coefficient of traction

He talked with gusto about "proactive urethane," the "maximum coefficient of traction" and something called a "flared ball track."

The coefficient of traction is defined as the usable force for traction divided by the weight on the running gear (wheels, tracks etc.) i.e.:

When this is the case, traction is often expressed as the ratio of the maximum tractive force to the normal force and is termed the coefficient of traction (similar to coefficient of friction).