Does anyone know if the tire pressure monitor goes nuts when you switch wheels/tires to aftermarket ones when it doesn't get a signal? If so, does anyone know if the sensors can be retrofitted to aftermarket wheels? Thanks guys, this forum rocks! (headbanging smiley)

The sensors are in the brake system, not the wheels. You don't need to do anything to change out wheel/tire combo.

To my best understanding, the sensors calculate relative tire diameter based on individual tire speed. If one tire is lower in pressure, it will rotate faster than the others, signaling the warning light.

Hope this helps.