You can buy Programmer to adjust your speedo for propper tire.yea, im sorry to say they did this w/o my knowledge until someone pointed that out to me yesterday. went from 17" to 20" rims and they gave me 275/45/20 kumho tires and took some off the bolt and never mentioned it to me. you can bet i'm goin over there tomorrow. speedometer seems to be showing 6mph slower than actual. seems the right tire could have avoided all this.