three spokes share the load" (because the albeit reduced tension in the 3 lower spokes is pulling the hub down and not "shar[ing] the load").
> The "surplus force" - perhaps an unwise phrase in a 'balanced' system - which I sought to explain is the vertical force that the hub needs to exert on the fork to keep the bike 'up' balancing the gravitational force (40+% of the rider plus bike weight) on the (front) wheel.


That's not what your diagram shows. Can you show the above in a diagram please. 



Ajax Bay said:


> The wheel as a structure is 'in compression' load acting down and the ground's 'normal' force acting up. Vector summing (with respect to forces on the hub) the tension in all 6 spokes and "leave out the angular [think you mean horizontal] component from the spokes arriving radially [meaning non-vertically]" there needs to be a 'surplus' vertical force component to resist the fork pushing down.



That's where I think you go wrong. Please try and show that in a force diagram. I can't get my head around your ASCII diagram. 


I'm going to resist the distraction about metal fatigue. That's for another day. Let's stick to the forces on a static, loaded wheel for now.


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## Pale Rider (11 Jan 2019)

Apart from comedy physics, has anyone answered the OP?

It's worth replacing a single broken spoke, but if you get a series it's full wheel rebuild time with all new spokes.

That may - or may not - be cheaper/dearer than a new factory built wheel.

Shimano wheels are excellent for someone who just wants the bike to work.


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## Salar (11 Jan 2019)

@Yellow Saddle and @Ajax Bay

I generally agree with your assumptions, funnily enough when you were preparing your diagrams I scribbled one out with the same concept.

The spokes are always in tension.

It reminds me slightly of cross bracing in buildings, guy ropes etc where only one member takes all the force in tension and the other member is redundant.

However my practical mind keeps trying to tell me the upper three spokes take a tensile load of axle load /3 + spoke tension


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## Ajax Bay (11 Jan 2019)

Yellow Saddle said:


> That's not what your diagram [assume the image in AB post 2 pages back] shows. Can you show the above in a diagram please.


Sorry - I've done my best by diagram and text. Hopefully it will be clearer to others.


Yellow Saddle said:


> That's [there needs to be a 'surplus' vertical force component to resist the fork pushing down?] where I think you go wrong. Please try and show that in a force diagram. I can't get my head around your ASCII diagram.


I have revised the 'ASCII' diagram which might now make more sense to you - it seeks first to look at the forces on the fork dropout and then the forces on the hub, and illustrate that the upper spokes 'pull' upwards more than the the lower spokes 'pull' downwards, and that the magnitude of the difference is equal to the weight borne by the wheel.


Yellow Saddle said:


> I'm going to resist the distraction about metal fatigue.


I thought that might pique your interest, though clearly, as a distraction technique, it failed.


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## Salar (11 Jan 2019)

Ajax Bay said:


> and illustrate that the upper spokes 'pull' upwards more than the the lower spokes 'pull' downwards, and that the magnitude of the difference is equal to the weight borne by the wheel.



Don't you mean the upper spokes take more tension and the lower spokes take less tension?


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## Ajax Bay (11 Jan 2019)

united4ever said:


> Anything I should be looking for before just replacing another spoke? is it easy to do for a fairly hands off cyclist who usually uses lbs for much more than puncture or minor tweaks? Should I look at new wheel?





Pale Rider said:


> Apart from comedy physics, has anyone answered the OP?
> It's worth replacing a single broken spoke, but if you get a series it's full wheel rebuild time with all new spokes.
> That may - or may not - be cheaper/dearer than a new factory built wheel.


I think the OP's questions were answered on Page 1 - perhaps worth scanning (regret I cannot see your contribution). Your summary is fair but some TMN awards maybe in order -is @Tinyminewt around?
https://www.cyclechat.net/threads/you-know-youre-not-in-london-when.223290/post-4942781
Except this question "is it easy to do for a fairly hands off cyclist who usually uses lbs for much more than puncture or minor tweaks?" My answer: Within expressed OP's skill/inclination parameters - 'No'. First one needs to learn to true a wheel with a spoke key. Then move on to replacing a spoke, and bear in mind that right hand spoke on the rear will require temporary cassette removal and getting the right length spoke.


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## Ajax Bay (11 Jan 2019)

Salar said:


> Don't you mean the upper spokes take more tension and the lower spokes take less tension?


No I didn't mean or (I think) said the first bit, but 'yes' to the latter part.
So  I said: "the upper spokes 'pull' upwards more than the the lower spokes 'pull' downwards" (on the hub).
As the spokes in a loaded wheel move up to the top they revert to their normal static unloaded tension. When spokes are horizontal they are in slightly greater tension than at the top (to stop the wheel's rim going oval from the force exerted on it by the ground). As the spoke goes lower the tension reduces (see my suggestions attempting to quantify that in the adopted model above). The delta (resolved vertical force) between the upper and lower spokes is equal to the wheel's load.


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## Salty seadog (11 Jan 2019)

Much as I am fascinated by these sort of discussions and can get my head around the arguments on either side my only contribution would be....

X+Y=Z.

I'm glad we have some great engineering minds on here, I've learned a lot over the years and am eternally grateful.

anyway, X+Y=Z, lest we forget.


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## Yellow Saddle (11 Jan 2019)

Ajax Bay said:


> No I didn't mean or (I think) said the first bit, but 'yes' to the latter part.
> When spokes are horizontal they are in slightly greater tension than at the top (to stop the wheel's rim going oval from the force exerted on it by the ground).


I have a problem with the use of "oval". That implies that the top part of the rim receives a downward force as if someone is sitting on the wheel. That's not the case. The change of shape is there for reasons I've described above, but the topmost point of the wheel remains exactly the same distance from the hub when the wheel is loaded. 
Most people's assumption that the hub hangs from the spokes implies that the topmost point of the wheel remains static in space.


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## Yellow Saddle (11 Jan 2019)

Ajax Bay said:


> Sorry - I've done my best by diagram and text. Hopefully it will be clearer to others.
> 
> .



Your diagram shows exactly my model, yet you still bring in this concept of surplus vertical forces. There are none. The road pushes up at 500N and the fork/hub pushes down at 500N. To bring in surplus vertical forces the system is out of balance. It is a pity that you can't indicate them on your force diagram.


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## Ajax Bay (11 Jan 2019)

Yellow Saddle said:


> I have a problem with the use of "oval". That implies that the top part of the rim receives a downward force as if someone is sitting on the wheel. That's not the case. The change of shape is there for reasons I've described above, but the topmost point of the wheel remains exactly the same distance from the hub when the wheel is loaded.
> Most people's assumption that the hub hangs from the spokes implies that the topmost point of the wheel remains static in space.


OK, perhaps I should not have used 'oval' but "sometimes I have to simplify in order to keep my audience, and there's no slight intended to my audience."
There is no additional downwards force on the upper section of a loaded wheel's rim (additional, that is, to the forceful but not increased tension of the upper spokes pulling downwards on the rim). The "topmost point of the wheel [rim] remains" the same distance from the hub as the rim is in an unloaded wheel. I've already said that (imo) the use of 'hang' and 'stand' doesn't help one understand the dynamics.


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## Ajax Bay (11 Jan 2019)

Yellow Saddle said:


> Your diagram shows exactly my model, yet you still bring in this concept of surplus vertical forces. There are none. The road pushes up at 500N and the fork/hub pushes down at 500N. To bring in surplus vertical forces the system is out of balance. It is a pity that you can't indicate them on your force diagram.


If one considers the system as a whole, there are no unbalanced forces (static wheel - Newton init).
But considering just the wheel, its load bearing function is to accept the normal force from the ground and transmit it via spokes and rim through the hub to the fork (which is applying the downwards load on the wheel). Forces acting on the hub from within the wheel have to result in that vertical upwards force - and that resultant upwards force is the difference in tension, resolved vertically, between the upper spokes (normal tension) and the lower spokes (reduced tension). 
There - that's 3+ lines without using the 's' word.
Load = Upper spoke tensions (resolved and summed) minus lower spoke tensions (resolved and summed).


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## Yellow Saddle (11 Jan 2019)

Ajax Bay said:


> OK, perhaps I should not have used 'oval' but "sometimes I have to simplify in order to keep my audience, and there's no slight intended to my audience."
> There is no additional downwards force on the upper section of a loaded wheel's rim (additional, that is, to the forceful but not increased tension of the upper spokes pulling downwards on the rim). The "topmost point of the wheel [rim] remains" the same distance from the hub as the rim is in an unloaded wheel. I've already said that (imo) the use of 'hang' and 'stand' doesn't help one understand the dynamics.





Ajax Bay said:


> If one considers the system as a whole, there are no unbalanced forces (static wheel - Newton init).
> But considering just the wheel, its load bearing function is to accept the normal force from the ground and transmit it via spokes and rim through the hub to the fork (which is applying the downwards load on the wheel). Forces acting on the hub from within the wheel have to result in that vertical upwards force - and that resultant upwards force is the difference in tension, resolved vertically, between the upper spokes (normal tension) and the lower spokes (reduced tension).
> There - that's 3+ lines without using the 's' word.
> Load = Upper spoke tensions (resolved and summed) minus lower spoke tensions (resolved and summed).



OK, I get it. Your end result is exactly the same as mine, via exactly the same mechanism, but you don't like to use the term "standing". 

That's your choice but your diversion is a helluva mouthful.


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## Milkfloat (11 Jan 2019)

In my over simplistic mind - I see a way to visualise that a wheel does not hang is turn a wheel on its side and squeeze the wheel at the rim and the hub, the spoke tension may reduce slightly but nothing is hanging. That is probably nonsense, but it keeps me happy.


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## Yellow Saddle (11 Jan 2019)

Milkfloat said:


> In my over simplistic mind - I see a way to visualise that a wheel does not hang is turn a wheel on its side and squeeze the wheel at the rim and the hub, the spoke tension may reduce slightly but nothing is hanging. That is probably nonsense, but it keeps me happy.


No, that's not nonsense. That's exactly the type of thinking required to figure out what's happening. Even, get up on a ladder and squeeze the wheel against the ceiling (holding onto the axle of course).


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## Milkfloat (11 Jan 2019)

Yellow Saddle said:


> No, that's not nonsense. That's exactly the type of thinking required to figure out what's happening. Even, get up on a ladder and squeeze the wheel against the ceiling (holding onto the axle of course).



I guess even a stopped clock is right twice a day. The ceiling explanation is far better than mine, although I don't need a ladder and therefore a helmet


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## Ajax Bay (11 Jan 2019)

Yellow Saddle said:


> you don't like to use the term "standing".


S is for 'surplus'!


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## Yellow Saddle (11 Jan 2019)

Ajax Bay said:


> S is for 'surplus'!


Surplus is for budgets, in which case there is none.


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## overmind (11 Jan 2019)

Milkfloat said:


> I guess even a stopped clock is right twice a day. The ceiling explanation is far better than mine, although I don't need a ladder and therefore a helmet



Agreed the ceiling analogy helped me understand also.


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## roubaixtuesday (11 Jan 2019)

I was contemplating this on my cycle home, and have a thought experiment to offer which may clarify things. 

Or may not, naturally!

The rim is considered infinitely stiff in the following. 

Three steps:

1. Consider a wheel with a single spoke. The spoke must be vertically upwards from the hub. A weight, W is applied at the hub. The tension in the spoke is W; the infinitely stiff rim transmits the force to the ground where there is a reaction force W. All the weight is supported in extra tension in the spoke. 

2. Now, consider a wheel with two spokes. These spokes are infinitely stiff, so do not elongate under load. They have a pre load tension, P, which obviously must be equal in both spokes. The spokes are vertical, and the load W is applied at the hub. We simply add the solution to (1): the upper spoke has tension (P+W) and the lower spoke has tension P. 

This brings our first conclusion: In the absence of elasticity, all the weight is supported by increased tension in the upper spokes. 

3. We now allow the spokes to be elastic. Both spokes must deform by the same amount as they form a straight line, and the rim is infinitely stiff. The tension in the lower spoke must reduce, as its length reduces. We will call this elasticity reduction E. The tension in the upper spoke must also reduce by the same amount, to keep the overall hub forces in balance. 

The upper spoke now has a tension of (P+W-E)

The lower spoke has a tension of (P-E)

This leads to our second conclusion: allowing for elasticity, tension in upper spokes will increase, _and_ tension in lower spokes will decrease. The amount of each depends on the elasticity of the spokes. 

I hypothesize that these, whilst proved only for a two spoke stiff rimmed wheel, hold generally for a wheel with many spokes and an elastic rim. I don't propose to do the maths to prove it!

Criticism of above most welcome.


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## Ming the Merciless (11 Jan 2019)

Well a single spoke pointing downwards has nothing but air underneath it and in the absence of spoke pointing upwards to counteract the forces, there is nothing to stop that spoke moving downwards towards the road. Remember the spoke is not supported from below by the rim, it does not sit on the rim, it just passes through a hole and will quite happily fall out on its own. It is only constricted from moving towards the hub by the nipple, there is no such constraint or constriction moving the other way


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## roubaixtuesday (11 Jan 2019)

YukonBoy said:


> Well a single spoke pointing downwards has nothing but air underneath it and in the absence of spoke pointing upwards to counteract the forces, there is nothing to stop that spoke moving downwards towards the road. Remember the spoke is not supported from below by the rim, it does not sit on the rim, it just passes through a hole and will quite happily fall out on its own. It is only constricted from moving towards the hub by the nipple, there is no such constraint or constriction moving the other way



In the thought experiment, the wheel is static. For the first part, with a single spoke, it points upward. When a second spoke is added, that one points downward. 

This is the simplest way I can think you allow the problem to be broken down into its key elements.


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## Ming the Merciless (11 Jan 2019)

roubaixtuesday said:


> In the thought experiment, the wheel is static. For the first part, with a single spoke, it points upward. When a second spoke is added, that one points downward.
> 
> This is the simplest way I can think you allow the problem to be broken down into its key elements.



Ah ok so the single spoke pointed upward supports the hub (below) on its own, then you add a downward pointing spoke. Bit like what you will see in the real world if you build a wheel.


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## roubaixtuesday (11 Jan 2019)

YukonBoy said:


> Ah ok so the single spoke pointed upward supports the hub (below) on its own, then you add a downward pointing spoke. Bit like what you will see in the real world if you build a wheel.



Yup.


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## Ming the Merciless (11 Jan 2019)

roubaixtuesday said:


> Yup.



Chandelier is a good way of thinking of it.


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## PapaZita (11 Jan 2019)

roubaixtuesday said:


> I was contemplating this on my cycle home, and have a thought experiment to offer which may clarify things.



I was thinking along similar lines, but came to a slightly different conclusion! In your step 2, why is the load not shared equally between the two spokes? (P+W/2) and (P-W/2)?

I skipped the idea of infinitely stiff spokes, and just considered elastic ones. The change in length of a spoke is proportional to the change in load. The rim stays round (because it's still infinitely stiff), so as the hub moves in the direction of the load, one spoke grows in length by exactly the same amount as the other contracts. The change in tension in each spoke must be equal and opposite.

This suggests to me that, with an infinitely stiff rim, the load would be borne equally by the upper and lower spokes. Yet, we do know (e.g. from measurement) that it really is the lower spokes that do most of the work in real wheels. Can we conclude that the difference is due to the fact that rims are actually not very stiff?

Intuitively, I think it makes sense that deformation of the elastic rim (radially) occurs mostly in the region where it contacts the road. The lower spokes must be the ones getting shorter, and therefore, must be the ones doing the work. You wouldn't expect a 'flat spot' on top of the wheel.


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## roubaixtuesday (11 Jan 2019)

_why is the load not shared equally between the two spokes? (P+W/2) and (P-W/2)?_

Statics is linear, so you can add any two valid solutions.


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## roubaixtuesday (11 Jan 2019)

PapaZita said:


> I was thinking along similar lines, but came to a slightly different conclusion! In your step 2, why is the load not shared equally between the two spokes? (P+W/2) and (P-W/2)?
> 
> I skipped the idea of infinitely stiff spokes, and just considered elastic ones. The change in length of a spoke is proportional to the change in load. The rim stays round (because it's still infinitely stiff), so as the hub moves in the direction of the load, one spoke grows in length by exactly the same amount as the other contracts. The change in tension in each spoke must be equal and opposite.
> 
> ...



Having thought some more, I think you're right. In my version, E ends up as W/2.


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## PapaZita (11 Jan 2019)

roubaixtuesday said:


> Statics is linear, so you can add any two valid solutions.



So, let’s change step 1 to a lower spoke bearing the force W in compression. Now, in step 2, we get an upper spoke with tension P, and a lower spoke with tension P-W. (Of course, real wire spokes don’t do compression, but I think it’s fine for the purposes of this analysis, particularly when W < P). 

What does this mean? Is your method invalid? It’s been a long time since I studied it. I know it’s OK to superpose different load cases on the same structure. Are we allowed to change the structure rather than the load? Are there two (or more) equally valid solutions?


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## silva (12 Jan 2019)

I think a spoke has everything to do with tension not pressure. 
Could the simplest viewpoint then not be alike a spoke is a rope that is knotted to a ring and in a center of that ring to others?


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## SkipdiverJohn (12 Jan 2019)

PapaZita said:


> This suggests to me that, with an infinitely stiff rim, the load would be borne equally by the upper and lower spokes. Yet, we do know (e.g. from measurement) that it really is the lower spokes that do most of the work in real wheels. Can we conclude that the difference is due to the fact that rims are actually not very stiff?.



When a bike is just coasting; i.e. the wheels are rotating and in a straight line but not being either driven by the rider pedalling or being slowed down by the application of the brakes, I cannot see how any spokes other than the top ones are actually doing any work. Spokes cannot be compressed, because if you push the edge of the rim towards the hub, all that happens is the tension comes off the spoke and the nipple becomes loose! A loose spoke rattling around in its hole cannot be carrying any load! When a bike is being accelerated or braked though, there are forces involved that are trying to twist the wheel rim relative to the hub, and if cornering forces are present, then those will be trying to push the hub out of the wheel sideways along the axis of the wheel axle.


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## Ajax Bay (12 Jan 2019)

Morning - sunny to start with early doors down here. Lovely.


roubaixtuesday said:


> 3. We now allow the spokes to be elastic. Both spokes must deform by the same amount as they form a straight line, and the rim is infinitely stiff. The tension in the lower spoke must reduce, as its length reduces. We will call this elasticity reduction E. The tension in the upper spoke must also reduce by the same amount, to keep the overall hub forces in balance.
> The upper spoke now has a tension of (P+W-E)
> The lower spoke has a tension of (P-E)
> This leads to our second conclusion: allowing for elasticity, tension in upper spokes will increase, _and_ tension in lower spokes will decrease. The amount of each depends on the elasticity of the spokes.


Able to stay with you till the last point. Your conclusion seems plausible until E=W when its first element fails: tensions in the upper spokes do not increase. For me E=W so upper spoke tension (in the two-spoke wheel) stays at P and lower spoke tension drops to P-W (and I now see that @PapaZita sort of suggested this yesterday). And this does not depend on how elastic the spokes are, provided they are elastic (your model in scenario 3), so I think that "The amount of each [tension increase/decrease] depends on the elasticity of the spokes." is false.
You may wish to consider a scenario where the top spoke is thinner (and more elastic) and the bottom spoke is thicker (and less elastic). Can the (unloaded) tensions be the same if the hub is to stay central? Notwithstanding that, how do the tensions (two spoke wheel, stiffer than a stiff one rim) vary when a load is applies to the hub (balanced by an opposite normal reaction force at the (bottom of the) rim.


SkipdiverJohn said:


> I cannot see how any spokes other than the top ones are actually doing any work.


Depends what you mean by 'work'. When static, don't think any spokes do any 'work' (in the physics sense of 'work'). Work = force through a distance so the work done by a rotating spoke is an integral over a cycle of its elongation (for a 45kg load this is about 0.01mm) times the (?average?) tension. All the 'work' is elastic (but not perfectly elastic) so much of the energy consumed is elastically returned but some energy is lost (fast rolling wheels etc etc).
Take a static wheel with no load on it (any orientation). All the tensions will be (more or less, depends on rim) the same. Now place the wheel normally on the ground and apply a load, balanced by the normal force from the ground (wheel still static). The top spoke tensions scarcely change; the bottom spoke tensions drop by (in sum) the force of the load applied; the side spokes' tensions increase slightly to maintain the essentially circular integrity of the rim. So if you mean by "doing any work" applying force to the hub then the upper spokes apply more force than the lower spokes but actually the side spokes apply even more, balanced of course by the opposite spoke.


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## PapaZita (12 Jan 2019)

SkipdiverJohn said:


> I cannot see how any spokes other than the top ones are actually doing any work. Spokes cannot be compressed, because if you push the edge of the rim towards the hub, all that happens is the tension comes off the spoke and the nipple becomes loose! A loose spoke rattling around in its hole cannot be carrying any load!



It’s certainly true that spokes can’t be compressed, and if a spoke ever becomes so loose that it’s rattling around then it can’t contribute to the structure of the wheel.

But, remember that spokes start with an awful lot of tension, even before you put any load on the wheel. Something like the equivalent of a 100 kg weight pulling on each one. This is why they ping if you pluck them. And, compression is just negative tension, and as @roubaixtuesday said above, the system is linear, so we can just add up the different loads. 

So, suppose you put a load on the wheel, e.g. by sitting on the bike, that could only be supported by compressing a bottom spoke. Say that load was the equivalent of 25 kg of weight compressing the spoke. But the spoke started with 100 kg of tension. If we add up the loads we have the original 100, minus the 25 applied load (because adding compression is the same as subtracting tension). The spoke now has a tension equivalent to a 75 kg weight hanging off it. It’s still in tension, just less than before. 

If the load applied is so great that it’s bigger than the initial tension in the spoke, either because the load is huge, or the spoke wasn’t very tight to begin with, that’s when the spoke goes slack and wobbles around in its hole. That’s a situation that we want to avoid. 

The initial tension in the wheel is what allows spokes to appear to be working ‘in compression’. Of course, some spokes may support loads by increasing in tension too. The question is, which mechanism is more prevalent, and which spokes are doing it?

I wonder if an analogy helps? Suppose we’re having a tug of war competition, both leaning back, in equilibrium, with lots of tension in the rope. We all know that you can’t push on a rope, but I can make you fall over backwards, just by momentarily reducing the amount I’m pulling.


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## Ajax Bay (12 Jan 2019)

From a John Forrester article (adapted):
It explains how the spokes carry the cyclist's weight. When we build a wheel, all the spokes are stretched in tension as we tighten them, until (with a true rim in a well-built wheel) all the spokes are pulling almost evenly. Now if we load the wheel by applying weight through the hub axle (the normal way) the bottom part of the rim where the tire touches the ground gets forced inward. This inward movement shortens the distance between hub and rim and thereby reduces the tension force in the bottom few spokes. These bottom few spokes then pull the hub downward less strongly than they did before the load was applied; the reduction in downward force is just equal to the weight applied to the hub, so the hub (and all the wheel except the bottom two inches or so of the rim) drops the few thousandths of an inch by which the rim is deflected, and then remains at that level. (Of course the tire deflects also; its effect is a change in level many times that of the wheel deflection.)
When you are on your bicycle your weight is supported by the pull of the spokes on the hubs; it's just that the downward pull (by the lower spokes) is less than it would have been had you not been on the bike.


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## roubaixtuesday (12 Jan 2019)

Ajax Bay said:


> Morning - sunny to start with early doors down here. Lovely.
> 
> Able to stay with you till the last point. Your conclusion seems plausible until E=W when its first element fails: tensions in the upper spokes do not increase. For me E=W so upper spoke tension (in the two-spoke wheel) stays at P and lower spoke tension drops to P-W (and I now see that @PapaZita sort of suggested this yesterday). And this does not depend on how elastic the spokes are, provided they are elastic (your model in scenario 3), so I think that "The amount of each [tension increase/decrease] depends on the elasticity of the spokes." is false.
> You may wish to consider a scenario where the top spoke is thinner (and more elastic) and the bottom spoke is thicker (and less elastic). Can the (unloaded) tensions be the same if the hub is to stay central? Notwithstanding that, how do the tensions (two spoke wheel, stiffer than a stiff one rim) vary when a load is applies to the hub (balanced by an opposite normal reaction force at the (bottom of the) rim.
> ...



"For me E=W"

Why?


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## roubaixtuesday (12 Jan 2019)

Expanding on the last, it is clearly possible from a statics perspective for the change in tension to be entirely in the upper spokes.

It's only deformation in the system which defines where the load is taken. 

Thinking about the two spoke system, for simplicity, if all the change in tension were in the lower spoke, it would reduce in length. The upper spoke would then increase in length _and would therefore increase in tension as a result. 
_
So I think it's not possible to have the entire change in load either on the upper, or on the lower spokes. It must be shared.


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## roubaixtuesday (12 Jan 2019)

There was talk somewhere above of a reference where these tensions were measured. Can anyone post a link please?


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## Yellow Saddle (12 Jan 2019)

roubaixtuesday said:


> There was talk somewhere above of a reference where these tensions were measured. Can anyone post a link please?



You guys haven't bothered to read the thread properly and are now trying to re-hash the debate from the ground up.

There was no mention of tension measured, just an experiment to show a variance in tension or not. It is in the thread. Read it.


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## PapaZita (12 Jan 2019)

Ajax Bay said:


> From a John Forrester article (adapted): #snip



I like this way of looking at it. The deflection of the rim is directly related to the change in tension of the spokes, and it makes intuitive sense, to me, that the deflection is going to occur at the bottom, near to where the force from the road is applied.

What I’m still missing is how to show, with engineering and maths, that this is what _will _happen. I’ve a feeling I once knew how to approach such an analysis, but I fear it’s beyond me now.


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## Mr Celine (12 Jan 2019)

SkipdiverJohn said:


> Spokes cannot be compressed, because if you push the edge of the rim towards the hub, all that happens is the tension comes off the spoke and the nipple becomes loose! A loose spoke rattling around in its hole cannot be carrying any load!



So, go and build a radially spoked wheel on a very stiff rim but only screw the nipples in far enough to just contact the rim, so that there is no tension at all on any spokes. If you put that wheel on a bike then you are correct in so far as the bottom spokes cannot take any load and the hub must be hanging from the top spokes, which are able to take a load in tension. 

But that is not how a spoked wheel works in practice and you wouldn't want to ride a bike with such a wheel. All the spokes in a properly built wheel are under a tensile force which greatly exceeds any compressive force that they undergo. The spokes at the bottom of the wheel are carrying a compressive load but are still under tension. 

For an example of the opposite scenario consider a simply supported pre-stressed concrete beam. The entire beam is always in compression, but the lower half is carrying a tensile load.


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## PapaZita (12 Jan 2019)

roubaixtuesday said:


> There was talk somewhere above of a reference where these tensions were measured. Can anyone post a link please?



I have done that, for my own amusement, in the past. I’m sorry, I’ve nothing to link to. I may attempt to recreate it, if I get time and a willing helper/weight. 

Jobst Brandt’s book does have a section on the loads on a wheel, with diagrams of the deformation of a wheel produced by finite element analysis. He does radial, braking, and driving loads, in isolation and in combination. Here’s a sneaky preview of the radial load case, which is mostly what we’re discussing:


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## Salar (12 Jan 2019)

Well,

I've just quickly ran a basic"wheel" through one of my analysis programmes. Ignore units, measurements etc, this is just to show the principle.

The bottom three spokes are considered as being "supported" at the ground.

The green lines indicate the change of forces in the members.

The green line to the rim is the radial axial load.

The green lines in the bottom three spokes indicate reduced tension in these spokes only, no other spokes.

This computer analysis tallies with @Yellow Saddle sketch.


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## Yellow Saddle (12 Jan 2019)

Salar said:


> View attachment 446743
> Well,
> 
> I've just quickly ran a basic"wheel" through one of my analysis programmes. Ignore units, measurements etc, this is just to show the principle.
> ...



Please say it.


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## flake99please (12 Jan 2019)

I had 4 go on my front wheel last night. Only ever had 1 go in a lifetimes worth of riding before that. I’m working on assumption that it may be something to do with the fact that I had put my bike (front wheel) in front of the hall radiator yesterday evening. They all went within a space of one minute at various locations on the wheel.


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## Salar (12 Jan 2019)

Yellow Saddle said:


> Please say it.



 I'll let other say you are correct. Seriously you are right. I could put a lot more properties etc in but the principle remains the same.


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## Yellow Saddle (12 Jan 2019)

flake99please said:


> I had 4 go on my front wheel last night. Only ever had 1 go in a lifetimes worth of riding before that. I’m working on assumption that it may be something to do with the fact that I had put my bike (front wheel) in front of the hall radiator yesterday evening. They all went within a space of one minute at various locations on the wheel.



Something is the operative word, but not because.

As stated before, spokes break in fatigue and fatigue breaks develop over time. The last straw breaks the camel's back and the rim heating up and expanding to put more tension on the spokes, probably did the job. However, had the heating not done it, the next ride would have. Except that the next ride would only have broken one spoke because you would have stopped when it broke.

Have a look at the broken ends. They will be absolutely perpendicular to the spoke. There will be a large grey area indicating that the break has taken place over time and then a small shiny bit with a little pip. That's the straw that broke the camel's back and the only bit that broke in tension.


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## Yellow Saddle (12 Jan 2019)

Salar said:


> I'll let other say you are correct. Seriously you are right. I could put a lot more properties etc in but the principle remains the same.


No not that. I don't care who's right, I just care about following a sensible procedure in the debate.

Say it.


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## roubaixtuesday (12 Jan 2019)

So, on the shoulders of giants and all, here's what looks like a definitive study, including experimental measurement of tensions.

Fig 6 is the money shot.

It turns out that the lower spokes close to contact with the ground do indeed, as suggested here, take most of the change in tension, as a reduction.

*All* the other spokes, top middle and even in the lower half further from the ground show an almost uniform but small increase in tension.

http://www-civ.eng.cam.ac.uk/cjb/papers/p20.pdf


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## PapaZita (12 Jan 2019)

roubaixtuesday said:


> So, on the shoulders of giants and all, here's what looks like a definitive study, including experimental measurement of tensions.



From the very engineering department where I mostly snoozed through structures lectures!  Thank you, I will enjoy reading that.


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## andrew_s (12 Jan 2019)

What strikes me about all these "hang or stand" threads is that generally everyone seems to agree about the detail of what's actually happening (see Yellowsaddle's or Ajax Bay's drawings back on page 3, or roubaixtuesday's post above), and that the argument is about how to describe what's happening in words.


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## Ajax Bay (12 Jan 2019)

From a Park Tools article.
*Effect of Radial Load*
Rims get a downward load at the hub just by sitting on the bike and riding. This stress tends to flatten the rim slightly at the bottom, close to the 6:00 position. Because of this flattening, the bottom few spokes will drop slightly in tension. However, at the same time, the spokes to the left and right side of the bottom, at the 3:00 and 9:00 positions, rise slightly in tension. The spokes at the 12:00 position do not gain tension . . . every time the wheel rotates, each spoke goes through this cycle of getting looser and tighter.


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## Yellow Saddle (12 Jan 2019)

andrew_s said:


> What strikes me about all these "hang or stand" threads is that generally everyone seems to agree about the detail of what's actually happening (see Yellowsaddle's or Ajax Bay's drawings back on page 3, or roubaixtuesday's post above), and that the argument is about how to describe what's happening in words.



Not really, there wasn't any consent here, if any, until just a few months ago. It wasn't just the nomenclature, it was the concept. 

This week saw a milestone on this forum. It's been four years on this forum of arguing the case before one person saw the light, maybe a year ago, I'm not exactly sure. In the last week, a flood of others finally grasped as well. In those four years the naysayers were loud, overwhelming and acting like a mob. In those four years I've repeatedly suggested a simple experiment to empirically prove the point and help with the understanding, but not a single person took me up on it, relying instead on intuition and common sense, both of where were out of kilter. The experiment is extremely simple and requires no equipment other than a bike and a buddy. In those four years we've had several engineers promising me that they would produce a force diagram showing their version of a model, but none came to the party, usually buggering off on a huff because of the way I sometimes say things, using that as an excuse to not face their limitations.

I can't list the number of fallacies committed in the process on my hands and toes. I don't have enough digits. The fallacies range from ad-hominem (the most common), to appeal to authority, straw man arguments, argument from popularity, faulty comparison, you name it, it was committed. It got real nasty at times. At least one reasonable man left the forum because of that.

What absolutely surprised me is that the suggestion of pressing the wheel against a wall (one I tried several times before) and the new one of pressing the wheel against the ceiling, helped one or two people grasped the concept. That I'm very happy about and I'll use that in future and certainly when I get an opportunity again one day to teach it to structural engineering students. 

I still maintain that the correct terminology is to say the load stands on the bottom spokes. The fact that the mechanism is reversed doesn't matter, it is just a brain-switch you need to make. Looking at the tension graphs show it empirically. 

This tread should become a sticky.


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## Ming the Merciless (12 Jan 2019)

Salar said:


> View attachment 446743
> 
> Well,
> 
> ...



What are the bottom three spokes supported by, as it certainly is not the rim?


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## Yellow Saddle (12 Jan 2019)

YukonBoy said:


> What are the bottom three spokes supported by, as it certainly is not the rim?



They are in tension between the rim and the hub just like all the other spokes and nothing supports them or needs to "support" them.


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## Ming the Merciless (12 Jan 2019)

Yellow Saddle said:


> They are in tension between the rim and the hub just like all the other spokes and nothing supports them or needs to "support" them.



So his assumption in his modeling was wrong and he needs to go back and redo it. The conclusion will be the same but not for the reason he thinks.


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## Yellow Saddle (12 Jan 2019)

YukonBoy said:


> So his assumption in his modeling was wrong and he needs to go back and redo it. The conclusion will be the same but not for the reason he thinks.



Who is he and what was his assumption?


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## Ming the Merciless (12 Jan 2019)

Yellow Saddle said:


> Who is he and what was his assumption?



Well look at my post you replied to, I quoted the persons post it is all there and he assumes the bottom three spokes are supported differently to all the others.


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## Yellow Saddle (12 Jan 2019)

YukonBoy said:


> Well look at my post you replied to, I quoted the persons post it is all there and he assumes the bottom three spokes are supported differently to all the others.


Sorry, at first the diagram in question post didn't show so I assumed you referred to the author of the paper and the last drawing in the thread.

From what I can see, he (@Salar) made no assumptions which were either proven right or wrong. I think the "support means contact or at the very least, within the LAZ. I'll let him comment on his own drawing.

But, I'll stick with the answer that the bottom spokes don't need support to stay upright or straight since they are in tension.


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## Ming the Merciless (12 Jan 2019)

Yellow Saddle said:


> Sorry, at first the diagram in question post didn't show so I assumed you referred to the author of the paper and the last drawing in the thread.
> 
> From what I can see, he (@Salar) made no assumptions which were either proven right or wrong. I think the "support means contact or at the very least, within the LAZ. I'll let him comment on his own drawing.
> 
> But, I'll stick with the answer that the bottom spokes don't need support to stay upright or straight since they are in tension.



We are agreed but his support comment about the bottom three spokes seems a strange comment to make. All the spokes are held in tension the same way. We both agree there is no support and it should not be necessary for him to make that incorrect assumption in his modeling.


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## Ajax Bay (12 Jan 2019)

PapaZita said:


> From the very engineering department where I mostly snoozed through structures lectures!


"The tests were carried out while the writers were employed at Imperial College (assume London)" ( last paragraph). Stepping on and off the Engineering Department's _pater-noster_ lift was the highlight of my attendance at structures lectures bitd.


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## Ajax Bay (12 Jan 2019)

Yellow Saddle said:


> I still maintain that the correct terminology is to say the load stands on the bottom spokes. The fact that the mechanism is reversed doesn't matter,


I know you won't mind if I say that I differ. I maintain that saying that the load "stands on the bottom spokes" is misuse of the word 'stands', is therefore not correct terminology. Saying that the load 'hangs' on the upper spokes is false too - ie a misuse of the word 'hangs' and use of either terminology does not help to understand how a wheel supports a load.
Not sure what you mean by "the mechanism is reversed" but I suspect that I'd argue that the 'reversal' absolutely does matter to those trying to understand how a wheel supports a load.


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## andrew_s (12 Jan 2019)

Yellow Saddle said:


> Not really, there wasn't any consent here, if any, until just a few months ago. It wasn't just the nomenclature, it was the concept.


What I meant was that it seems to be readily accepted that, in an actual wheel that you could use on a bike...
a) all the spokes are at a fairly high tension.
b) when the wheel is loaded the tension in the bottom 2 or 3 spokes is reduced.
c) the tension in all the other spokes is more or less unchanged.

It's in translating that information into an explanation of what keeps the hub off the ground that everything falls apart and the hang or stand arguments arise.


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## Ajax Bay (12 Jan 2019)

roubaixtuesday said:


> [Ajax Bay]: "For me E=W"
> Why?
> It is clearly possible from a statics perspective for the change in tension to be entirely in the upper spokes.
> It's only deformation in the system which defines where the load is taken.
> ...


Replying to the posts you made yesterday evening.
"clearly possible from a statics perspective" Perspective which offers no utility, I suggest.
"It's only deformation in the system which defines where the load is taken." In an elastic system, external forces will result in deformation (and movement if unbalanced).

We are considering scenario 3, where the two spokes (one up, one down) are elastic.
Pasting a link to your post for ease of reference: https://www.cyclechat.net/threads/why-do-my-spokes-keep-breaking.244392/post-5498719
Try this. Convert the 'simple' two spoke system to one pre-tensioned 'spoke' spanning the diameter of the rim vertically with a neat attachment point at the centre of this diameter spoke. Then apply a vertical (downwards) load to the centre point (same as a load through the drop outs) and an equal and opposite force upwards where the spoke reaches the rim/ground.

The top half of the spoke has *no net increase in tensile force* (the resultant of the load and normal force is nil). The bottom half of the spoke has a compressive force applied. Fortunately this force is much less than the magnitude of the pre-tension in the spoke so it doesn't buckle and fail: it stays in tension but less than its starting tension by 'W'.
That's why E (which you defined as the reduction in tension due to elasticity) = W (the load applied (at the centre (hub)).

"if all the change in tension were in the lower spoke, it would reduce in length" absolutely and this is what happens in the real world. The rim in the contact (with the ground) area and adjacent distorts from a perfect circle (by <20 microns for a 622 wheel and 500N load), the lower spokes contract and the tensions in the lower spokes reduce accordingly. When the wheel is loaded the upper spoke(s) do not measurably increase in length (their tension is essentially unchanged from their pre-load tension).


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## andrew_s (12 Jan 2019)

To get back on topic 

As stated, the OPs spokes keep breaking because they are fatigued, and as many other spokes will have started to crack but not yet actually broken, the only thing to do to avoid having the wheel fixed every few weeks (or even days) is to rebuild the wheel with new spokes.

The root of the problem is that the wheel wasn't stress relieved after being built, as is fairly common in cheaper factory or new bike wheels. 
Stress relieving is done by briefly bringing each spoke up to a much higher tension than the static build tension (up to double). This is usually done by squeezing pairs of spokes together hard, forcing the middles of the spokes sideways. If you are squeezing hard enough, you'll probably want gardening gloves to protect the hands.
https://www.sheldonbrown.com/brandt/stress-relieving.html

It is possible that you could give the wheel a good hard stress relief session, replace the spokes that this broke (no loss, they would have broken soon anyway), then stress relieve the wheel again. However, the chances of getting a bike shop to do this are fairly low.


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## andrew_s (12 Jan 2019)

roubaixtuesday said:


> Thinking about the two spoke system, for simplicity,


The two-spoke system may be simple, but it's not a wheel (you couldn't put it on a bike and ride), so there's no point thinking about it


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## Ajax Bay (12 Jan 2019)

andrew_s said:


> The two-spoke system may be simple, but it's not a wheel (you couldn't put it on a bike and ride), so there's no point thinking about it


The rim is defined as rigid so perhaps you could. Fair bit of tension in the two spokes when they went through horizontal, mind. If the spokes could take compression then perhaps a three or four spoke wheel would roll OK.


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## roubaixtuesday (13 Jan 2019)

andrew_s said:


> The two-spoke system may be simple, but it's not a wheel (you couldn't put it on a bike and ride), so there's no point thinking about it



You've missed the point entirely. 

I offered the two spoke model not as a practical wheel, but as a way to help think conceptually about the problem. 

Far more illustrious thinkers have used similar approaches. 

https://en.wikipedia.org/wiki/Einstein's_thought_experiments


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## Ajax Bay (13 Jan 2019)

andrew_s said:


> the OPs spokes keep breaking because they are fatigued
> . . .
> The root of the problem is that the wheel wasn't stress relieved after being built


Are you suggesting that the spokes of properly (?and regularly) stress relieved wheels do not fatigue and finally part?


andrew_s said:


> you could give the wheel a good hard stress relief session, replace the spokes that this broke (no loss, they would have broken soon anyway),


Have you ever actually managed to break a spoke during "a good hard stress relief session" ()?
I see Jobst Brandt said he'd done this:
"My first experience with this [squeezing spokes to achieve much higher tension levels temporarily] was years ago when I had frequent spoke failures and wanted to be done with it by attempting to break any spoke that was about to break. That is where I stumbled onto stress relieving. I broke two more spokes by forcefully stress relieving the
wheel and then there were none for a long time."


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## Yellow Saddle (13 Jan 2019)

Ajax Bay said:


> Are you suggesting that the spokes of properly (?and regularly) stress relieved wheels do not fatigue and finally part?


There is no point in regularly stress-relieving a spoke. Stress relief is done once, after finishing building the wheel, to normalise internal stress in the spoke which derived from the bending, stamping and threading steps in manufacture. Stress relieving later on in the wheel's life is useless. 



Ajax Bay said:


> Have you ever actually managed to break a spoke during "a good hard stress relief session" ()?
> I see Jobst Brandt said he'd done this:
> "My first experience with this [squeezing spokes to achieve much higher tension levels temporarily] was years ago when I had frequent spoke failures and wanted to be done with it by attempting to break any spoke that was about to break. That is where I stumbled onto stress relieving. I broke two more spokes by forcefully stress relieving the
> wheel and then there were none for a long time."



That incident doesn't indicate regular stress relieving. He just called it stress relieving because he used the same squeezing method to see if he could find spokes which were just about to break. He did. I've done that plenty of times on wheels that came in with spokes broken. I prefer to break one or two more in the workshop than have the customer return a week later with more spokes.

A stress relieved wheel with double-butted spokes (Revos or Competition, it doesn't matter) has a near infinite spoke life, provided the right wheel was designed for the job. By design, I mean that you didn't attempt to fob a 24-spoke wheel off to a 120kg guy, or build tandem wheels with only 36 spokes. My own wheels are built with Revos, 28 spokes on Mavic Open Pro. The wheels have done in excess of 200 000 kms without a single broken spoke, and one one, "tune" to true a slight wobble.

Our little factory built about 30k wheels in 7 years. Each wheel went out with a lifetime (of the wheel) spoke gaurantee. In 14 years (I've beenout of it for 7 years now but someone else is looking after come-backs), we've had less than 6 broken spokes. Four were from sticks, two from fatigue. We had a contract with a reseller of Zipp wheels who brought the wheels into the country as components for tax reasons. We assembled several hundred of those and never had a single spoke break, even though they were ridiculously under-specc'd. However, there were plenty of comebacks on the nipples, which of course being Zipp, were aluminium. I've never had a single brass nipple fail on us. Each time an aluminium nipple breaks on a Zipp wheel, it is high drama. It usually costs more to repair than the original build fee.


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## rogerzilla (13 Jan 2019)

I doubt Brandt broke spokes merely by squeezing pairs of spokes together with his hands, although spokes were not as good back in the day. However, some people also like to torture the spokes by wedging an old crank into the crossings and using it as a lever, and I suppose that could break a spoke if you have no feel for this kind of thing.

For what it's worth, I've only ever had one spoke break, and that was on a very cheap 27" machine-built wheel with "rustless" spokes, that had done quite a lot of winter miles. Decent modern spokes don't break anything like as often as the rubbish ones of the past, even in an indifferently-built wheel; the purpose of good wheelbuilding is more about ensuring the wheel remains true and the nipples never need touching again, not until the rim has worn out.


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## Yellow Saddle (13 Jan 2019)

rogerzilla said:


> I doubt Brandt broke spokes merely by squeezing pairs of spokes together with his hands, although spokes were not as good back in the day. However, some people also like to torture the spokes by wedging an old crank into the crossings and using it as a lever, and I suppose that could break a spoke if you have no feel for this kind of thing.



We used the crank method and I can attest that you cannot break a spoke using that method. Reason is that the crank bottoms out against adjacent spokes and prevents over-extension. However, you can easily pop a rim that way. Some rims are too weak to stress-relieve the spokes. Notably those from Enve. Therefore, Enve wheels break spokes all the time.


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## rogerzilla (13 Jan 2019)

Yes, I use the crank method too and have never had a problem. I also use the squeezing method (with leather gloves) but only at the end of the process.


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## Yellow Saddle (13 Jan 2019)

rogerzilla said:


> Yes, I use the crank method too and have never had a problem. I also use the squeezing method (with leather gloves) but only at the end of the process.


I assume you do the latter in order to correct the spoke arrival angle at the nipple. I've given up on rims that don't allow the nipple to naturally follow the line of the spoke.


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## rogerzilla (13 Jan 2019)

I use Sapim Polyax nipples for large flange hubs and other situations (tiny Brompton wheels) that give a bad spoke/rim angle. Otherwise, yes, the main thing is to get a decent kink where the spoke exits the nipple rather than a soft bend, and it takes quite a bit of force to do this.


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## Salar (14 Jan 2019)

Yellow Saddle said:


> From what I can see, he (@Salar) made no assumptions which were either proven right or wrong. I think the "support means contact or at the very least, within the LAZ. I'll let him comment on his own drawing.



Correct @Yellow Saddle the "supports" are the load affected zone. As you can understand I had to simulate the LAZ and have used engineering terminology.

Without any "support" the wheel would be in free fall. I could have input many "supports" over the LAZ and introduced spring supports etc, but the final result is the same.

Which is, as shown by Yellow Saddles sketch and my quick analysis that only the spokes in the LAZ have their tension reduced. Your mind might tell you otherwise, but my conclusions agree with Yellow Saddle.


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## Ajax Bay (14 Jan 2019)

On a dished rear wheel the LH and RH spokes are at marked different tensions (to the opposite side) (600N and 1000N say). Since the the reduction in tension of the lower spokes (assume LAZ means 'Load Affected Zone'?) is dependent on rim displacement (<20 microns for a 500N load on a 622 wheel) does that mean that the reduction in tension is less in RH spokes than in LH spokes?


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## Ming the Merciless (14 Jan 2019)

Salar said:


> Correct @Yellow Saddle the "supports" are the load affected zone. As you can understand I had to simulate the LAZ and have used engineering terminology.
> 
> Without any "support" the wheel would be in free fall. I could have input many "supports" over the LAZ and introduced spring supports etc, but the final result is the same.
> 
> Which is, as shown by Yellow Saddles sketch and my quick analysis that only the spokes in the LAZ have their tension reduced. Your mind might tell you otherwise, but my conclusions agree with Yellow Saddle.



Can you explain what you mean by support? As you know the spokes in the "load affected zone" are pulling the hub towards the rim just like all the other spokes in the wheel.


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## Yellow Saddle (14 Jan 2019)

Ajax Bay said:


> On a dished rear wheel the LH and RH spokes are at marked different tensions (to the opposite side) (600N and 1000N say). Since the the reduction in tension of the lower spokes (assume LAZ means 'Load Affected Zone'?) is dependent on rim displacement (<20 microns for a 500N load on a 622 wheel) does that mean that the reduction in tension is less in RH spokes than in LH spokes?



No, they all lose equal tension.


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## Ming the Merciless (14 Jan 2019)

Ajax Bay said:


> On a dished rear wheel the LH and RH spokes are at marked different tensions (to the opposite side) (600N and 1000N say). Since the the reduction in tension of the lower spokes (assume LAZ means 'Load Affected Zone'?) is dependent on rim displacement (<20 microns for a 500N load on a 622 wheel) does that mean that the reduction in tension is less in RH spokes than in LH spokes?



See Hooke's law.

*Hooke's law* is a law of physics that states that the force (F) needed to extend or compress a spring by some distance x scales linearly with respect to that distance. (Wikipedia)


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## Pat "5mph" (15 Jan 2019)

*Mod Note:*
We have deleted some of the excellent banter on this thread, sorry about that.
This was to streamline the information for future readers.
This thread will now be pinned on top of the mechanic board.
Thank you to all contributors for taking the time to fully illustrate this interesting topic.


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## Spiderweb (16 Jan 2019)

I've just read the whole thread, my brain is now completely mashed!
I'm going home for a lie down!


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## Ticktockmy (18 Jan 2019)

Same here, my mind is buggered reading this thread, I wonder how people have time to get out on there bikes with the amount of research they do.
Never interests me, if i break a spoke, I just replace it, check the spokes are about the same for tension and the wheel is true. that it. All this forumla stuff is beyound me.


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## Ajax Bay (17 Feb 2019)

rogerzilla said:


> Jobst Brandt also talked about the wheel "standing" on its lowest spokes (equating a reduction in tension with compression). It's annoyed a lot of people over the years. He was correct but his choice of words didn't help much.


I enjoyed a hilly 200 on Thursday and, inter alia, thought about wheels 'standing' on their spokes during the 100,000 odd revolutions.
From Job Brandt's book 'the Bicycle Wheel':
Page 10
"THE WHEEL STANDS ON ITS [BOTTOM] SPOKES
"Of course the wheel is not supported by the bottom spokes only. Without the rest of the spokes, the bottom ones would have no tension. Standing, in this case,means that the spokes at the bottom are the ones that change stress; they are being shortened and respond structurally as rigid columns. They are rigid as long as they remain tensioned."
If the term "standing" is taken to mean 'effecting a change in stress which shortens them (from their static tensioned state)' then fine - odd use of 'standing'.
If Brandt is merely using the 'standing' idea as a medium for helping people realise that wheels don't 'hang' from the top spokes (their tension remains essentially the same as when the wheel is unloaded), that's useful if it achieves the aim without introducing confusion.
I have difficulty with the idea that the tensioned spokes "respond structurally as [if they were] rigid columns" unless what Brandt means is that under decreased stress they shorten as a rigid column would. But that doesn't mean the bottom spokes are 'rigid columns'. And for the idea that a wheel "stands on its bottom spokes" those supports need to be rigid - they aren't: they're thin, flexible wire spokes.
Would one say that tensioned elastic bands "respond structurally as rigid columns" or describe them as "rigid as long as they remain tensioned"?


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## Ajax Bay (1 May 2019)

Henry - 


Henry34 said:


> Uneven tightening might lead to mechanical fatigue causing the spokes to break. There is a sharp rise in the tension on hitting a bump, leading to breaking of the spokes.


Please could you explain why (even significantly) uneven tension might increase the likelihood of a spoke failing through fatigue.
Please could you elaborate on the effect of 'hitting a bump' on the tension of spokes in various positions (ie the ones at the bottom, the ones at the top). Will the ones at the bottom experience a "sharp rise in tension"? Will the ones at the top experience a "sharp rise in tension"? I assume you are suggesting that a "sharp rise in tension" in a spoke will cause it to part. Why? Spokes are pretty strong. Isn't the rim more likely to fail in such circumstance?
Various posts above, which you'll have read, try to articulate the physics to inform your answer.


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## Yellow Saddle (1 May 2019)

Henry34 said:


> Uneven tightening might lead to mechanical fatigue causing the spokes to break. There is a sharp rise in the tension on hitting a bump, leading to breaking of the spokes.



No. Go back and do you homework. There's even a pinned thread that will help you with spokes.


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## durianrider (7 Jun 2019)

Ive found black spokes break easier for some weird reason. Not black mavic spokes but black spokes you might see on an entry level bike. Anyone else had this issue?


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## Yellow Saddle (8 Jun 2019)

durianrider said:


> Ive found black spokes break easier for some weird reason. Not black mavic spokes but black spokes you might see on an entry level bike. Anyone else had this issue?



There are two ways of making stainless steel spokes black: 1) Paint 2) Black Oxide.

Neither method has any effect on the durability of the spoke. A poor quality/badly installed black spoke will break just as quickly as a silver one under the same circumstances.

Paint doesn't last very long on a spoke as it readily chips off. Black oxide on the other hand, is extremely durable. Black spokes cost more than silver spokes.


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## Milkfloat (11 Jul 2019)

Just revisiting this thread about wheels hanging. Even the BBC and their experts get it wrong when trying to teach kids.

https://www.bbc.com/bitesize/articles/zf6v6v4

I will you to debate the gryroscopic effect too.


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## Ming the Merciless (11 Jul 2019)

Milkfloat said:


> Just revisiting this thread about wheels hanging. Even the BBC and their experts get it wrong when trying to teach kids.
> 
> https://www.bbc.com/bitesize/articles/zf6v6v4
> 
> I will you to debate the gryroscopic effect too.



Professional cyclists go ten times faster. Of course they do


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## Yellow Saddle (18 Jul 2019)

Milkfloat said:


> Just revisiting this thread about wheels hanging. Even the BBC and their experts get it wrong when trying to teach kids.
> 
> https://www.bbc.com/bitesize/articles/zf6v6v4
> 
> I will you to debate the gryroscopic effect too.



I just puckered a good dozen washers onto my chair when I read that.

Now imagine the same idiots informing you on climate change, the food pyramid and green cars.


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## si_c (18 Jul 2019)

Yellow Saddle said:


> I just puckered a good dozen washers onto my chair when I read that.
> 
> Now imagine the same idiots informing you on climate change, the food pyramid and green cars.



Food Pyramid. When someone gets buried alive under an EU food mountain innit.


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## Waterwheel (13 Aug 2019)

The most common cause of broken spokes is simply carrying to much luggage on your bike. The second is if the spokes are not properly tensioned. If they are slightly too loose that will put too much strain on a few spokes at a time. If they are too tight they will snap because they are under too much tension. Get you spokes re tensioned at a bicycle shop. Or you may be a very heavy rider in which case you just have to keep on replacing broken spokes until you manage to lose enough weight. I always find that old second hand bikes are most prone to spoke breakage. If that is the case the spokes may be coming to the end of their life and will need replacing.


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## Yellow Saddle (13 Aug 2019)

Waterwheel said:


> The most common cause of broken spokes is simply carrying to much luggage on your bike. The second is if the spokes are not properly tensioned. If they are slightly too loose that will put too much strain on a few spokes at a time. If they are too tight they will snap because they are under too much tension. Get you spokes re tensioned at a bicycle shop. Or you may be a very heavy rider in which case you just have to keep on replacing broken spokes until you manage to lose enough weight. I always find that old second hand bikes are most prone to spoke breakage. If that is the case the spokes may be coming to the end of their life and will need replacing.



Nonsense.


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## Ajax Bay (14 Aug 2019)

Waterwheel said:


> I think that I am one of the oldest people on here as I am nearly 53


First of all:  to CycleChat. As @CarlP has suggested, pretty sure you're below CC median age


Waterwheel said:


> The most common cause of broken spokes is simply carrying to much luggage on your bike. The second is if the spokes are not properly tensioned. If they are slightly too loose that will put too much strain on a few spokes at a time. If they are too tight they will snap because they are under too much tension. Get you spokes re tensioned at a bicycle shop. Or you may be a very heavy rider in which case you just have to keep on replacing broken spokes until you manage to lose enough weight. I always find that old second hand bikes are most prone to spoke breakage. If that is the case the spokes may be coming to the end of their life and will need replacing.


Have you read this thread through?
1. "carrying to (sic) much luggage on your bike." and "Or you may be a very heavy rider in which case you just have to keep on replacing broken spokes until you manage to lose enough weight." Please could explain why a heavy rider or one carrying some luggage will make it more likely a spoke will break? Have you experienced spokes breaking for either of these reasons?
2. "if the spokes are not properly tensioned." Provided the rim is true, what do you mean by 'properly'? How does a rider (say like you) determine whether the spokes on their wheel(s) are 'properly tensioned'?
3. "If they are slightly too loose that will put too much strain on a few spokes at a time." Why will having spokes looser than 'properly tensioned' mean that additional strain (produced by higher tension) goes on a few spokes at a time? In a moving wheel with a load on, the tension increase in spokes, compared to the spokes in a wheel without load is, as a percentage, rather small. All but the bottom few spokes will experience a slight additional tension. The lower spokes will reduce in tension, by a significant amount.
4. "If they are too tight they will snap because they are under too much tension." Why will spokes under 'too' much tension tend to break? Surely the rim will break first.
5. "The spokes may be coming to the end of their life and will need replacing." Quite possibly. But if they are old wheels an an 'old second [or more] hand bike' then probably not worth replacing more than a couple of spokes as once one or two have 'come to the end of their lives' their neighbours will soon be knocking on the mortuary door.


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## itracm (15 Aug 2019)

I have a 27" Dawes which used to regularly snap spokes.
The wheels were laced incorrectly but it didn't stop there.
The recommended tyre pressures were 65 psi.
This is the unbelievable bit: I deflated the tyres to 50 psi and I only lost a couple of spokes in the last two year. Yes, they are cheap spokes.
To prove the point I tried inflating to 65 psi again and lost 2 spokes on my next 3 short rides.
I'm happy to have a slightly softer ride as I don't rush around anymore.
I'm not condoning using anything other than manufacturer's recommendations. However, if worked for me.
Good luck.


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## Ajax Bay (15 Aug 2019)

First of all:  to Cycle Chat.


itracm said:


> However, if [sic] worked for me.


Sorry - what worked for you? What point were you trying to 'prove' by pumping your tyres up a bit? Why do you think there is a any causative effect between spokes parting and tyre pressure 15psi more. For context it would be useful to know tyre width and weight of you plus bike.


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## itracm (16 Aug 2019)

Ajax Bay said:


> First of all:  to Cycle Chat.
> 
> Sorry - what worked for you? What point were you trying to 'prove' by pumping your tyres up a bit? Why do you think there is a any causative effect between spokes parting and tyre pressure 15psi more. For context it would be useful to know tyre width and weight of you plus bike.



Apologies for being so vague. About 2 years ago I was recovering from a back injury and with the aid of a fat bum saddle decided to get back on the bike. Local roads are boneshakers and that's when I let the tyres down a bit. This did assist recovery. After two years I decided to pump the tyres up to their recommended pressure. It was only then, when my spokes started pinging, I remembered the issue. I wasn't trying to prove anything it was a complete coincidence.
I replaced the spokes, inflated to 50 psi and have not lost a spoke since.
I thought it was unbelievable and can't think of any plausible causation.
Just sharing an experience.


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## Yellow Saddle (17 Aug 2019)

This is getting better and better.


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## Pat "5mph" (17 Aug 2019)

Mod Note:
@Yellow Saddle:  (please )
End Mod Note.

@itracm welcome to CC!
I'm no bike mechanic, nor a mechanic at all, but I think your broken spokes were a coincidence, nothing to do with tyre pressure, imo, of course.



Waterwheel said:


> The most common cause of broken spokes is simply carrying to much luggage on your bike.


How much is too much though?
The touring section, then, should be riddled with tales of broken spokes, tourers carrying camping equipment over long distances.
It isn't btw, most tourers mechanicals are snapped cables and punctures.


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## Shadow121 (17 Aug 2019)

Am off to make a spoke propelled rocket, seems like they have mystical
powers that can support serious loads when they are under them.
Wonder if I could just use a few of them and keep them on the bottom
for they seem to be way too weak to hang from.
Next up, turn dropouts upside down as the wheel will have more support.


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## Yellow Saddle (18 Aug 2019)

Pat "5mph" said:


> Mod Note:
> @Yellow Saddle:  (please )
> End Mod Note.


OK, it was a bit naughty. I should have been frank and stated the truth by saying: "This is getting worse and worse."


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## chandsley (24 Aug 2019)

Hey i’ve just bought the trek roscoe 6 19, and i’ve had it for a day been on it maybe 4/5 hours and i do admit i do wheelies and i like swerve stuff and i’ve noticed the wheel is a little buckled not a lot but a little and i don’t know if i’m being para but does wheelie damage the back wheel to a point of not being able to ride it and is it possible to do it so soon?? please i need answers


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## Yellow Saddle (24 Aug 2019)

chandsley said:


> Hey i’ve just bought the trek roscoe 6 19, and i’ve had it for a day been on it maybe 4/5 hours and i do admit i do wheelies and i like swerve stuff and i’ve noticed the wheel is a little buckled not a lot but a little and i don’t know if i’m being para but does wheelie damage the back wheel to a point of not being able to ride it and is it possible to do it so soon?? please i need answers


No and no.


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## chandsley (24 Aug 2019)

Yellow Saddle said:


> No and no.


Cheers mate


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## overmind (30 Sep 2019)

Yellow Saddle said:


> No and no.



Does that mean that the buckle was there to begin with? Otherwise what would have caused the buckle (if it was not doing wheelies)?


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## Ming the Merciless (30 Sep 2019)

overmind said:


> Does that mean that the buckle was there to begin with? Otherwise what would have caused the buckle (if it was not doing wheelies)?



Jumping off kerbs


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## overmind (4 Oct 2019)

I was looking at some wheels in the bike shop yesterday and noticed that the more expensive high-end wheels have much higher spoke tension. What is the reason for this? I've noticed the spokes on my bike (BTwin Triban 3) are tight but not as tight as this.

Would there be any benefit in tightening my spokes? Say, 1/4-1/2 turn all round the wheel and then re-true?


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## si_c (4 Oct 2019)

overmind said:


> I was looking at some wheels in the bike shop yesterday and noticed that the more expensive high-end wheels have much higher spoke tension. What is the reason for this? I've noticed the spokes on my bike (BTwin Triban 3) are tight but not as tight as this.
> 
> Would there be any benefit in tightening my spokes? Say, 1/4-1/2 turn all round the wheel and then re-true?



More expensive wheels often have fewer spokes so require increased tension. If you think about the wheel as a system and the total tension of all the spokes required to keep a wheel circular and true then divide by the number of spokes and you will immediately see the need for greater tension. This is a bit of a simplification of what's happening and there are reasons to increase spoke tension in certain circumstances but unless your wheel is out of true or some of the spokes are loose I would avoid messing with them.


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## Ajax Bay (4 Oct 2019)

overmind said:


> I was looking at some wheels in the bike shop yesterday and noticed that the more expensive high-end wheels have much higher spoke tension. What is the reason for this? I've noticed the spokes on my bike (BTwin Triban 3) are tight but not as tight as this.
> Would there be any benefit in tightening my spokes? Say, 1/4-1/2 turn all round the wheel and then re-true?


How did 'looking at the wheels' allow you to 'notice' that the spoke tension was higher, please? I'll go for a 'no'.


si_c said:


> If you think about the wheel as a system and the total tension of all the spokes required to keep a wheel circular and true then divide by the number of spokes and you will immediately see the need for greater tension. This is a bit of a simplification . . .


Why does the total tension (presumably you mean adding the tension of all the spokes together) need to be the same? This implies that a 16 spoke wheel wIll have twice the spoke tension of a 32 spoke wheel. I pity the rim of that 16 spoke wheel. If this question is too simple, please share the complexities with us.


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## si_c (4 Oct 2019)

Ajax Bay said:


> How did 'looking at the wheels' allow you to 'notice' that the spoke tension was higher, please? I'll go for a 'no'.
> 
> Why does the total tension (presumably you mean adding the tension of all the spokes together) need to be the same? This implies that a 16 spoke wheel wIll have twice the spoke tension of a 32 spoke wheel. I pity the rim of that 16 spoke wheel. If this question is too simple, please share the complexities with us.


It doesn't need to be be the same in the way you are implying but for a given rider weight there needs to be enough strength in the system to counteract the load (Force) on the wheels. Reducing the number of spokes increases the amount of load that each spoke will account for - this is complicated by the fact that not all spokes are evenly loaded as the wheel goes around.

I do have a rudimentary understanding of how this works, but I'm not an engineer and I know what I don't know, so at this point I'm going to bail and page @Yellow Saddle who will no doubt point out where I've gone wrong above anyway


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## Spoked Wheels (4 Oct 2019)

overmind said:


> I was looking at some wheels in the bike shop yesterday and noticed that the more expensive high-end wheels have much higher spoke tension. What is the reason for this? I've noticed the spokes on my bike (BTwin Triban 3) are tight but not as tight as this.
> 
> Would there be any benefit in tightening my spokes? Say, 1/4-1/2 turn all round the wheel and then re-true?


Cheap factory wheels tend to come with under tension straight spokes. Higher end wheels tend to come with better spokes, more spokes tension and fewer spokes too.



overmind said:


> Does that mean that the buckle was there to begin with? Otherwise what would have caused the buckle (if it was not doing wheelies)?



It's possible that it was there and it got worse. My guess is that your spokes were under tension and made the wheel weak.

My son's mate rode his new bike down a mountain and the rear wheel was unridible afterwards, I was with them and with my spoke key I straightened the wheel enough for him to ride home... but the spokes were very under tension.


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## Ajax Bay (4 Oct 2019)

si_c said:


> for a given rider weight there needs to be enough strength in the system to counteract the load (Force) on the wheels. [1] Reducing the number of spokes increases the amount of load that each spoke will account for [2] - this is complicated by the fact that not all spokes are evenly loaded as the wheel goes around.[3]


1. Agreed but. Assuming a 100kg load (rider and bike) and an even split rear/front (it's not) that means the load on the wheel is 490N (50kg x g).
2. Even (in a notional very low spoke wheel) if only one spoke is taking the reduction in load (tension) the reasonable spoke tension of 1000N will only reduce by 490N. So that spoke is still at 500+N tension. In practice in a 16 spoke wheel the spokes adjacent to the 'lowest' one are sharing some reduction in load (equal in total to the load on the wheel). (See also the quote below.) If a the spokes in a wheel are 'under-tensioned' (as @Spoked Wheels has described) then there's a danger of the the force on the wheel over-matching the spoke tension, with adverse effect (potential for spoke nipples to loosen and the wheel to lose true).
3. If you have not read pages 3 and 4 of this thread, the discussion there tries to consider and understand the way tension in spokes vary as the wheel (under load) rotates.


Ajax Bay said:


> So as this (model front) wheel rolls, the spoke tension cycles between (slightly over) 1000N (when horizontal) through 880N down to 740N and back up. The more spokes in a wheel the less reduction (%) the lowest spoke experiences. Will the magnitude of the cyclical range of tensile force in a spoke be related to fatique life? Probably (intuitively), but I don't know.


This Wjeelfanatyk article seemed relevant to me, to help inform the answer to @overmind 's question.
ETA this image: https://www.wheelfanatyk.com/wp-content/uploads/2014/01/tension-crank.jpg


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## Ming the Merciless (4 Oct 2019)

No, there's quite a wide range of spoke tension under which a wheel will remain strong and true. Once you are in this range, increasing the tension does not make the wheel stronger.


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## MichaelW2 (4 Oct 2019)

As I understand it, spokes should be tight enough so they never operate in compression during the heaviest loading ( eg big rider hitting a bump). Once spikes lose tension for a moment the no longer contribute to the strength of a wheel during that moment.


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## Yellow Saddle (4 Oct 2019)

si_c said:


> It doesn't need to be be the same in the way you are implying but for a given rider weight there needs to be enough strength in the system to counteract the load (Force) on the wheels. Reducing the number of spokes increases the amount of load that each spoke will account for - this is complicated by the fact that not all spokes are evenly loaded as the wheel goes around.
> 
> I do have a rudimentary understanding of how this works, but I'm not an engineer and I know what I don't know, so at this point I'm going to bail and page @Yellow Saddle who will no doubt point out where I've gone wrong above anyway


I think your understanding is correct except for the concept of "total tension doubled". The total tension in a 16-spoke wheel is not as high as that of a 32-spoke wheel, It simply cannot be because spokes are already loaded at the upper end of their tensile strength and, that would put an enormous amount of tension on sparsely-spaced spots on the rim. In short, it is just about impossible to double the tension of some spokes in a wheel. Typically, I'd build a 32-spoke wheel with about 1500N on the right hand spokes. To double it would imply 3000N. At that tension the nipples will not turn, the spoke will rotate with the nipple, the rim will burst and your fingers will fall off.

A 16-spoke wheel does require higher tension, but not double. It makes up for the lack of "double tension" at a spoke by spreading the load-affected zone wider, through the use of a sturdier rim. Some rims, especially deep section rims are super stiff compared to box section rims. I used to sit on deep sections (35mm and up) and bounce, with no ill effect, whereas I once sat on a Mavic MA 2 with, lets say, I'll effects. This demonstrates how a deep section employs a very large load effected zone that can accommodate enough spokes to make up for loss of individual tension.

That's a bit long-winded and inelegant, but the best I can squeeze out now.


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## Yellow Saddle (4 Oct 2019)

Ajax Bay said:


> The more spokes in a wheel the less reduction (%) the lowest spoke experiences. *Will the magnitude of the cyclical range of tensile force in a spoke be related to fatique life? Probably (intuitively), but I don't know.*
> The spokes fatique and eventually, when @hobo gives that last push, the rear wheel spoke that happens to be weakest parts. On my ride last week each of my spokes (36 spoke front wheel) went through this cycle (1000N to >800N) over 100,000 times. Last year the spokes in my front wheel which I built it in Jan 18, completed this cycle over 5 million times. I used the original spokes from the fubarred wheel (rim) so I estimate these spokes have completed 20 million cycles with me aboard (plus no idea how many with the first owner on board). Pleased to say no front spokes broken yet.



This quote is a year old, forgive me for re-hashing it. I think it bears relevance to the entire discussion. I've put the important question in bold.

The answer is yes, the cyclical range does have an effect on fatigue life (sometimes called Endurance Limit or even Fatigue Strength). Steel has a fatigue limit, which means that cyclical changes in stress have no effect on the fatigue life of the piece. In short, it means that if the changes are kept below a certain level, then the material effectively an infinite life. This limit ranges a bit and can be as high as 35% of tensile strength or as low as 65% of tensile strength.

We can relate back to spokes. A 1.8mm spoke has a tensile strength of about 2400N. Typically, we build to no more than 1500N and the cycles will be (big approximation here) about 200N. Even with a high limit of 35% you can see that a wheel can easily be built with infinite spoke life.

The important factors are: enough spokes; stiff enough rim and proper stress relieving.

Unfortunately, rims, made from aluminium, has a fatigue limit and it is pretty low too. Rims therefore crack long before spokes break, if the wheelbuilder knows his onions.

Edit: An error was pointed out to me and I've changed the magnitude of cyclical changes from 20N to 200N. The demonstration remains valid.


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## Dogtrousers (4 Oct 2019)

Yellow Saddle said:


> Unfortunately, rims, made from aluminium, has a fatigue limit and it is pretty low too. Rims therefore crack long before spokes break, if the wheelbuilder knows his onions.


In my experience neither happens. Rather the braking surface wears out before the rims crack or the spokes break.

This may be because I've been lucky and/or my wheels have been built by an alliumologist. 

Or maybe it's because I and my bike are such dainty featherweights we don't stress the wheels.


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## Ian H (4 Oct 2019)

Dogtrousers said:


> In my experience neither happens. Rather the braking surface wears out before the rims crack or the spokes break.
> 
> This may be because I've been lucky and/or my wheels have been built by an alliumologist.
> 
> Or maybe it's because I and my bike are such dainty featherweights we don't stress the wheels.



It's cos you brake too much. To quote a very eminent green-clad cyclist: "Brakes are for emergencies only!"


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## Yellow Saddle (5 Oct 2019)

Dogtrousers said:


> In my experience neither happens. Rather the braking surface wears out before the rims crack or the spokes break.
> 
> This may be because I've been lucky and/or my wheels have been built by an alliumologist.
> 
> Or maybe it's because I and my bike are such dainty featherweights we don't stress the wheels.


Of course it is perfectly plausible that the brake surface wears out before the alu cracks. In dry countries, wheels fail from aluminium fatigue. In wet countries, from rim wear. There are plenty of variations in-between, including terrain and traffic, all which has bearing on how much you brake.


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## rogerzilla (6 Oct 2019)

I've just broken a spoke on the track bike. 16 years on the road and occasionally the velodrome, including my entire racing career, and it was a crap unbranded set that came with a Fuji Track and which I reused, Scrooge-like, when I swapped the original hub for a Goldtec in...er...2004. I'm not too ashamed, especially as it broke after this year's Dunwich Dynamo (which no doubt finished it off).

I'll rebuild the wheel with DT Competition spokes. The rim is, of course, as new since it's never known the kiss of a rear brake.


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## Dogtrousers (7 Oct 2019)

Ian H said:


> It's cos you brake too much. To quote a very eminent green-clad cyclist: "Brakes are for emergencies only!"


If you're racing for a green jersey, maybe. If you're riding in London, emergencies tend to crop up every 100m or so.


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## Ian H (7 Oct 2019)

Dogtrousers said:


> If you're racing for a green jersey, maybe. If you're riding in London, emergencies tend to crop up every 100m or so.


Nev didn't race much. Long-distance touring was his forté. But always in Evesham green.
Emergencies? Sounds like a lack of anticipation.


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## Flying Dodo (14 Nov 2019)

Ian H said:


> Nev didn't race much. Long-distance touring was his forté. But always in Evesham green.
> Emergencies? Sounds like a lack of anticipation.


In London, it's impossible to anticipate the idiots around you. There's too many of them.


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## Ian H (15 Nov 2019)

Flying Dodo said:


> In London, it's impossible to anticipate the idiots around you. There's too many of them.


That hasn't been my experience over several decades of urban riding in London and other cities.


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## Nigelnightmare (26 Dec 2019)

Assume that every other road user is a complete idiot & out to get you and you won't be far wrong + you'll probably live longer too.


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## preventec47 (31 Oct 2020)

This is an old thread so i wont go into great detail but everyone interested should google Metal Fatigue and Endurance Limit etc.
This spoke situation is EXACTLY the same as rod bolts in a piston rod in a motor. If the bolts are not torqued to a sufficiently tight
"stretch" beyond the endurance limit then with every rotation of the motor, one more stress cycle is added to the bolt until
it reaches its fatigue life and fails. however, it the bolt is stretched to beyond the endurance limit then each engine cycle does
NOT cause the rod bolt to cycle above and below the fatigue limit with each engine rotation which adds to the cycles leading to failure.
SO, loose or non sufficiently tight spokes DO fatigue but sufficiently tight spokes will NOT accumulate fatigue cycles toward failure.
To clarify further, NO movement is needed to create fatigue. ONLY stress and de stress to and past the endurance PSI limit and back under is needed to cause weakening of metal until a failure occurs at a MUCH less tensile strength than what the original metal was
rated for.


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## raleighnut (31 Oct 2020)

preventec47 said:


> This is an old thread so i wont go into great detail but everyone interested should google Metal Fatigue and Endurance Limit etc.
> This spoke situation is EXACTLY the same as rod bolts in a piston rod in a motor. If the bolts are not torqued to a sufficiently tight
> "stretch" beyond the endurance limit then with every rotation of the motor, one more stress cycle is added to the bolt until
> it reaches its fatigue life and fails. however, it the bolt is stretched to beyond the endurance limit then each engine cycle does
> ...


Billhooks, I've got wheels 30 odd years old,


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## Ajax Bay (1 Nov 2020)

@preventec47 
I've tried to recast your contribution - hopefully I've got it right enough.

"i wont go into great detail
google Metal Fatigue and Endurance Limit etc.
If spokes . . . are not tensioned/stressed to cause a "stretch" beyond the endurance limit then with every rotation of the wheel is one stress cycle (for each spoke in turn) until it reaches its fatigue life and fails.
If the spoke is stretched to beyond the endurance limit then each wheel cycle does NOT cause the spoke tension to cycle above and below the fatigue limit so this doesn't add to the cycles leading to [fatigue] failure.
SO, insufficiently tight spokes DO fatigue but sufficiently tight spokes will NOT accumulate fatigue cycles toward failure.
To clarify further, NO movement is needed to create fatigue. ONLY stress and de stress to and past the endurance limit and back under is needed to cause weakening of metal until a failure occurs"

Perhaps you could jump to the 'so what'? What are you suggesting will happen in practice?
You say "sufficiently tight spokes will NOT accumulate fatigue cycles toward failure" That a properly tensioned/tight spoke never fatigues? Or what?
A spoke (say plain gauge 2mm diameter) has a cross section of 'Pi'mm2. It's under tension of (say) 1000N so about 318N/mm2. "A simple rule of thumb calculation for the fatigue limit is one-half of the ultimate tensile strength " which for stainless steel (material of spokes) seems to be in the region of 500N/mm2. Half that is 250N/mm2. So properly tensioned spokes are above the fatigue limit of their material.
[A MPa = 1N/mm2]
On my long ride last week each spoke was cycled from its normal 'rest' (stationary) stress to maybe 200N less (32 spoke wheel), and back to normal more than a quarter of a million times.
After many millions of cycles I expect the first spoke (rear wheel, right side) to fail through fatigue. Before then it's highly likely I'll have replaced the rim (caliper brakes) and likely used a new set of spokes to lace the new rim up.
Do you think a bicycle's spoked wheel rim moves radially as it rolls, with a (rider) load?


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## rogerzilla (15 Jan 2021)

The left spokes usually go first on a rear wheel, because they can't be tightened enough without massively overtightening the right spokes (and either splitting the nipples or damaging the rim).


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## Ajax Bay (15 Jan 2021)

rogerzilla said:


> The left spokes usually go first on a rear wheel, because they can't be tightened enough without massively overtightening the right spokes (and either splitting the nipples or damaging the rim).


Left spokes can be tightened "enough" . . . "without massively overtightening the right spokes". Every properly tensioned rear wheel has spokes like this. Every rear wheel with under tensioned spokes can be remediated so the spokes are tensioned and the rim is true, without overtightening the right spokes. Sorry I either don't understand what you are trying to say, or I don't agree, but persuade me.
Why would rear wheel left hand spokes (at a lower tension than the right hand spokes) fail (presume though fatigue) "first"? Both sets of spokes are going though the cycle of 'lower tension' as their bit of rim is at 6 o'clock but every spoke stays in tension throughout (see upthread).
I think we had established upthread (a few pages for you to check) that the spokes that have to work hardest (and tend to be the earliest to fail if the rim doesn't go first) are the trailing spokes on the right hand side, because they are at a higher tension and they have additional stress from the torsional load from the drive train. I remember asking this specific question - was it in 2019?


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## rogerzilla (17 Jan 2021)

The left hand spokes can't always* be tightened enough to prevent them going completely slack when you hit a bump; the lowest one may be perilously close to zero tension when just riding along, if you're fairly heavy and the rim can't take a very high average tension. The RH spokes are prone to mauling from an unshipped chain but otherwise have a better chance, since they never get anywhere near slack and the variation in tension when riding, as a proportion of initial load, is much smaller. Spokes don't break because they are too tight. The difference between leading and trailing spokes isn't massively important on a wheel with a rim brake, and builders can never agree on which side of the flange they should go (I like the "pulling" spokes to be heads-in, since they're better-braced, but some people insist they should be heads-out to pull the spokes clear of the rear mech cage on climbs!).

Derailleur wheels are a horrible compromise, really. A dishless wheel, such as you get on a fixie, singlespeed and on some IGH hubs, gives far less trouble but you just can't have one with 11 speeds (or even 7) and the usual 130mm spacing. That spacing can't be increased much further because your feet end up too far apart at the pedals.

*DT Revolution or other thinner, stretchier, spokes, are good on the LH side because they are more able to retain tension under a big shock load; they stretch by 0.5-1mm when tensioned.



Ajax Bay said:


> A spoke (say plain gauge 2mm diameter) has a cross section of 'Pi'mm2. It's under tension of (say) 1000N so about 318N/mm2. "A simple rule of thumb calculation for the fatigue limit is one-half of the ultimate tensile strength " which for stainless steel (material of spokes) seems to be in the region of 500N/mm2. Half that is 250N/mm2. So properly tensioned spokes are above the fatigue limit of their material.


Spokes are drawn and therefore much stronger than plain stainless material. A Sapim Race spoke has a strength (they don't say what, but it's usually yield strength, not UTS which is even higher) of 1300 N/mm^2. So my 150kgf spokes aren't anywhere near that, at about 580N/mm^2.


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## Ajax Bay (17 Jan 2021)

rogerzilla said:


> The left hand spokes can't always* be tightened enough to prevent them going completely slack when you hit a bump; the lowest one may be perilously close to zero tension when just riding along


Roger - before I invite you to share a link to anyone else who says something along these lines, please could you confirm you've read this thread from start to finish. I think we have tried to quantify, very roughly, the sort of tension changes which might occur in the lowest spokes as they roll through.
On one of your well built rear wheels might the tensions be 1000N on the left side and 1500N on the right? A rear wheel under a heavy rider might experience a rolling load of 700N. So even if ONLY one spoke reduced in compression by that amount the spoke would stay in tension: is 300N 'perilously close'?
In practice several spokes would be taking part of the load (at least 3 even on a 20 spoke wheel) so the residual tension would be well more than 300N. A heavy rider would be well advised to choose a rear wheel with a decent number of spokes and a rim which can be built into a robust wheel.
So positing a heavy rider and a rim which "can't take a very high average tension" is a strawman - in the context of 'can't get the left hand spokes tensioned enough'. Surprised you didn't add in "low spoke count" to make it a target really easy to punch.
On the material properties of a Sapim Race spoke, I think you are agreeing with me "properly tensioned spokes are above the fatigue limit of their material" ie eventually, in normal use, they will fail through fatigue - thank you.


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## rogerzilla (18 Jan 2021)

Ajax Bay said:


> On the material properties of a Sapim Race spoke, I think you are agreeing with me "properly tensioned spokes are above the fatigue limit of their material" ie eventually, in normal use, they will fail through fatigue - thank you.


Er...no. Even my very tight spokes aren't stressed to 50% of Sapim's quoted strength (which I believe is yield, not UTS).

Rims are usually quite stiff these days, but older rim designs (and some that you can still buy, I'm looking at you, Mavic) will elastically pringle well before the spokes are as tight as you would like. In fact, this used to be the way to determine optimal tension: get to the pringle, then back off every spoke by a half a turn to a turn. In these cases, the LH spokes can be alarmingly slack, maybe 50kgf, and prone to losing all tension very easily. The 18 LH spokes on my rear touring bike wheel (built by, allegedly, one of the UK's best wheelbuilders) are all over the place tensionwise but many are a mere 60kgf, which probably explains why it went out of true easily. The 16 LH spokes on my race bike are 100-110kgf, which is more like it.


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## Ajax Bay (19 Jan 2021)

I erred when I asserted that "properly tensioned spokes are above the fatigue limit of their material". They aren't. Thank you for picking me up on that.
Still think your strawman (heavy rider, weak/poor rim) in the context of 'can't get the left hand spokes tensioned enough' is not useful, except as an outlier.
@Yellow Saddle 's post provides detail.
"the cyclical [stress] range does have an effect on fatigue life (sometimes called Endurance Limit or even Fatigue Strength). [But] steel has a fatigue limit, which means that cyclical changes in stress have no effect on the fatigue life of the piece: if the changes are kept below a certain level, then the material effectively has an infinite life. This limit varies a bit and can be as [low] as 35% of tensile strength or as [high] as 65% of tensile strength.
"We can relate back to spokes. A [example double butted 2.0/1.8mm] spoke has a tensile strength of about 2400N. Typically, we build to no more than 1500N and the cycles will be (big approximation here) about 200N. Even with a [high fatigue] limit of 35% [of tensile strength] you can see that a wheel can easily be built with infinite spoke life.
"The important factors are: enough spokes; stiff enough rim and proper stress relieving.
"Unfortunately, rims, made from aluminium, have a fatigue limit and it is pretty low too. Rims therefore crack long before spokes break, if the wheelbuilder knows his onions.[/QUOTE]


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## rogerzilla (19 Jan 2021)

Yellow Saddle is right, and it's perfectly ok to re-use spokes when a rim wears out (I use new nipples, since they cost peanuts) since they will go on indefinitely if built properly.

Caveat: cheap unbranded spokes can break even in a good wheel. The top branded spokes (DT and Sapim) are vastly better than they were in the 1970s or earlier but OEM wheels may use nastier ones. I broke a spoke on my track bike last year; it was a no-name set of spokes that came on a 2003 Fuji Track and was on its second hub (!) and rim. I felt cheated.


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## T4tomo (13 Apr 2021)

I know nothing about wheel building so here is a question for the experts....

I have a broken spoke on a wheel from 1987, original spokes as far as I can tell. Hubs and rims are fine and the bike doesnt get a lot of use - its special occasions ride. Spoke tension appears to be be all over the place, do i just get the one spoke replaced or should i ask him to rebuild both wheels with new spokes. Apart from new spokes looking nice and shiny (which is definitely a consideration) is it generally a good idea to replace 34 year old spokes?


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## Ajax Bay (13 Apr 2021)

This non-expert would opine: replace the spoke and get the spoke tensions evened up and taught. Ride on. This assumes the current spokes are stainless steel, you can't see the spokes' threads at all (ie inside the nipples, therefore right length) and that you've had the wheel from new so you know it has done very limited mileage. Rear wheel, right side?


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## T4tomo (13 Apr 2021)

I've not had bike or wheel from new. 
Broken spoke is rear non drive side.


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## Ajax Bay (13 Apr 2021)

In that case I would still replace one spoke and tighten/balance up generally (pings the same tone on the left side and higher on the right). If another one goes, that suggests that they (all xx spokes) are reaching their fatigue life limit (having done an unknown number of miles under their previous owner(s)). More will follow. Relace, after a careful check of every rim spoke hole for cracks.


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## Punkawallah (31 May 2021)

So, his successive failures are a result of ‘old age’?


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## Ajax Bay (31 May 2021)

I said: "If another one goes, that suggests that they (all xx spokes) are reaching their fatigue life limit (having done an unknown number of miles under their previous owner(s)). More will follow."


Punkawallah said:


> So, his successive failures are a result of ‘old age’?



@T4tomo has only had one spoke part, so these are not "successive failures"; and that's important. To adapt Goldfinger's 'happenstance, coincidence, enemy action' assessment:
Happens once: replace.
Repeat occurrence: indicator that the set of spokes are reaching their fatigue life. (NB this is not "old age"; the variable is not time but tension cycles (millions)). The set of individual spokes will have a range of cycle fatigue limits with a distribution which could be Gaussian. One may go for a reason other than fatigue (eg physical damage), but once the second goes, the risk of just replacing only that one is that a third will go shortly, to the detriment of an enjoyable ride. Bit akin to identifying a lesson, but then not learning it.
HTH


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## Punkawallah (31 May 2021)

Thanks for that :-) Every day’s a school day! Think I was commenting on an earlier post than the one you referenced, still getting used to this whole ‘Interweb’ thing. Serves me right for not checking :-)
Not an engineer, so happy to work with ‘old age’ and ‘fair wear & tear’ without looking to ’gotcha’ 👍

While I have you, Gaussian distribution?


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## lane (31 May 2021)

GT grade spokes kept breaking. I was told poor quality rims and when I googled the rims quite a few with same issues. Spa built wheels decent rims no more breakages.

It wasn't fatigue with the Grade not done many miles.


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## Ajax Bay (31 May 2021)

lane said:


> GT grade spokes kept breaking . . . it wasn't fatigue


Absolutely. Spokes sequentially breaking after a long rolling life indicates fatigue limits being hit (and a relacing required). Before that it's a wheel building issue.
Have a read of this thread: https://www.cyclechat.net/threads/gt-grade-stans-grail-spoke-problem.220652/ to which @I like Skol contributed.


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## lane (31 May 2021)

Ajax Bay said:


> Absolutely. Spokes sequentially breaking after a long rolling life indicates fatigue limits being hit (and a relacing required). Before that it's a wheel building issue.
> Have a read of this thread: https://www.cyclechat.net/threads/gt-grade-stans-grail-spoke-problem.220652/ to which @I like Skol contributed.



Thanks interesting thread. My GT Grade was stolen so that solved the problem in a way.


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## ConnoisseurEquator (16 Aug 2021)

Hi
Sorry to revive that thread but I have a problem similar with my 40yo Raleighs.
2 spokes broke on both of them during the last few months. 
Both have a hub with a Dyno 3 speed.
I tried to replace 3 of them when I realised that the 4th broke. I don't know when it did actually.
Is it ok to replace them with similar spokes taken from other wheel? 
Well one.
They are not the same size by 1-2 mm, so I cut them.

I also notices that the wheel are not perfectly true [? ]. A bit of a spine curved. I noticed it while fixing the brakes pads.
I YouTubed them but the explanation is as clear as a muddy water to me.
If its bend to one side, screw the other side. Not really conclusive.
I tend to do everything on all my 3-4 speed bikes. More recently as I have more time on my hands. 
Any ways to understand this jargon a bit more easily?
Thanks


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## Ming the Merciless (16 Aug 2021)

See https://bikemagic.com/how-to/mountain-bike-maintenance/wheel-truing-basics.html


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## Ajax Bay (16 Aug 2021)

My advice would be (and I have tried to keep a rear 1980 wheel alive):

If you're getting sequential spoke failure then these are the first few (4!) failing from fatigue and the rest will be on their way, potentially spoiling multiple rides.
Bite the bullet and replace all the spokes you haven't already replaced (eg 28?).
If you do them one by one, you can tighten each spoke so it 'pings' the same note as its mates and that will get you to a start point for truing the wheel (see the Merciless one's link above).
If you know the wheel you're stealing a spoke from has done little mileage you can treat it, for fatigue life, as new.
Your LBS (assuming it's good) will have spokes the right length to sell you.
Shortening spokes which are bit too long will not result in them being weaker per se, but remember you are reducing the number of engaged threads. A couple of mm: OK.
Using spokes which are too short risks the same but also in addition risks the rolled thread showing the hub side of the nipple, and that can result in a stress riser exposed to the elements.
HTH


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## rogerzilla (27 Aug 2021)

Short spokes are especially bad in alloy nipples, as the nipple needs to be full of spoke thread up to the bottom of the screwdriver slot, otherwise it can just snap in half.


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## Ajax Bay (15 Feb 2022)

Thought this was a neat image, in the context of wheels standing on the lower spokes or hanging on the upper spokes, or neither.


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## Carpathian Rider (4 Sep 2022)

Hi,
Let me to ask my question here, suppose it's relevant thread.
Week ago during mountain ride my rear wheel was broken and rim aquired the curvature wich incompatible with further riding.
So, was decided to replace a rim and the spoke set. Appropriate rim an spokes already bought, but when I start lacing the spokes, noticed that effective rim dia ERD in fact a little more, than specified by manufacturer (2-3 mm more).
I confused, and need to replace at least 18 spokes at longer side.
Does anyone have similar experience with misunderstanding between specified ERD and actual one?
Or may be some vendors have alternative way to determine this parameter. Looks like in my case manufacturer determine ERD as imaginary diameter on eylets top sides.
But according to most material found in net ERD is determined as imaginary diameter touches the ends of fully threaded spokes (when the end of spoke located around the bottom of nipple slot).


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## Ajax Bay (5 Sep 2022)

So 36 spoke wheel. How long were the right and left side spokes?
Make/model of hub? Make/model of rim?


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## Jameshow (5 Sep 2022)

Erd from manufacturers are often a stab in the dark tbh.

Usual practice is to measure yourself using 2 spokes or inside the rim +3-4mm 

if the spokes are a little short the tensioning if them will normally pull them into a reasonable length.


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## Carpathian Rider (5 Sep 2022)

Rim - Mach1 Road Runner http://www.mach1.fr/en/rims/road-runner-44 
ERD 591 according to mfr spec.
Hub - old type Novatec, 50mm both flanges dia.
Spoke length was calculated here https://spokecalculator.qbp.com/spokecalculator/calculate and checked on another sites.
Calculation sheet:




So, for state-of-the-art 3 cross lacing was decided to use just 1 length set - 283mm DT Swiss Competition (bought from private persone, but looks original with stamp)
But in fact calculator's ERD is determined according to following picture 


and mfr ERD obviously specified by another way, may be on the top of eyelets.
As expected, short side spokes still compatible (just 2-3 turns of thread are visible under the nipple skirt, suppose it enough engagement), otherwise longer side have quite poor engagement. 
Currently waiting for another 20pcs 286mm spokes for longer side replacement.
And stay confused, why the manufacturers still not have uniform ERD measurement system
But for future it will be good lesson to buy rim at first, measure by youself and then buy spokes.


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## Jameshow (5 Sep 2022)

I'd be surprised you could use one spoke length normally I'd use 2/3 front, nds and drive side??


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## Carpathian Rider (5 Sep 2022)

Jameshow said:


> I'd be surprised you could use one spoke length normally I'd use 2/3 front, nds and drive side??



When you have calculated lengths difference about 1.5mm for driver side and non driver side, it's possible to use one length for both sides.
But due to real ERD become bigger than mentioned, only driver side have acceptable length.
Speech is only about rear wheel.


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## Ajax Bay (6 Sep 2022)

Carpathian Rider said:


> As expected, short side spokes still compatible (just 2-3 turns of thread are visible under the nipple skirt, suppose it enough engagement), otherwise longer side have quite poor engagement.
> Currently waiting for another 20pcs 286mm spokes for longer side replacement.


Really annoying to get the 'wrong' ERD for the rim from the supplier.
Allow me to remark that if there is thread visible 'below' the nipple the spoke is not long enough (rule of thumb). Or are they threaded more than 'normal' - in which case you need longer nipples. Threads showing like that are potential stress risers.


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## Carpathian Rider (11 Sep 2022)

Actually, the problem was fixed. Non driver side spokes was replaced and all nipples was changed into longer ones.
So, all threads are hidden by nipples. 
@Ajax Bay , thanks for advise about visible threads


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