[Shotimes] Re: Shotimes digest, Vol 1 #5001 - 3 msgs

[MonsieurBoo@aol.com]

>> I believe "ground zero" is +42mm offset, regardless of rim  width.  Thus 
getting wider rims shouldn't make a difference on the stress,  as long as the 
offset is the same.

>> On the other hand, I would  think that any time you move the wheels out 
(or in for that matter) you change  the stress on the bearing, cause you are in 
effect changing the relative pivot  point when you insert spacer, or when you 
install wheels with a different  offset.

 
 
I agree more with the "other hand".   There are a couple things  to consider, 
(a) equalizing the weight distribution and (b) not increasing the  "moment 
arm" excessively.
 
The amount of positive or negative offset affects both.  Naturally  one of 
the big factors with offset (besides fender clearance) is that you do  want to 
line up the center of mass of the wheel/tire combo right over the top of  the 
hub to the extent possible.  But as the wheel gets wider, even  when you keep 
the center of mass lined up, you might still end up with a  longer "moment arm" 
(essentially, a longer distance from the hub  plate to the outside edge of 
the tread  -- measured, of course,  parallel to the axis of rotation -- not 
radially from the center of the hub to  the circumference of the tire).
 
Lengthening the "moment arm" will increase the stress on the wheel  mounting 
points irrespective of whether the wheel and tire combo  is weight-balanced 
over the top of the hub.  So when deciding on  offset, there are some potential 
compromises to consider between perfect  balance, the length of the "moment 
arm" and the constraints imposed by the  design and location of the adjacent 
suspension and body components.
 
Cheers,
Mark LaBarre
84 atx 135k