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

[ConnoisseurEquator]

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

 

[Ming the Merciless]

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

 

[Ajax Bay]

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

 

[rogerzilla]

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.

 

[Ajax Bay]

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

 

[Carpathian Rider]

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).

 

[Ajax Bay]

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

 

[Jameshow]

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.

 

[Carpathian Rider]

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.

 

[Jameshow]

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

 

[Carpathian Rider]

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.

 

[Ajax Bay]

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.

 

[Carpathian Rider]

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

 

[silva]

My older/previous bike, since 2 weeks in use due to avatar bike now a pile parts without frame, last sunday a loose sitting spoke. I could pull the nipple out the rim and it looked like broken in 2 pieces, one screwed on the spoke, the other sitting at the other side of the inner wall.
Today I lifted 1 side of the Marathon Plus painintheasstodothat tyre over the rim edge to get the other part of the nipple out.

I saw the rim had a steel kinda "inserts" at every nipple hole, all showing rust.
During the 10 years i used the bike daily, I have had a dozen spoke breaks, but never a nipple.
What is recommended here, just a new nipple, a new nipple + new spoke, or a new rim due to the rusty steel inserts?
Because, that may have inflicted some corrosion on, I assume-stainless steel nipples, which can prevent the stainless from recreating its protective oxidation layer, causing the nipple to rust, and to end up breaking at the contact place with the non stainless steel of the inserts, risking in the future breaks of further nipples.

Another question, when I compare the spoke tension of my travelbike wheels, the average tension of the wheels for this older/previous bike is clearly less, the spare wheel I mounted, despite its state of not having been used since returned from dealer for maintenance. Why this tension difference?

 

[Ajax Bay]

What is recommended here, just a new nipple, a new nipple + new spoke, or a new rim due to the rusty steel inserts?

New stainless steel spoke. New brass nipple.
[Take care when googling.]
See this thread for more: https://www.cyclechat.net/threads/rusty-nipples-ok-corroded-but-wheres-the-drama-in-that.198848/
I'd be rather surprised if the eyelets on your rim were steel. So the 'rust' you report is not from those.
A magnet is your friend.
Consider replacing all the nipples with brass ones, while you have the tyre off.

https://www.customcutspokes.co.uk/product-category/bicycle-spoke-nipples/14g-spoke-nipples/
https://sheldonbrown.com/wheelbuild.html
"Many good quality rims have "eyelets" or "ferrules" to reinforce the spoke holes. The best double-wall rims have sockets which spread the load to both layers, allowing these rims to be lighter and/or stronger."

Rim without eyelets	Rim with eyelets	Rim with recessed spoke holes and no eyelets	Rim with recessed spoke holes and eyelets	Socketed rim with eyelets
Rim cross-sections