[Ernie Rogers]

Hello, folks,

Let's talk about an idea that came up once before but didn't get any discussion. The idea of measuring the rolling resistance coefficient by just bouncing the tire.

The rolling resistance coefficient (call it Crr) is closely related to the coefficient of restitution (call it CR). You get the coefficient of restitution by simply bouncing a tire--

CR = (bounce height) / (drop distance)

The quantities Crr and CR should be related by something close to this--

Crr = K (1-CR)

K is a "constant" that depends on the conditions--

How high you drop the tire
How much weight is dropped
Tire pressure and tire load

With some study, we should be able to determine the right test conditions and the value of K.

A bounce test might be something that can be done more easily than buying a rolling resistance test machine, and easier than doing a coast-down test, or using a ramp.

Additional point: A bounce test might also work for testing the efficiency of road surfaces.

I think I will pass this on to some teachers for possible thesis topics or a science fair project. You might pass the idea along if you think it has merit. There is probably an ASTM committee for Crr, and they might take an interest.

What do you think?

Ernie Rogers