I think Kevin and I are saying the same thing with slightly different semantics. When we did "on the car" wheel balancing back in the 1960's, one of my first jobs at Dad's shop was "driving" the car while one of his mechanics did the balancing. With one rear wheel off the ground, I'd hold a steady 30 MPH on the speedometer- - - -which ran the wheel at 60 MPH due to the multiplier effect of the differential gears. That's something to remember if you're ever trying to "rock" a vehicle out of a mudhole or a snow bank- - - -If only one wheel is turning, the spinning wheel is traveling twice the speed that's showing on the speedometer!
Jerry