Originally Posted by
Steel Charlie
I would be fascinated to learn what the exact recommended "preload" might and how one goes about measuring it. I hope that it's not the old BS about compressing a 10mm steel tube linearly with a quick release.
On Park Tool's website, they have a long and detailed article about cup and cone bearing adjustment. For this discussion, this is what matters:
The goal for adjustable bearings is to have the bearings rotate as freely as possible without any knocking or play.
The above indicates just taking out any slack, no tighter. This would definitely apply to road racers, where drag is everything.
For me, durability is everything. When I left the tiniest slack in my bearings, they wore, they spalled. Perhaps just adjusting out any slack would have prevented that. However, looking online for more knowledge, I ran across an article from a bearing manufacturer regarding proper preload, and I went with that as follows: To sense preload, you need to be able to spin the axle in your fingers, not wheel around fixed axle installed. There are various ways to replace the folk dropouts with spacers to check preload with QR closed. If, spinning axle in your fingers, it feels "notchy" (what Park Tool calls "binding"), the preload is too high. Even with no slack in the bearing, if it feels the same as that, in my experience, too loose, no preload. In between those two, is a setting where it doesn't feel notchy, but you can feel all the balls engaged when spinning; That's the sweet spot. On my current bike, getting this was extremely easy because I don't have QR axles. No axle spacers needed. The way it feels adjusted off the bike, is identical once installed. Adjusting to that sweet spot, on hub bearings, pedal bearings, BB spindles (cup and cone, not cartridge), drastically improved durability and eliminated need for readjustment, going on years and 10K+ miles now. Again, perhaps I would have had same result by only adjusting out all slack, but no axial preload. Don't know. I'll let you know if I find out.
EDIT!:
https://www.gmnbt.com/resources/guid...aring-preload/
Preloading a bearing helps prevent plastic deformation caused by overloaded bearings and optimizes bearing performance.
First, it’s important to know that a preload is required for angular contact bearings. This is because of the bearing design; it needs constant contact to happen between the balls and raceway. This constant contact is achieved through a bearing preload.
Radial ball bearings don’t need nonstop contact between the balls and raceway; therefore, a preload is usually not required.
Cone and cup bearings are angular contact.
QED.
Regarding the source of this discussion, external BB bearings, I don't know if mine are angular or radial contact.
More info (other website, and this time I'm bookmarking them all): "Excessive preload reduces durability. Lack of preload can cause "ball skidding". (I found evidence of ball skidding, linear spalls, in past rebuilds where I had small slack in hub and pedal bearings, no preload.)