Broken spoke AGAIN!

[redir]

Unbelievable! I've been one to break spokes. In fact I call my self the king of broken spokes. But this is the third one in as many weeks on 3 different wheels. I posted last week about my hub blowing apart, that was 3 spokes technically. The week before that I broke one on a 32 hole Durace/Open Pro wheel and then on this mornings commute, perfectly flat and smooth section of the bike path just cruising along and ping! Broken spoke on a 32 hole Ultegra Open Pro wheel.

I hope all bad things come in 3's. I just don't get it.

</rant>

[AngryScientist]

wow, that really is unusual. how old were those handbuilts?

[Mark McM]

Well technically, the Zipp wasn't broken spokes, it was a broken flange.

Contrary to common perception, spokes don't often break from a single, extreme overload, but instead they fatigue over time. (Sadly, fatigue is a poorly named phenomenon, which implies that the metal somehow gets weaker, until it is so weak that it breaks. In actuality, fatigue is caused by crack initiation and propagation. When final failure occurs, it is not because the metal is weaker, it is because the crack has grown so large that the un-cracked cross section of the metal is too small to bear the final load). The reason that sometimes spokes break when 'just riding along' is because they have fatigued (cracked) to a point where one final load cycle is enough to cause the final failure - and the spokes go through a load cycle on every revolution of the wheel.

So the question is, why did the spokes fatigue? Fatigue cracks can initiate due to manufacturing defects, stress concentrations, or locked in stresses (stressed locked into the cross-section when spokes are hardened, either through cold-working or heat treating), or a combination of all 3. Spoke manufacturer has gotten much better these days, so spoke breakage due to manufacturing defects is much lower than it used to be. Stress concentrations and locked-in stresses can occur due to wheel design and manufacture processes. Sadly, many wheel builders either don't know enough, or don't care enough about how to mitigate these factors.

Out of curiosity, where did the spokes break? The most common points are at the elbow, at the first thread, or at the head, so I'm guessing it was one of these. Would it be possible to get a sharp close-up shot of the failure? This can help determine what the cause of the failure was - fatigue cracks have certain tell tale features left behind on the fracture surfaces, so the point of crack initiation might be able to found. There are methods to mitigate the factors that contribute to spoke fatigue, so knowing the point of crack initiation might help determine what methods might be useful to prevent them from happening again.

[MattTuck]

spokes can smell fear.

[unterhausen]

I had trouble with some wheelsmith spokes because they can't form a head properly. Switched to DT after the second one broke. The heads popped off the Wheelsmiths, right at the transition. That's not where spokes usually break. Not building with them any more.

Coincidentally, the first one broke right as a truck backfired. Talk about jumping out of your skin.

[msl819]

Originally Posted by unterhausen

I had trouble with some wheelsmith spokes because they can't form a head properly. Switched to DT after the second one broke. The heads popped off the Wheelsmiths, right at the transition. That's not where spokes usually break. Not building with them any more.

Coincidentally, the first one broke right as a truck backfired. Talk about jumping out of your skin.

Someone was probably shooting at you!!!

https://m.youtube.com/watch?v=Tcwz8-EfFYE

[Lewis Moon]

front/rear - drive/NDS?

[unterhausen]

Originally Posted by msl819

Someone was probably shooting at you!!!

https://m.youtube.com/watch?v=Tcwz8-EfFYE

I almost thought that, bang-ping. But the backfire also had the typical turbine wind up beforehand. It crossed my mind that I might have gotten hit by liberated truck parts. Either way, it still made me jump

[berserk87]

Three words:

Too

Much

Power!!!!!!

[redir]

All were rear wheel. both on drive side. But I have broken non drive side too. I think the wheels are going on about ten years now. Fair amount of miles but not crazy.

I think I have some spare spokes that will fit it.

I think what it's trying to tell me is I need to go on a diet.

[AngryScientist]

Originally Posted by redir

All were rear wheel. both on drive side. But I have broken non drive side too. I think the wheels are going on about ten years now. Fair amount of miles but not crazy.

I think I have some spare spokes that will fit it.

I think what it's trying to tell me is I need to go on a diet.

if i were you....and i had wheels that were 10 years old with some miles on them and broken drive side spokes.....and i was frustrated at breaking those spokes....

i'd rebuild the wheels entirely, not replace individual spokes.

[redir]

Originally Posted by AngryScientist

if i were you....and i had wheels that were 10 years old with some miles on them and broken drive side spokes.....and i was frustrated at breaking those spokes....

i'd rebuild the wheels entirely, not replace individual spokes.

Yeah I know people say that and it's probably best but I'd rather just buy a new Open Pro wheelset. I have successfully built wheels in the past but am not too fond of doing it. So I would have to pay someone and at that point I may as well just go new all round. So in the mean time I just shove a spoke in there and carry on. These are 9/10 speed anyway so it's time to move on.

[unterhausen]

drive side spokes rarely break

[bikinchris]

Originally Posted by unterhausen

drive side spokes rarely break

Huh? Drive side spokes break just as often as non drive side. But pushing spokes break more often than pulling spokes.

[David Kirk]

Once you have a few spokes break you can bet that the rest will follow. I'd rebuild the wheel with fresh spokes and forget about it.

dave