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Broken spokes-me?

Old 07-18-12, 08:31 AM
  #1  
Rubato
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Broken spokes-me?

My wife bought a mid range bike while she was overseas, loved it, and shipped it home for daily use. I'm learning to build wheels and, of course, promptly squeezed the spokes. They seemed soft and I made a note to put her wheels on the stand and give them a bit of a tune up. When I did so, I found a broken spoke, on the rear, non-drive side. I changed it and then trued the wheel, which included retensioning to what I thought was proper. 3 weeks later, another spoke gave way. I'm of the belief that I need to follow the wheels I build in order to learn whether or not they are "good." I question whether or not my re-truing had anything to do with the 2nd spoke failure? If it was due to earlier fatigue while the wheel was too soft, should I expect more failures? Tensionometer is now at the top of the "buy" list....
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Old 07-18-12, 08:40 AM
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A good spoke would almost definitely not break after a couple of weeks. THe most likely scenario is that the spokes wer not properly tensioned and/or stress relieved when originally built (they seldom are) and the first few 100 miles on the bike fatigued the spokes to the point of failure. The fact you tried to re-tension the spokes soon before failure was just a coincidence.

The correct repair will be to cut out all the old spokes, put them in the metal recycling, and re-lace with new spokes (be sure to keep one drive-side and one non-drive-side spoke intact to ensure you get the right size). Bring the wheels up tot he proper tension, then stress relieve them, then re-tension them, then repeat until stress-relieving does not reduce the spoke tension. Check the tension on the wheels after a few hundred miles and re-tension one last time, if necessary.
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Old 07-18-12, 11:01 AM
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The wheel may have been built with a poor set of spokes and undertensioned. Get the tensiometer and see if that is the problem. You should shoot for 110kg on the drive side rear.
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Old 07-18-12, 11:21 AM
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Originally Posted by davidad View Post
The wheel may have been built with a poor set of spokes and undertensioned. Get the tensiometer and see if that is the problem. You should shoot for 110kg on the drive side rear.
It does not need to be bad spokes and undertensioned. Perfectly good spokes will not last long if severly undertensioned. And in my experience, undertensioned spokes are 100X more common than bad spokes.

Even crap-o-la spokes will have a reasonable life if properly tensioned and stress relieved.
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Old 07-18-12, 04:47 PM
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Originally Posted by DCB0 View Post
It does not need to be bad spokes and undertensioned. Perfectly good spokes will not last long if severly undertensioned. And in my experience, undertensioned spokes are 100X more common than bad spokes.

Even crap-o-la spokes will have a reasonable life if properly tensioned and stress relieved.
That's mostly true. I have a friend who bought a tourer with 36 spokes on the rear. He is not heavy and had not done any loaded touring when the spokes started breaking. We respoked the wheel with DT double butted spokes and he had no more trouble until the rim wore out.
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