Originally Posted by
onespeedbiker
BTW, I have been riding bikes for 40 years and never had a left crank come loose (I simply torque them to spec), but I have heard anecdotal information that the left crank does tend to loosen more than the right. Have you ever wondered why the bicycle industry has addressed precession with rotating junctures such as the bottom bracket and pedals with reverse threading, but have completely ignored your discovery that it also occurs with non-rotating junctures, such as the crank arm attached to a square taper spindle? I understand how precession works with counter rotating junctures as the bearings that are rolling against the threaded cup of a BB or the spindle of pedal in a direction that will unscrew them, but how would it turn a bolt when there is no bearings counter rotating against it to unscrew it?
Hi,
Its not a "discovery" and I 've already outined my take on the subject.
If you can pick holes in what I actually said be my guest.
Don't try to say I said something that is clearly nonsense.
But I'll try again :
Unscrewing occurs from precession, in which a round object rolling in a circular ring in one direction will itself turn in the opposite direction.
For a pedal, a rotating load arises form downward pedaling force on a spindle rotating with its crank making the predominantly downward force effectively rotate about the pedal spindle. What may be less evident is that even tightly fitting parts have relative clearance due to their elasticity, metals not being rigid materials as is evident from steel springs. Under load, micro deformations, enough to cause motion, occur in such joints. This can be seen from wear marks where pedal spindles seat on crank faces ....
Precession forces are large enough that no manner of thread locking glues, short of welding, will arrest them ....
Jobst Brandt
If you don't care you have got the wrong end of stick as to where the
precession occurs and want to just insist I have that is up to you.
I'm happy that I know / understand what is going on.
And I worked it out without referencing JB at SB.com.
It has nothing to do with the bearings. It occurs between two threads.
rgds, sreten.