Spokes breaking above nipple

[tellyho]

Seeking thoughts. This is on my full-suspension, 145# rider, 28 spoke wheels 3x, Bitex to DT Swiss, db Pillar spokes. Replaced two spokes so far after they broke just above the nipple. Tension is appropriate. Was cleaning the rim to retape after replacing the most recent spoke and dropped the wheel 3 feet onto concrete - another broken spoke. Needless to say, I'm rebuilding the wheel with new spokes and nipples but any thoughts as to causes? I've never had remotely this much trouble with any wheel I've built. It's probably 5ish years old and has not seen a ton of miles.

[bikinchris]

It's always possible that you have a bad set of spokes and rebuilding the wheel will be a final solution. However, I think for most people 28 spokes on very rough terrain is too few.
Spokes break because they can't carry the load and they become un-tensioned during use. The working metal going from tight to loose and back cold works he metal until it becomes brittle. Having fewer spokes means each section of the rim carries more of the load. Therefore, you can experience spokes going slack on the bottom of the wheel. Disc brakes make it worse. Under heavy braking spokes can go slack with the hub twisting in relation to the rim. Grab the brakes hard and often enough and you have cold worked the spokes.
In other words, wheels actually stand on the bottom spoke, not hang from the top spoke. That's why tandems used 48 spoke wheels crossed 5 times from the flange to the rim. They each lean on the crossed spokes and involve more than just the one spoke on the bottom.

[rowebr]

Originally Posted by tellyho

Seeking thoughts. This is on my full-suspension, 145# rider, 28 spoke wheels 3x, Bitex to DT Swiss, db Pillar spokes. Replaced two spokes so far after they broke just above the nipple. Tension is appropriate. Was cleaning the rim to retape after replacing the most recent spoke and dropped the wheel 3 feet onto concrete - another broken spoke. Needless to say, I'm rebuilding the wheel with new spokes and nipples but any thoughts as to causes? I've never had remotely this much trouble with any wheel I've built. It's probably 5ish years old and has not seen a ton of miles.

I'm not sure where the breaking point was for you: Is the spoke breaking off within the nipple? Or is the nipple and threaded portion of the spoke intact after the break?

If breaking within the nipple, maybe your spokes are a bit too short on this wheel. Can you see the threaded end of the spokes coming up flush or just past the head of the nipples?

[tellyho]

Originally Posted by rowebr

I'm not sure where the breaking point was for you: Is the spoke breaking off within the nipple? Or is the nipple and threaded portion of the spoke intact after the break?

Break is right above the top of the nipple for all of the spokes that have broken.

As for # of spokes, 28 is the standard on mtb wheels at this point. I'm just riding XC, no big drops or anything crazy.

[rowebr]

Originally Posted by tellyho

Break is right above the top of the nipple for all of the spokes that have broken.

As for # of spokes, 28 is the standard on mtb wheels at this point. I'm just riding XC, no big drops or anything crazy.

Got it. Then my guess is that the spokes are a little too short, they don’t extend up to the head of the nipple. Roger Musson’s book explains this can lead to spoke failures.

[djg21]

Originally Posted by rowebr

Got it. Then my guess is that the spokes are a little too short, they don’t extend up to the head of the nipple. Roger Musson’s book explains this can lead to spoke failures.

When I’ve seen this happen, the wheel build has been an issue one way or another, and the spokes weren’t tensioned correctly. I’d rebuild the wheels or have them rebuilt with new spokes and nipples, assuming that the rims are still round and true.

[DfCas]

Be sure to use butted spokes on your rebuild.

[November Dave]

You might have a directionally drilled rim with the spokes laced against this pattern. Normally spokes that are tension cycling break at the hub but that’s probably the best guess as to what’s happening here.

Depending on rims (mostly), a 28h build can handle a gorilla. My guess is a build issue, not a materials issue.

[Mark McM]

Originally Posted by November Dave

You might have a directionally drilled rim with the spokes laced against this pattern. Normally spokes that are tension cycling break at the hub but that’s probably the best guess as to what’s happening here.

I would also guess that this may be a possibility.

When you say the spokes break, "just above the top of the nipple,", I think there may be a nomenclature discrepancy. Usually, the head of the nipple is considered the top of the nipple, but I guess you mean the break is below the shaft of the nipple. Presumably, the spokes are breaking at a thread (the weakest part of a spoke). If the threads are showing below the nipple shaft, then the spokes are likely too short, which could be a contributing factor to their breakage.

[tellyho]

Yes, I'm wondering if I laced in the wrong direction. I'll keep an eye out as I pull the wheel apart and see if I can figure that out. It seemed non-directional when I built but that was a while ago.

[slambers3]

You have a pool? Or near the ocean? A lot of weird spoke breakage from storage near pool chemicals or salty air

[Flinch]

Originally Posted by Mark McM

I would also guess that this may be a possibility.

When you say the spokes break, "just above the top of the nipple,", I think there may be a nomenclature discrepancy. Usually, the head of the nipple is considered the top of the nipple, but I guess you mean the break is below the shaft of the nipple. Presumably, the spokes are breaking at a thread (the weakest part of a spoke). If the threads are showing below the nipple shaft, then the spokes are likely too short, which could be a contributing factor to their breakage.

^
This. I had same problem on a factory wheel and it was too short of spokes. Check to see if the spoke end pokes out at least flush with the head of the nipple, or if it is 'sunken' . If the latter, then bingo!

[tellyho]

Looked again at the wheel today and I do think I put the rim on backwards (as in, spokes in holes leading the wrong direction). This would be an easy explanation for my problem as well as an easy fix. Also embarassing

[oldpotatoe]

Originally Posted by November Dave

You might have a directionally drilled rim with the spokes laced against this pattern. Normally spokes that are tension cycling break at the hub but that’s probably the best guess as to what’s happening here.

Depending on rims (mostly), a 28h build can handle a gorilla. My guess is a build issue, not a materials issue.

That's the first thing that came to mind for me too. The nipples/spokes aren't leaving the rim at the proper angle because of the orientation of the holes in the rim..in other words, the rim is built 'backwards'...

Are the holes on both sides of the rim drilled on the centerline of the rim or offset?..On the rim strip side if the hole is offset to the right, the spoke should radiate to the left flange..since the holes are drilled outside in.