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Why spoke nipples break
In the last few months I have broken four nipples on the drive side of my rear wheel. Is it a bad idea to use aluminum nipples? I have had many wheels with aluminum nipples that I rode for years without problems. Or are there low-quality aluminum nipples out there that might have been used on my wheels?
Believe it or not, the fault probably does not lie with the nipples. You could have the best-quality aluminum nipples in the world, but if your spokes are too short on the drive side of your rear wheel, which I am willing to bet is the case with yours, your nipples will still break.
Another potential issue is if your rim has spoke holes without eyelets (so the edges of the hole sit right against the base of the head of the nipple) versus eyelets (either single or double) at each hole, which meets the base of the nipple head with a rounded surface.
I’ve asked wheel builder, college science professor, and passionate wheel researcher Bill Mould for a thorough description of the problem. Here is what he said:
“It’s interesting being associated with both the design and production end of the cycling business and also with the retail end. Because I work in a bike shop, I see things when they break, and a little analysis often reveals the cause. One very common failure in wheels is caused by incorrect spoke length.
The first example of this is spokes that are too short when used in conjunction with aluminum nipples. Figure 1 graphically shows this situation.
It is critical that the spoke extend all the way through the head of the nipple. If it does not, stress concentrations (a.k.a. “stress risers”) at the head of the nipple will cause it to break off. Customers come into the shop mistakenly thinking that they have instead broken a spoke (see Figures 2 and 3).
There are only two lasting solutions. One is to replace all the alloy nipples with brass ones that are not similarly vulnerable. The second is to replace all the spokes with longer ones and continue to use aluminum nipples. Both of these options are expensive and time consuming, and the causes were utterly preventable at no additional cost when the wheel was originally built.
Calculating the correct spoke length is a fundamental part of wheel building. Yet, in countless instances it is not done correctly, and trusting customers are stuck with the repair bill.
– Bill Mould / www.billmouldwheels.com
So there you go, Eric. Either replace those drive-side spokes and nipples, or at least replace the aluminum drive-side nipples with brass nipples.
Below is another letter I got from a reader with a similar problem that I had a back-and-forth email exchange with.
I’ve been having an issue with spoke nipples breaking on the PA-2 wheels that came with my Giant Propel road bike. I had two nipples break above the threads at the flange that sits on the rim bed. Both were the rear wheel on the non-drive side. The wheel is 24-spoke, radially laced on the non-drive side. While not specifically labeled as being tubeless ready, the rim profile certainly appears to be road tubeless ready when using tape (see image below).
I have been to two shops, the one where I purchased the bike and a local Giant branded shop. Both have told me that it was because I was running tubeless, but gave very different reasons.
The first shop suggested it was likely due to corrosion from the sealant. The second told me that it was not a tubeless compatible wheel and that the higher pressures of running a tubeless tire (I run 90-95psi) could cause rim/rim failure due to the sidewall not being as thick and different pressures on the rim.
The shop employee specifically cited the difference in rim profile between it and one of the full carbon officially tubeless ready SLR wheels. The only difference I saw was that one was carbon, the other aluminum. In 7-8 years using tubeless, I have never seen or heard of either of these issues being a problem.
As I have no way to contact Giant directly without going through the dealers, is it safe to assume based on the rim profile that at least the rim is tubeless ready and safe to run tubeless?
Giant confirmed that the P-A2 rim in Drew’s photo is tubeless compatible. However, Drew eventually discovered that the broken spoke nipples were due to the spokes being too short. He wrote back to me:
“I had the Giant dealer I purchased the bike from replace the nipples multiple times. The rear wheel was repeatedly breaking nipples and de-tensioning. I eventually broke down and completely rebuilt the wheels, same lacing pattern, with DT Swiss Aero Comp spokes in the rear, and Aerolite in front.
That was about six months and 4,000 miles ago. The only issue I’ve had was the rear going about 1mm out of true due to a broken derailleur hanger from a crash hitting a spoke.
I talked to a few other shops prior to rebuilding and we noticed that where the nipples were breaking the spokes were not threaded all the way in. They would break at the end of the spoke threads, right where the head started.
Both of the explanations offered by Drew’s shops are unnecessarily complex and don’t pass Occam’s razor, which states that the simplest explanation is most likely the correct one. While I have seen corrosion of aluminum rims from tubeless tire sealant with ammonia in it, blaming broken spoke nipples on it is a big stretch, since the quantity of sealant getting under the rim tape to the nipples will be zero or near that if the tire remains inflated.
And an explanation involving tubeless tires being run at higher pressures than tube-type tires doesn’t pass the smell test.
If the heads break off of spoke nipples, the first place to look is the length of the spokes.
Replacing spokes and not nipples
I am on a limited budget and wanted to know if it is possible to repair a tubular wheel with two-thirds of its spokes broken without removing the tire.
Last year, I purchased a set of Neuvation C50 carbon wheels for cyclocross. Three very kind engineering friends and myself (not an engineer) spent three nights in the garage gluing Challenge Grifo tires onto them. The wheels and tires worked really well until the last race of the season when I made the rookie mistake of putting my foot through my front wheel while trying to clip in at the start of the race. I broke about 8 of 20 spokes.
When I got home, I immediately de-tensioned the remaining spokes. The carbon rim appears to be true and all of the spoke nipples are exposed (none have disappeared into the deep rim). So, my question is whether there is a way for a mechanic to lace the wheel with the required new spokes without removing the tire so that I still have a good front wheel?
Or do I need to remove the tire and have the wheel properly rebuilt, if the rim is in good shape as I believe it is?
You definitely could not do it if the nipples are internal. But if the nipples extend below the rim, you can replace those spokes without removing the tire. It looks like those nipples are external, so you should be able to do it.
Lennard Zinn, our longtime technical writer, joined VeloNews in 1987. He is also a custom frame builder (www.zinncycles.com) and purveyor of non-custom huge bikes (bikeclydesdale.com), a former U.S. national team rider, co-author of “The Haywire Heart,” and author of many bicycle books including “Zinn and the Art of Road Bike Maintenance,” “DVD, as well as “Zinn and the Art of Triathlon Bikes” and “Zinn’s Cycling Primer: Maintenance Tips and Skill Building for Cyclists.”
He holds a bachelor’s in physics from Colorado College.