When you mount other tires under your car, you might get a deviation on your speedometer.
How much exactly this deviation is can be calculated here below.

Tire Size Height Perimeter  
Standard / R cm cm  
New / R cm cm
  Difference cm cm %
Standard Speed (on speedometer) km/h km/h km/h km/h
New Speed (effective) km/h km/h km/h km/h

This calculation uses the following formulas :
Tire height = Tire width X Series / 100
Height = Tire height X 2 + Rim size X 25,4
Perimeter = Height X Pi



Updated : februari 13, 2005 - 05:00 CET