How does tire size affect speed sensors?

Answer 1

The speed sensors are calibrated to accurately reflect the vehicle's speed, based on the stock tire size. If you use a smaller size tire, then the wheels will make one full rotation, faster than the stock tires. This will in turn make your speed sensors read faster than you are actually going. If you use a larger tire, then the wheels will make one full rotation, slower than the stock tires. This will in turn make your speed sensor read slower than you are actually going.