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Broken spokes - wheel/hub/what?

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Broken spokes - wheel/hub/what?

Old 10-18-06, 08:50 AM
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jimmuter
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Broken spokes - wheel/hub/what?

I've had my bike for almost 10 years. A little over a year ago, I started breaking spokes on my rear wheel every once in a while. I decided to have the wheel replaced by my LBS. A month ago, I broke a spoke on that wheel. It broke off right at the hub. I had it replaced and broke another one a week later, again, right at the hub. I had that fixed and broke another a few days later, you guessed it, at the hub. On the bright side, I now know how to replace a drive side spoke on my rear wheel. I had a knowledgeable friend look at my wheel and he says it's a quality wheel. I haven't gained a bunch of weight -- in fact I've lost some.

My questions: Should I just rebuild or replace the wheel being that it's likely spokes will keep breaking? Could it be some issue with the hub because that's where they keep breaking? What is the useful life of a wheel? My bike is a Trek 720 hybrid -- nothing special, but I ride it a lot and it's been dependable.
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Old 10-18-06, 09:12 AM
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Sounds like a case of low-quality spokes, probably compounded by low-quality wheelbuilding (by a robot). If it were me, I'd have a brand-new wheel built by hand by a good wheelbuilder, using DT or Wheelsmith spokes.
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Old 10-18-06, 10:53 AM
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Usually when spokes break at the hub it's a sign of insufficient spoke tension. Loose spokes flex more and the continuous flexing fatigues the metal in the "J" bend at the hub. But this happens more often on the non-driveside where tension is lower due to asymetrical wheel dish.
In your case mechBgon may be exactly right, poor quality spokes.

Al
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Old 10-18-06, 12:47 PM
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Originally Posted by Al1943
Usually when spokes break at the hub it's a sign of insufficient spoke tension. Loose spokes flex more and the continuous flexing fatigues the metal in the "J" bend at the hub. But this happens more often on the non-driveside where tension is lower due to asymetrical wheel dish.
In your case mechBgon may be exactly right, poor quality spokes.

Al
I agree for the most part but would add that this is a 10 year old wheel. What you have, Jimmuter, is a classic cascade failure. One spoke breaks and the stress is spread around to the other spokes. They are as old and tired as the broken spoke so the extra stess does them no good. You put in a new spoke and tighten it up but maybe don't get back to the same tension. The old spokes around it now start to fail. New spokes, old failures, new spokes...pretty soon you are chasing spokes all around the wheel, the wheel is poorly tensioned and even the new spokes start to fail.

It's time. New spokes, probably a new rim and maybe time to splurge on those Phils you've been lusting for You know you want them. Doncha? Huh? Nice and shiny.
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Old 10-18-06, 12:53 PM
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Originally Posted by cyccommute
I agree for the most part but would add that this is a 10 year old wheel.
Actually, the bike is 10 years old. The wheel in question is just over 1 year old. The wheel I replaced last year lasted 9 years.
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Old 10-18-06, 01:35 PM
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Originally Posted by jimmuter
Actually, the bike is 10 years old. The wheel in question is just over 1 year old. The wheel I replaced last year lasted 9 years.
Reading comprehension isn't my best assest sometimes My explaination still applies, however. The wheels were probably poorly built or not stress relieved properly. The wheel will stress relieve on its own (the spoke head will bend to conform with the hub) but that leads to detentioning of the spokes. Relacing and retentioning should solve the problem.
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Old 10-19-06, 02:08 AM
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Originally Posted by jimmuter
Actually, the bike is 10 years old. The wheel in question is just over 1 year old. The wheel I replaced last year lasted 9 years.
I would fix the brken spoke, retension the wheel and then see how you go. I had this problem 3 years ago, broke two spokes one after the other. Fixed them and 14k km later I have had no problems whatsoever.

Hub problems are hub problems, spoke problems are spoke problems, rim problems are rim problems. If your hub were shot for example, spokes could still be ok.

Good luck.
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Old 10-19-06, 10:30 AM
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Maybe the spoke holes in your hub are a bit oversized, which would compound the problem of having low-tensioned spokes. Perhaps rebuilding the wheel, or just the drive-side, with quality spokes and spoke washers at the hub would solve your problems.
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Old 10-19-06, 10:46 AM
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Take the wheel to the shop and have them put a tensiometer on the spokes. The tension is probably too low - if the tension is OK (105 kg or more) you should get better spokes. Maybe butted 2.0/1.8/2.0 mm - the thinner middle section allows them to stretch more under shock loading.
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