If you hold one wheel stationary and allow the other one to spin free, the action of the spider gears doubles the speed indicated on the speedometer. When we used to do "on the car" wheel balancing, my job used to be to "drive" the vehicle at an indicated 30 MPH in high gear while the guy at the wheel used a clamp-on device to monitor vibration and attach the weights. It was very effective, as the entire assembly, wheel, tire, and brake drum got balanced all at once. The actual wheel speed during that procedure was 60 MPH. On front wheels, we used an electric motor driven wheel spinner.
Jerry
