Originally Posted by
am8117
I might have used the term "preload" wrongly, and indeed they are not angular cup/cone bearings inside. I disassembled one in the past and all you find when you take off the nylon sleeve (labelled "do not disassemble" :grin
off ... are cartridge bearings. But cartridge bearings are not meant to have side loads on them and that would happen if the spindle was loosely fit. Of course from practical perspective this would cause chain rub, front shifting issues, etc.
Now to the overtightening ... try it. The spindle will move less freely. Some additional friction is added to the system and it cannot be the nylon inserts which are tight against the inner race of the bearing. I suspect it's the bearings having side loads applied as if the spindle trying to pull them both out of their races. That must affect bearings longevity if nothing else.
Yes, when I over tighten my cup and cone bearings in my wheel hubs the axle turns less freely. If it's over tightened, then it's not tightened correctly. Not sure where you are goin here.
Not all of the tightness you perceive is going to necessarily be bad for bearing wear though. Remember that these same grade bearings used in the BB are used in other things that handle many times more stresses at many times more speed and in much more adverse conditions.