Spacers with a flat surface on the inner diameter can help prevent your headset from loosening. Just to clarify: If your headset stays put as it is, then don’t change it! It’s just that my headsets kept loosening on two different bikes, and so I was looking for a solution.
Classic headsets use a locknut at the top to maintain the headset’s adjustment. It’s essential to prevent the upper headset cup and locknut from turning together, as this would loosen the headset. A keyed washer between the top cup and nut stops that rotation – in theory. In practice, this system does not always work: The keyed washer tends to turn anyhow, because the key is too small. And you cannot make it bigger without weakening the steerer tube.
When the washer is made from steel, it can mess up your steerer tube’s threads if it turns (very bad). With an aluminum washer, the steerer tube simply cuts new threads as the washer turns (not good). In both cases, the key is not sufficient to stop the washer from rotating.
The solution is simple: Use a flat surface on the steerer tube, and a matching flat surface on the spacer, to provide more material area than a narrow key. French bikes (and some British ones) used that system, and it worked better. The headset cup doesn’t turn with enough force to cut threads into all that aluminum.
Compass made the spacer taller than a simple washer, which provides even more material to resist the turning torque. And since the spacer is so effective in preventing the system from rotating, it’s not necessary to tighten the headset locknut with force. A little more than finger-tight is sufficient to keep it from loosening. You can use a single headset wrench: Tighten the top headset cup first, insert the spacer, then (lightly) tighten the locknut. Don’t overtighten the locknut, otherwise, the spacer can jam.
It’s easy to retrofit your bike with this system: Machine or file a flat on the back of the steerer tube that matches the inside of the spacer. This doesn’t weaken the fork: You only remove the raised portion of the thread, which didn’t add any strength to the steerer.
I’ve used prototypes of these spacers on my Mule for thousands of miles and dozens of Rinko disassemblies. They have performed great, and they’ve solved the loosening of the headset on this bike.
We now offer the spacers in 5 mm and 10 mm thickness. If you need an in-between thickness, just add standard headset washers (without tabs) to make up the difference. Or cut a few millimeters off your steerer tube to match the spacer, as I did on my Mule.
Click here for more information or to order these spacers. As I said before, if your headset works fine, don’t change it. But if it keeps coming loose, this may be the solution.