Ned Simmons wrote:

In any case, I just can't accept that the car travels anything other
than 2*pi*r per rev (as before, r is the distance between the axle and
the road), regardless of what the tread does.

As I explained in my previous post (and as others have subsequently
explained), the equation c=2*pi*r applies only if (a) you're dealing
with a circle and (b) r is measured from the center of the circle.
Neither of those are true in this case. Why would you expect to be
able to use that equation when neither of the basic premises are met?

Think about it from the standpoint of torque.

Sorry, but an analysis of the physics isn't going to do you much good
unless you first get the geometry right.

Bert