Originally Posted by
jimmuller
If friction from the spindle transmitted to the cup through the bearings was the reason for the cup moving it would tighten a right-handed thread on the right side of the bike. It doesn't do that.
It's not friction. It's thrust. There is a difference which you are confusing. In this case, the difference causes the cup to turn in the observed direction which is opposite to the direction it would turn if it
was friction.