[quote=buck91]...
Some bicycle bearings are likely more highly stressed than automotive wheel bearings, considering how short-lived they are even if well lubricated.
Now, I haven't had the chance to put tens of thousands of miles on any set of bearings; end up upgrading or whatever sooner. But my experience has shown the bearing failures are typically due to poorly adjusted preload (either too tight or too loose). ... Seems somewhere like 100% of the wheels I've found coming from various suppliers had grossly over tightened bearing preload. Even many brand new hubs, though I have found that the nicer units tend to be more appropriately set up from the factory.