Wheels: Carbon Rims, Spoke Nipples

[MRC01]

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?

 

[Taildragger]

I've broken spokes before breaking aluminum nipples with carbon Reserve 28H rims. Funny how things like that work.

 

[cjcride]

How many spokes on the wheel?
If low number, brass makes more sense.
My bet is the one that stripped was torqued too tight.

 

[NYEngineer]

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.

 

[UG_Passat]

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.

You know, brass is an alloy also.

 

[NYEngineer]

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]

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.

 

[MRC01]

Update: yet another nipple on the front wheel just popped. Just like before, head shears off and rattles around inside the rim as the spoke pops free. Anything can break once, twice suggests a trend. This Al-alloy spoke nipple on carbon wheels is definitely a "bad thing". The spoke is fine so it's not hard to fix, just a PITA with tubeless, removing the tire, sealed rim tape, then putting it all back together again. I replace them with brass, so I've got 2 done, 26 to go (when they eventually pop).

The first nipple popped after about 6 years from new. The second just 1 month later. So it appears to be some kind of decay that sets in incrementally over time.

 

[MRC01]

Just finished rebuilding the front wheel replacing all the spoke nipples with brass. As I was removing the alloy nipples, all of them were corroded, some a little, some a lot, and 4 of them were cracked / broken around the base of the head inside the rim which you can't see from visual inspection. So this wheel was going to fail, glad I got ahead of it. Should last forever now.

Lesson learned: alloy nipples with carbon wheels is a definite "no-no"! Reynolds and other manufacturers should not be building wheels this way. It's an example of the race to the lowest published weight at the cost of longevity. Lighter is not always better!

 

[y_p_w]

I tried building a front wheel (never been able to figure out how to dish a rear wheel) using aluminum nipples. I had to have extras because they were extremely easy to strip. If you've got a damaged one, just see if you can damage the threads easily with a utility knife. I'm not surprised that they would eventually pop out. I never actually rode on them though.

 

[MRC01]

Al-alloy vs. brass is all about the intended application. I've built many wheels with Al-alloy spoke nipples. As long as you have metal rims, and a good spoke wrench that fits properly, and it's for a single-rider road bike, it works fine and lasts indefinitely. For road bike wheels where you want it as light as possible, there's no real drawback.

For other kinds of wheels that have high stress, like MTB or tandems, brass nipples are the way to go. With carbon rims, there's a redox reaction between the Al and Carbon that causes the nipples to slowly corrode and eventually crack and fail.

Regarding dishing, it's all about the spoke lengths and tensions. For a given wheel that is already round & true, to shift the dish, change (increase or decrease, tighten or loosen) the spokes equally for all spokes on one side of the hub.

 

[y_p_w]

Al-alloy vs. brass is all about the intended application. I've built many wheels with Al-alloy spoke nipples. As long as you have metal rims, and a good spoke wrench that fits properly, and it's for a single-rider road bike, it works fine and lasts indefinitely. For road bike wheels where you want it as light as possible, there's no real drawback.

For other kinds of wheels that have high stress, like MTB or tandems, brass nipples are the way to go. With carbon rims, there's a redox reaction between the Al and Carbon that causes the nipples to slowly corrode and eventually crack and fail.

Regarding dishing, it's all about the spoke lengths and tensions. For a given wheel that is already round & true, to shift the dish, change (increase or decrease, tighten or loosen) the spokes equally for all spokes on one side of the hub.

My difficulty was in building a new wheel. When I needed to get one built to actually use, I just paid someone about $35 to build it, including the spokes and nipples. I tried one myself (kind of an experiment) and could never get the spoke lengths right and especially couldn't get it trued properly.

 

[MRC01]

Wheel building isn't hard. There are some good online guides to get started, like this and this. Anyone interested can learn, it just takes patience especially with your first wheel.
Truing wheels is quick & easy, that's a great place to start before you jump into building.

 

[y_p_w]

Wheel building isn't hard. There are some good online guides to get started, like this and this. Anyone interested can learn, it just takes patience especially with your first wheel.
Truing wheels is quick & easy, that's a great place to start before you jump into building.

I had a copy of The Bicycle Wheel by Jobst Brand. It was recommended to me by a really good bike mechanic. He actually said that my first wheel would probably be the best one I'd ever made because I would inevitably take a ton of time.

I remember that wheel, and I still have it somewhere even I don't ride any more. It was built from an old Record hub (the kind with a black grease hole cover that was part of a crashed wheel. I got it rather cheap as part of a clearance set - I think less than $100 for a full wheelset with Alpina rims. The hubs didn't have skewers, but I just used whatever I had. I then built it with a Mavic MA2 and DT spokes. I brought the wheel to a regular ride and asked some of the riders to evaluate my work. I was told it was done pretty well, but a little too tight for their tastes. It was easy for me because it was symmetric and I didn't have to deal with dishing.

Maybe it was around 2000, I got back into riding again and I got this Record hub from eBay. It was really nice, but it did have that really funky dust cap that needed a special tool to remove it without scratching up the aluminum. Well - I tried taking it off without it and now it's scratched. Funny you mention Sheldon Brown indirectly. I asked on one of the Usenet groups about that thing, and I think he answered that it was a real fiasco of form over function. This was the tool:

 

[MRC01]

The Campy super record that I had in the 1980s was very well designed & built. Extremely high quality, easy to service, disassemble and re-assemble. No special tools required, just the usual bicycle stuff. Friction shifting of course. The only things that wore out were tires, brake pads, chains, sprockets. Everything else was built to last forever.

 

[y_p_w]

The Campy super record that I had in the 1980s was very well designed & built. Extremely high quality, easy to service, disassemble and re-assemble. No special tools required, just the usual bicycle stuff. Friction shifting of course. The only things that wore out were tires, brake pads, chains, sprockets. Everything else was built to last forever.

What I had was mix and match. My first serious road bike was a 1988 Peugeot Bordeaux. It had a mix of everything, including French tubing, Maillard hubs, no-name rims, Shimano shifting, etc. But I had already swapped in those wheels I mentioned on it when my bike was totaled.

Those Record hubs weren’t necessarily the prettiest. I think this is it:

The hub I got on eBay was only on the market for a few years. I think this was it. Someone came up with that weird aluminum dust cap that snapped in.

 

[Surestick]

You can get a rear wheel dishing tool (and could make one yourself quite easily). It's just a flat piece of metal bent in a concave shape with a threaded bolt in the middle.
The ends of the metal piece touch the rim, the bolt touches the end of your axle, and the measurement should be the same on both sides.
Images of the tool.

 

[MRC01]

True, you can easily build your own dishing gauge.
Also, simply flip the wheel around in the bike frame, or a truing stand, and check that it aligns the same both ways.