Wheels: Carbon Rims, Spoke Nipples

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832
Location
98245
After several years and several thousand miles, I finally popped a spoke on the Reynolds carbon wheels on my MTB. Actually, what happened was the spoke nipple head sheared off, freeing a spoke. The spoke itself was fine, no damage on the rim, so to repair it, I simply replaced the spoke nipple (I have a bunch of spare spokes & nipples from building wheels over the years) and re-sealed (tubeless) and retrued the wheel. In doing so, I noticed all the OEM spoke nipples are aluminum alloy. No wonder the head sheared off. Seems like a pointless exercise to save a few grams, on a MTB wheel that sees heavy duty and people run tires that weigh 600-900 grams!

I've always used brass spoke nipples on MTB and Tandems since they are stronger, they don't corrode, and they don't get bent out of shape when trued. I only use alloy nipples on road bikes where people really want to save a few grams. But since I haven't worked with carbon rims before, this had me wondering if there is a reason not to use brass spoke nipples on carbon rims. Or, maybe brass is better and I can expect more of those OEM alloy nipples to break?
 
Messages
2,407
Location
NY, NY
You need to use brass nipples on carbon rims. Alloy nipples react poorly to carbon. It’s an electrolysis thing. The tubeless sealant makes it worse.
 
Messages
2,407
Location
NY, NY
You know, brass is an alloy also.
Totally. I meant aluminum. Brass nipples don't disintegrate against carbon rims like aluminum ones do.
I did have a customer once that INSISTED I use aluminum nipples on his carbon rims. I used black ones that were powder coated instead of anodized. I never heard of any problems from him. Maybe they lasted just fine... Or he sold the bike.
 

MRC01

Thread starter
Messages
832
Location
98245
The wheel has 28 spokes; they are Reynolds AR Carbon wheels, 27.5" / 650, with straight-pull spokes. The spokes didn't feel super tight, tension seems about normal. I wonder if the spokes are long enough. When I unsealed the rim to replace the nipple, I noticed that in all the other nipples, the end of the spoke was not protruding or even flush with the nipple head, but they were recessed just a bit, like 1/2 mm. If the spokes were 1mm longer, they would pass through the nipple head which might strengthen it and prevent it from shearing off like this one did. If the spokes were a bit longer to protrude just a smidge from the nipple heads, there would still be a gap to the tape that seals the rim.
 
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