Busted spoke on light weight front wheel...questions

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peligro
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Joined: Sun Apr 21, 2013 4:09 pm

by peligro

I built a front wheel with a BHS light weight front hub, a Kinlin XR200 rim, and 24 sapim laser spokes, laced radially, elbows in.

I have I'd guess between 3 and 5k miles on this wheel and just busted a spoke, which made for an unpleasant ride home since the wheel went very far out of true.

The wheel was built with a tension meter and the tension was not perfect but within 15kgf either way of 110kgf. I weigh 160lb and am riding on mixed roads.

I replaced the spoke and retrued the wheel but its got me a bit concerned that it will happen again. The rim was not perfect to begin with and the tension is about as even as I can get it while maintaining trueness. You guys think I'm going to continue busting spokes?

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TrekUk
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by TrekUk

lightweight = reduced strenght, even if built well the wheels will never be bombproof.
Madone Five Series 2013
Shimano Dura-Ace 9000
Mavic Cosmic SLE 2013

by Weenie


Orfitinho
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by Orfitinho

Where did the spoke break (near elbow, near nipple)? Can you take a photo?

bobqzzi
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by bobqzzi

If it broke at the thread or mid span, it was a defective spoke. If it broke at the elbow, did you stress relieve it when you built it?

peligro
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Joined: Sun Apr 21, 2013 4:09 pm

by peligro

bobqzzi wrote:If it broke at the thread or mid span, it was a defective spoke. If it broke at the elbow, did you stress relieve it when you built it?


It broke at the elbow, yes, I stress relieved by grabbing spokes when I built it.

For a lightweight wheel like this, what's the max variation in spoke tension you'd accept?

bobqzzi
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by bobqzzi

10% or so maybe a little more for the ones at the joint. Are you saying that this one was from 95 to 125? That's quite a bit.

bm0p700f
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by bm0p700f

Yes your tesnion variation is too high. 15 kgf is about 150N that is way too much more than 10%. I build with these rims and no more than 5% variation in tension is possible around the average. That will improve spoke life alot as I bet it was a low tension spoke that broke. Unfortunatley you did a poor build. Rebuild with new spokes and work on getting more even tension. max (often less) 5% variation and no more than 0.3mm rondness variation is what I look for when building with this rim. Even tesnion is more important than how round the wheel is anyway.

It is easy to get a wheel with 0.1 mm lateral trueness
Last edited by bm0p700f on Mon Apr 22, 2013 9:14 am, edited 1 time in total.

mentok
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by mentok

+/- 15 with lasers is a big range. with a park tm-1 that's like having spokes spread across 3 or 4 readings which is a pretty big difference.

i second the notion to re-build. 24x lasers will only cost you ~$30 and a bit of your time to improve your building skills and also make a more reliable wheel.

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WMW
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by WMW

peligro wrote:It broke at the elbow, yes, I stress relieved by grabbing spokes when I built it.


Grabbing spokes isn't enough IMO. Did the wheel stay true from the start?

You said 110+-15kg... way too much variation. Try 95+-5kg. Shoot for .010" radial variance and .005" lateral. I've built a lot of them. Front wheels just don't need a lot of tension, and you should not need that much variance unless the rim is bent. Even tension is more important than getting it perfectly true. And mark the spokes for windup.

And take a spoke wrench with you... my multi tool has one. I can't remember the last time I broke a spoke, but I've fixed other people's wheels...

BTW... I have >10k miles on a set of XR200s with 20f @170 lbs and no issues until I slammed into a pothole and dented the rim...
formerly rruff...

peligro
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by peligro

Thanks for the replies, appreciate the advice.

eric
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by eric

I had some break like that on my UL hub.

Try lacing heads in.

The BHS UL hub has large chamfers on the outside of the spoke holes. When you lace heads out the spoke head fits in the countersink. That leaves the elbows unsupported. According to Jobst's book that causes breakage, and the right way to use a countersink is to put the elbow in it. With these hubs that means heads in.

I've switched to building mine that way. Some radial, some 1x.

by Weenie


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