Harold, Bart doesn't run a speedo cable......Because the car hasn't moved in god knows how long. JUST JOKING BART!!!! On a more serious note, I have 15" rims and tires on the rear of my gremmie WITH the speedo cable hooked up, and the trick to accuracy was to measure the circmfrence of the original 14" tires and make sure the new 15" tires were as close to that as possible. Mine are within 1/2" and the speedo error is less than 3%. 'The Mix'