How does tire size affect the reading of my speedometer?
A taller tire has a greater circumference. That means given the same number of axle revolutions, the vehicle will travel faster than with a shorter tire. The speedometer bases its reading on revolutions and assumes the tire is the correct size. Basically a shorter tire will indicate that you are going faster than you are. A taller tire will cause the speedometer to read slower than your actual speed. Please see our tire size error calculator where you can compare different size tires and see the effect.
