Originally Posted by
FBinNY
But that's not the point here, which is to clarify how headsets fail.
Your statements re impact and dimples imply a causal relationship. That would be true IF the dimples were caused by impacts (brinelling). However, the dimples we see in worn headsets are not impact related at all, They're caused by vibration and lubrication failure. The correct term for this is fretting, aka false brinelling, and there's plenty of literature on this subject. (search fretting bearing failure) Headsets fail because there's inadequate movement, so lubrication at the contact points doesn't get replaced and vibration causes abrasion at the dry ball/race interface.
If one is truly focused on headset life, one might bet far and away the most bang for the buck by using any decent quality headset and lubrication with a grease known for it's anti-fretting properties.
Having had to replace many headset in mountain bikes during the rigid/threaded headset era, I can tell you that the failure that I am describing
is not a lubrication failure nor strictly due to vibration. The failure could happen in a single ride with a new headset. Up to the point where threadless headsets became ubiquitous, headset loosening was a major problem, especially in mountain biking. There was a large cottage industry during that era of making locking mechanisms to keep the threaded headset tight. Unfortunately the locking mechanisms had only limited success. A loose headset in a situation where there is serious stress on the headset that ended with
true brinelling where the damage is plastic vs corrosive. Yes, the headset is vibrating but the impacts were causing the brinelling.
This kind of damage almost completely disappeared with the introduction of the threadless headset that didn’t loosen due to vibration of the entire headset/fork system. Denting of headsets on mountain bikes can still occur but it is rare and I would certainly agree that, in that system, it is false brinelling.