If I had a nickel for every time I said that upper headset bearings never wear out, I’d have… a few bucks anyway. Upper headset bearings usually do last a very long time. Lower headset bearings take all the pounding, and they are located in the second dirtiest area of a bike, at the top of the fork where the front wheel sprays up road grime.
The dirtiest area is at the back of the bottom bracket. (Hey, let’s mount the rear brake there!) But this is a story of headset bearings, not bottom brackets and brakes.
A friend showed up in the garage recently with his tri-bike. It had serious problems, not least of which was a rear bar-end shifter that went slack in the middle of a full Ironman, requiring him to ride the remainder of a hilly bike leg on the 11 cog. And also not least was a completely seized rear brake mounted guess where? But this is a story of headset bearings, not shifters and brakes, so on to headset bearings.
The most serious problem was a fork steerer tube that had been sawn partially through by a seized headset bearing. The bearing had been replaced, but the damage was done. I knew something was wrong when I could not dial in a proper headset adjustment. When I took it apart, I was quite alarmed.
Normally the inner race of a headset bearing is static with respect to the fork and rotates with respect to the outer race, of course. But if the bearings becomes seized, the fork rotates back and forth inside the inner race (or the entire bearing rotates inside the bearing cup; I guess forks are cheaper than frames.) Anyway, in an abrasion war, hardened steel wins every time against a carbon fiber/resin composite.
I don’t know how long the upper bearing was seized, but it couldn’t have been much fun driving the bike in this condition. Maybe this is why he was erratic. I thought it was just because he was a triathlete. I’m sorry. That was a mean joke. The guy rides very well and is an accomplished road cyclist.
But upper headset bearings last forever. So what went wrong? In a typical road cycling position, the rider’s chin is behind the headset. However, in an aggressive triathlon/time trial position, the rider’s chin is well in front of the headset. I think this leads to sweat dripping into the bearings. The rusted stem bolts were a clue. It occurs to me that a bike used on a stationary trainer might also be prone to this issue.
Here are some ideas/suggestions on this topic:
- Threadless headsets are easy to service. So a regular inspection is a good idea. While you’re at it, clean up the steerer tube and check it for cracks or other defects. Here’s a Global Cycling Network video on headset maintenance.
- Pro tips for headset work:
- Unbolt the front brake from the fork (usually a 5mm allen screw in the back of the fork) and just let the brake dangle, so you don’t have to disconnect the brake cable to lift the stem off of the steerer tube.
- Mount the bike in your workstand with the front end down so that the bars/stem can hang from the cables without kinking.
- A bit of steerer tube deformation under the upper bearing compression ring is not unusual, but nothing like the material removal in the picture above. If the deformation prevents proper bearing adjustment, it’s time for a new fork. I have an old fork hanging in the garage with exactly this problem.
- If you can’t properly adjust a headset, it might be a simpler problem of not enough spacers. The total height of your stem and spacer stack must exceed the height of your steerer tube by enough (3-4mm?) so that when you tighten the stem cap, it pushes down on the stack. If the steerer tube height is near or equal to the height of your stack, the cap will just tighten down against the steerer tube.
- Don’t use carbon assembly paste on the steerer tube. If it gets between the bearing and the steerer it makes excellent grinding compound. There is plenty of clamping force between the stem and the steerer tube. Besides, in a crash, would you rather have your bars rotate or snap off the steerer tube?
- Do I have to tell you to follow manufacturer’s torque recommendations (usually 5nm) for stem bolts?
- Some fork and frame manufacturers have specific guidelines about spacers (maximum/minimum number and location) and internal compression supports to prevent crushing the steerer tube with the stem.
Bonus picture: Here is a steerer tube that was about to fail! What looks like a hacksaw cut is actually a crack. The rider felt his handlebars getting a little “soft” and finished his commute “gingerly”.
I’m not sure this failure had anything to do with headset bearings. It is just sort of interesting in a scary kind of way.
That’s all for now. Thanks for reading!