I would say it depends on the tire size you put on to whether its a coincidence or not. I for get my size but I think its 225/60-H16 (H is the speed rating). In my case we have cops who set up these raidor trailors that post how fast the on comming trafic is. If they are on a long enough road we use them to check 1/4 speeds Anyways they stuck one near my house and I made a dozen passes by it at different speeds which lead me to believe my speedo is off by 4-5 mph slower than what my speedo says. So it really don't bother me that much to mess with getting it adjusted and I love my tires to much to change them out either