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Broken spokes

I've never broken spokes before (well, once with a rear mech mishap, but that doesn't count).  That's no broken spokes for decades.  I now have some stupid-expensive carbon wheels and have had a spoke fail on the rear wheel - wheel out of true and a long walk home.  Turned out the spokes were too long and it was all rebuilt.  The front wheel turned out to be the same - overlong spokes, rebuilt with decent-weight spokes.  Now one of those new front spokes has gone.   It failed overnight -  It was fine after yesterday's ride - this morning it's sheared off at the end of the thread. Two failed spokes in six months.

They're the second pair of hand-built wheels i've had - the first pair are still true and survived a T-bone crash with a car at 20 mph without a scratch.  Have I been lucky for the past decades, or is something wrong?

If you're new please join in and if you have questions pop them below and the forum regulars will answer as best we can.

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hawkinspeter | 1 year ago

That sounds like poor wheel building to me.

It's slightly unusual for spokes to break at the thread end unless they're straight pull spokes as they more commonly break near the bend/hub. The first thing that springs to mind is that maybe they've used a slightly too short spoke. It really helps to have spokes the correct length so that you don't run out of thread when tightening them (i.e. too long) and that they have enough thread engaged to provide strength.

Carbon wheels shouldn't make much difference to the basic mechanics of how a wheel works, although disc brakes arguably (see other thread where I argued this) put more stress on the front wheel compared to rim brakes. I've snapped a front spoke on a disc brake carbon wheel whilst slowing for a red light(!), but that breakage was due to the nipple being corroded - the spoke itself was fine.

Spokes tend to be remarkably tough, so the most common mode of failure is when a spoke doesn't have enough tension in it. If it gets to the point where the spoke can become unloaded during a revolution, then it'll snap quite quickly as they're designed to be under continual tension. Over-tensioning spokes tends to cause rim issues (pretzel time), but I suppose that could cause a broken spoke too.

I did once have a cursed rear wheel (not carbon) that the bike shop used to replace the factory rear wheel (that broke). It snapped a spoke within about 10 miles of use, and after the shop had repaired the wheel about three or four times, I got fed up of leaving my bike with them, so I tried fixing the wheel myself and found that the rim was hopelessly warped. The only way I could get it to run true was by having unequal tensions in the spokes which doesn't make for a strong wheel (at that point I just bought a new wheel).

nniff replied to hawkinspeter | 1 year ago
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Thanks for your considered response - much appreciated.  I'm waiting for a call back from the bike shop, so we'll see.  My other wheels and the rebuilt back wheel were all done by the same LBS.  The rebuilt front and the original wheels with overlong spokes were done by a different outfit of generlly excellent reputation.  We shall see - I have ride London on Sunday - so it's quick repair or Frankenbike time

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