PCC cars used several different types of rubber insulated wheels over the years. The purpose was to prevent vibrations from the steel wheel running on steel rail from being transmitted into the car body and to reduce noise.

The original version was known as a resilient wheel. It was followed by the super-resilient wheel. Both used sandwiches of rubber and steel between the wheel and the hub. Interurbans Press #64 mentioned earlier has good drawings of the different types of resilient wheels.

To reduce maintenance expense some systems reverted to a solid steel wheel on a steel axle on PCC trucks. I seem to remember a variation that used a plastic insert shim between the wheel and the axle that would reduce vibration but not as much as a resilient wheel.

All three types of insulated wheels used jumper wires about six inches long between the wheel and the hub to pass electricity. Heavy stranded wire ran from the inside of the wheel to the hub following the countour of the wheel. I have seen both two and three jumpers per wheel.

The outside of the wheel is known as a tire. They were made with different tread contours from narrow streetcar wheels to compromise tread that was between streetcar and AAR railroad wheel contours. Muni #1016 at Western Railway Museum had Muni streetcar tread tires replaced with compromise tread tires from Shaker Heights cars as part of its restoration. This allows it to operate on former Sacramento Northern track.