That's because the outside diameter of the 20" tire is larger than the tire on the 18" wheel. Its all part of using bigger wheels, unless you compensate with a reduced tire sidewall height (a.k.a. aspect ratio), or get a tuner that can program the speedo to correct for the change in tire diameter.According to my friend's speed laser and my gps, the speedometer on my car is 3mphs off
I think going from 18 to 20 wheels caused this
How am I suppose to fix this ? Do I go to the tire store where I bought my wheelz from ?