Broken Spokes - When to give up on a wheel?

[EasyPeez]

Hi,

I'd never had a broken spoke in my life until late last year. Now I've had 3 in 3 months. Does this suggest it's time to get a new wheel or should I persevere with getting on spoke at a time changed? I'm only 10stone in weight and carry a backpack with a few bits in, so not sure why this is happening all of a sudden?

I am riding a 14 year old £200 MTB that has been stuck in a shed for the last few years doing very little, then getting hammered 15miles+ a day on bad roads in all weathers and jumping off kerbs etc every day since last summer. So I guess maybe cheap wheels + long period of abuse (I never used to clean or lube it at all I'm ashamed to say - ironically I'm doing that weekly now and it's only now that the problems have started!) + long period of disuse + lots of hammer = this is inevitable? Or could it be something myself or my LBS is doing wrong?

I'd like to learn how to fix this myself this year, but for now I have neither the required tools or know-how, so have been getting my LBS to do it. Could it be that they're not truing it properly after fitting new spokes, hence the continued breakages?

I'm picking up my new Genesis at the weekend (weather permitting) so if there's anything I can do (other than look after it a whole lot better!) to avoid similar problems with that bike please let me know!

Cheers, Andy

 

[Yellow Saddle]

The spokes are breaking because they're experiencing metal fatigue. Have someone rebuild the wheel with new spokes and make sure they know how to stress-relieve the wheels. It has nothing to do with maintenance or curb jumping or long periods of disuse. They were crappy spokes on an entry-level bike and therefore had a limited lifespan, which incidentally is measured in wheel revolutions, not time.

 

[User6179]

3 and I bin the wheel unless the 3 spokes are all the same , for example all trailing spoke on NDS then I would just change the other 5 ( on 32 spoke wheel) of the same type .

 

[Yellow Saddle]

3 and I bin the wheel unless the 3 spokes are all the same , for example all trailing spoke on NDS then I would just change the other 5 ( on 32 spoke wheel) of the same type .

You would only be fooling yourself should you do this. All the spokes on the left and all the spokes on the right undergo the same strain and cyclical stresses. Once three spokes in a wheel have broken, you can be sure that the rest will break too, no matter where they are. Replace and forget.

 

[User6179]

You would only be fooling yourself should you do this. All the spokes on the left and all the spokes on the right undergo the same strain and cyclical stresses. Once three spokes in a wheel have broken, you can be sure that the rest will break too, no matter where they are. Replace and forget.

Not so , I did exactly this on my CX bike and had no more broken spokes , I have did 500 miles plus since changing the rest of the spokes .

 

[Hip Priest]

I used to have spokes break all the time and thought it must be my weight causing it, but then I got some better wheels and the problem went away. You don't have to break the bank. I've done 3500 miles on my Shimano R500s and they're still true.

 

[Yellow Saddle]

Not so , I did exactly this on my CX bike and had no more broken spokes , I have did 500 miles plus since changing the rest of the spokes .

One anecdote doesn't override the science behind this. Besides, 500 miles is very little and just exposes the small variances in the spokes.

Your suggestion is essentially to look which spokes break and then decide whether or not to replace the outbound or inbound series on that side of the wheel. The only differences between outbound and inbound spokes is that the former are bent at an acute angle at the heads and the latter at an obtuse angle. The difference is a few degrees either side of 90. Once these spokes have been tensioned and stress-relieved, the base-line for fatigue is the same and effectively they both start at Zero. Once the wheel is in use, the strain (the change in length per wheel revolution) is the same for both the series and therefore fatigue remains the same. The only reason spokes don't all break at exactly the same reason is randomness. Not all cars of the same make will have their cambelts breaking at exactly 100 000 kms or such.

Anecdote is not science. The fact that my grandfather smoked 90 cigarettes a day and died in his 70s doesn't prove that tobacco is healthy.

 

[pclay]

I used to have spokes break all the time and thought it must be my weight causing it, but then I got some better wheels and the problem went away. You don't have to break the bank. I've done 3500 miles on my Shimano R500s and they're still true.

^This.

That paragraph is the same for me. running on R500s for about 8 months now, and still true.

 

[EasyPeez]

Have someone rebuild the wheel with new spokes and make sure they know how to stress-relieve the wheels.

I'll ask the chap I know in the LBS if this is within his skill-set. But for the time/labour that's going to involve, and given that we're talking about a pretty crappy wheel here on a bike that is soon to become my second bike for use only in bad weather, wouldn't it be cheaper to buy a bottom-end new wheel for it?

 

[User6179]

One anecdote doesn't override the science behind this. Besides, 500 miles is very little and just exposes the small variances in the spokes.

Your suggestion is essentially to look which spokes break and then decide whether or not to replace the outbound or inbound series on that side of the wheel. The only differences between outbound and inbound spokes is that the former are bent at an acute angle at the heads and the latter at an obtuse angle. The difference is a few degrees either side of 90. Once these spokes have been tensioned and stress-relieved, the base-line for fatigue is the same and effectively they both start at Zero. Once the wheel is in use, the strain (the change in length per wheel revolution) is the same for both the series and therefore fatigue remains the same. The only reason spokes don't all break at exactly the same reason is randomness. Not all cars of the same make will have their cambelts breaking at exactly 100 000 kms or such.

Anecdote is not science. The fact that my grandfather smoked 90 cigarettes a day and died in his 70s doesn't prove that tobacco is healthy.

I appreciate your knowledge on the matter but when 3 spokes all trailing on NDS break over a 1000 miles then it is maybe down to something outwith your boundaries above , and the fact that after changing them they were no further breaks suggests that.

For example on another wheel I had a spoke break then the replacement broke , I looked at the hole in the hub the spoke was in and it was sharp like a knife where the spoke elbow rested against it , I rubbed down the sharp bit and replaced spoke for third time and been fine since .

 

[Yellow Saddle]

I appreciate your knowledge on the matter but when 3 spokes all trailing on NDS break over a 1000 miles then it is maybe down to something outwith your boundaries above , and the fact that after changing them they were no further breaks suggests that.

For example on another wheel I had a spoke break then the replacement broke , I looked at the hole in the hub the spoke was in and it was sharp like a knife where the spoke elbow rested against it , I rubbed down the sharp bit and replaced spoke for third time and been fine since .

Naming the spokes as trailing or leading doesn't help since a trailing spoke could be either outbound and inbound. It is only the latter that makes a material difference how the spokes are configured in the hub and the angle at which they're bent. Although a trailing and leading spoke undergoes cyclical stresses in different ways, this makes no difference. They both fatigue at the same rate. I'll explain. Let's assume the spokes on the left side are tensioned to 1000N. When pedaling, torque at the hub causes all the trailing spokes to increase tension and all the leading spokes decrease tension. It may help to visualize this by calling them pushing and pulling spokes. Even the strongest rider in a sprint produces only enough torque to increase/decrease that tension by 5%, in a wheel with 32 spokes. 5% up or down in a part of the spoke's strain graph that falls far short of the yield curve has no material effect on metal fatigue in steel. In other words, they all fatigue at the same rate.
Now back to your example. A poorly-built wheel will not have been stress-relieved and the base-line I mentioned in the previous post would not have been eliminated. Since one set of spokes are bent at the elbow more than the other set, the set with the more acute angle will fatigue faster. I'm sure this is what happened to your wheel but I can't say for sure because I don't know whether these were inbound or outbound spokes. Perhaps you can check and let us know.

As for the second example: sharp ridges in hubs where spokes exit are a big contributor to spoke fatigue. The use of soft aluminium hubs and stress relieving eliminates this problem in well-built wheels. I will be so bold as to say that your anecdote holds true for that wheel only and a general case can't be made.

 

[EasyPeez]

^This.

That paragraph is the same for me. running on R500s for about 8 months now, and still true.

Good news. No way they'll fit on my old chugger though. Can anyone recommend a cheap, hard-wearing MTB replacement wheel? I really can't see the sense in spending much given the low-quality of the bike generally and the fact that I'm skint buying kit for my new ride. How much is a wheel rebuild likely to be vs. a new wheel?

 

[Yellow Saddle]

Find a used wheel somewhere, even two will be cheaper than handbuilt. The latter is infinitely better but only of real use to high-milers and people who can't limp back home from a jungle expedition in Africa.

 

[EasyPeez]

Find a used wheel somewhere, even two will be cheaper than handbuilt. The latter is infinitely better but only of real use to high-milers and people who can't limp back home from a jungle expedition in Africa.

I'm confused...I thought you were telling me I should get the wheel rebuilt with new spokes originally?!

Have someone rebuild the wheel with new spokes and make sure they know how to stress-relieve the wheels.

 

[Yellow Saddle]

I'm confused...I thought you were telling me I should get the wheel rebuilt with new spokes originally?!

Yes I did say that but then you said the wheel is cheap and you don't want to spend money. It will be cheaper to buy a second hand wheel, especially since the new fad is 29" bikes and 26" ers are abandoned 'cause they're out of fashion. This will get you going quickly and cheaply and you won't have to doubt the builder's skill.