[nkaminar]

Werner,

Thanks for responding.

The fact that there is a phase shift above the critical speed was a real surprise to me when I took a dynamics course in college. It does not make sense to someone without the technical education.

Every dynamic system, such as a rotating tire supported by a spring system, has a critical speed where the deflection caused by the unbalance is greatest. Below this critical speed the heaviest part of the tire has the greatest radius and the balance beads will migrate to that spot and make the unbalance worse. But above the critical speed the situation reverses and the heaviest part of the tire has the smallest radius and the lightest part has the biggest radius. So the balance beads will migrate to the lightest part of the tire to balance out the heaviest part. The beads migrate due to the circumferential force. Gravity does not enter into the equation because the circumferential force is a lot greater than gravity, at least for the Model A tire.

I don't know at what speed the critical speed is in a Model A tire, but suspect it is somewhere around 30 mph or maybe higher. It will depend on the car too, such as how stiff the springs are and what condition the dampeners (shocks) are in.

I know it does not make sense from the perspective of flinging a weight around with a string, but the fact that there is a phase shift above the critical speed has been proven many times.