Saturday, April 12, 2014

Nipple Alert

The tune up was going smoothly. Too smoothly. The owner of the bike is a big guy who rides a lot. How was I breezing through this toward my fast-approaching deadline? I'll just pop these wheels in the truing stand, even though they look pretty good.

I'd noted that whoever built the wheels had used alloy nipples. Don't get me started on alloy nipples. I've seen a lot of them sheared off over the years. But I began to wonder if alloy nipples might be the safety valve to take some of the strain off of heat-treated rims that fatigue and crack.

In the stand, the rear wheel looked pretty straight, but I saw a tiny waver I could reduce to nothing. I set the spoke wrench on the flats of the nipple and barely shifted my fingers. The nipple crumbled to powder. It took no force at all.

On an older wheel I check for cracks in the rims. On eyeleted rims I look for loose eyelets. So when I surveyed the wheels for more deterioration I marked bad nipples with red tape on the spoke and bad eyelets with a bit of tape on the rim.
I can't say for sure how close the wheels were to catastrophic failure, since the spokes still held even after the nipples had crumbled under exploratory pressure, but they weren't being ridden over rough roads by a large guy right then, either.

Particularly disturbing was the number of bad nipples in the front wheel. If eight spokes decided to let go at the same time in a front wheel I think you'd stop pretty abruptly. And that's in a conventional wheel with 36 spokes. Do the math. Reduce the number of spokes, correspondingly increasing the load on each one and then subtract a bunch all at once. A rider I know lost ONE spoke in a Mavic wheel on a fast descent and it almost locked up the wheel completely. He was able to bring the bike to a controlled stop, but it was a scary few seconds.

So, my weight-conscious friends, examine your wheels very critically if you have had them a few years. These wheels had a lot of miles, so fatigue is not unreasonable, but if no one had checked they might have announced their retirement at a surprise party they threw for themselves.


Steve A said...

Don't recall aluminum nipples on any of my wheels, but a few of same have never been adjusted for trueness due to nonstandard rim/nipple combinations.

cafiend said...

Are the nips just different sizes? I mean, there's a spoke wrench for every size and type. Truing might just be more cumbersome.

I'm big on the quest for truth.

Steve A said...

Mavic Ksyrium wheels are odd. Same for some Rovals (Specialized).

cafiend said...

Way too much weird in the world of wheels.