Bicycle Mechanics - Broken spoke
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07-23-08, 08:04 AM
My Dahon folder has suffered a broken spoke on the rear wheel twice in the last 3 weeks and now I'm getting a bit worried. I've taken the bike to my LBS to replace the spoke and re-balance the wheel, but I'm concerned that spokes are breaking because of the weight on the bike - I weigh 115kg + the weight of my backpack (~2.5kg).
This might seem like a daft question, but what generally causes broken spokes and what can I do to avoid them or at least significantly lessen their occurrence in future? Don't say "lose weight" as I'm 2m tall and not very overweight ;)
07-23-08, 09:10 AM
You did not tell us where the spoke broke. If it broke at the elbow, then the normal reason is "too loose". The low spoke tension allows the strain on the elbow to work back and forth untill metal fatigue in that part of the spoke causes failure. This is compounded by heavy loads and on a normal wheel, the lower spoke tension on the non drive side of the rear wheel. (I have no experience with the wheels on a Dahon folder). At your weight, it might be to your benefit to speak to a custom wheel builder to see if a handbuilt wheel set is in your future.
Once your wheel starts to break spokes like this, its only a matter of time till the others break also.
07-24-08, 07:47 AM
Thanks for the reply, very informative. The spoke broke on the elbow on the drive side so I guess that would've hastened the breaking. I guess I need to instruct my LBS to ensure that none of the spokes are loose.
My weight is about 100 kg as well. I never broke a spoke in more than 30 years. A well made wheel is remarkably strong, much stronger than most people think; able to carry up to 700 (!) times its own weight.
Spoke tension should be equal and high, making the wheel "inert", not vurnerable to metal fatique.
It is not a good idea to simply replace one broken spoke. Have all spokes replaced and the wheel rebuilt from scratch by someone who knows what he's doing.
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