Roval Control Carbon Wheels - Spokes breaking...alot

[shirk]

To be fair, the rims have been great and when getting repaired we were using double butted spokes as nobody stocks the proper CXRays around here.

Orange is a distributor for Sapim, they are here in N.Van and have stock. After the first quick repair your shop should have ordered you proper CX-Ray spoke then replace when arrived.

Willing to bet the initial build was off if you've now had a couple months of riding without spoke blow outs.

[robnow]

Ok, so pretty much one month exactly that I've been on this rebuilt Nox wheel set and I'm busting spokes again, 2 in the last 3 rides. Just like before the spokes breaking are on the rear non-drive side.

Just to re-iterate:
- Nox Composites AM 275 rims on I9 hubs with Sapim CX-Rays, 32 hole
- after 1 month riding, busted 8 spokes within 2 weeks (1/ride), ALL rear non-drive side b/w nipple and spoke taper
- Nox took them back to rebuild
- 1 month back on them and now same thing happening
- My shop guys with plenty of wheel building experience suspect its the angle of which spokes come out of rim on that side, Nox says its normal, I should take a pic tomorrow to post up
- Second theory suggests spoke prep(almost like a loctite) being used may be weakening threads???
- Spoke tension is balanced

I've emailed Nox to notify him but what should I expect?

Worst comes to worse seems like I may have to rebuild with different spokes and take a drill bit and by hand add an angle to the spoke holes.

[jono]

Pics sound useful. If you've got the broken spokes I'd be interested to see close-ups of the breaks; you can often see where the crack started that way, and if they're consistent you might have your answer. Understanding these are all non-drive side, are they also breaking on the inside or outside of the flange, or both sides?

[robnow]

Don't have any of the broken spokes. Not sure whether most have broken at the first thread or at the exit of the nipple. I'm pretty sure some have broken even a little further up but not at the taper or flat. BTW, no spoke prep being used. The last two spokes replaced are both on OUTSIDE of flange.

I believe they are trying to be helpful but at this point them and my shop peeps are perplexed. Nox swears the hole/nipple angle has nothing to do with it and that I'm the only person to report spokes breaking in this manner. Interestingly the next generation rims coming out this month will have angled spoke holes. Otherwise rims have been absolutely bomber.

[jono]

I would think they've had this discussion with your shop guys, but just in case: do they spec spoke tension? With high tension bending stress at the nipple can more reasonably be ignored; at low tension the bending stress is a larger fraction of the total. This is in addition to the fact that low tension fatigues your spokes faster by itself, so I'd check into making sure they are building close to the max allowable. Everything else you've described sounds consistent with fatigue failure so far.

[robnow]

Thanks for the feedback jono.

2 more broken spokes yesterday, the same, rear non-drive side outside flange. Had a close look at both and they broke at first thread.
Hard to show the angle in a pic but I'm still convinced the nipples aren't coming out at the proper angle. You might be able to see how the spoke isn't centred in nipple and resting on the edge of one side.

They are building wheels at 120 kgf +/-10%. They also said this second rebuild was built stiffer than the original.

[jono]

That angle doesn't look too crazy to me on its own, but obviously it's not helping. And the spokes on the outside of the flange would suffer the most, of course. If you're down to minor experimenting either get the new rim or, for a wild goosechase, try putting a wide radius bend into the round part right between the threads and the taper. Not a super wide radius, maybe like 5-10 mm, and bent over something soft like a finger on the inside but pressing against something firmer on the outside so you don't accidentally bend the threads or even near the taper. This should be similar to the angle adjustment that happens at the hub, so the shop guys would probably be familiar with the idea. You'd want them all bent at the same angle (preferably once) and then built up. Might help, since the angle is small. But the new rim sounds better.

A rim with angled spoke holes should seat the nipples better, too, and with the gap on one side like that it's possible that the nipple is actually seated badly enough to rock a little. On a left turn with more weight leaning inside, say. If so that changes the stress in the spoke dramatically each time, and would be another path to quick fatigue. You might be able to watch for that by holding the hub and putting a side load on the rim, but it would probably be too slight to notice unless you can hear it or something.