As always, it's what you like. I have stock sized tires (265/70R17's) and mine is off also about 2-3 mph. Says I'm doing 423-43 at speedometer indicated 45mph. Drives me buggy! I just tried to "fix" it. When I worked at a dealer (Albany dodge) their scanner (at the time 2002) could fix my Dakota, so I did. Verified it, as my close friend (a County Mountie) used his radar gun to verify. Just bought my own home scanner (Innova 7111) and it is supposed to be capable. So tried to correct it yesterday but no luck. Tire on truck is a non O.E. brand but as stated OE size. They do have a screen that I am supposed to use, but I could not get it to work. Not the scanner BUT ME! When I did the Dakota, I got the actual rolling dia. of the tire and just enter it-DONE. This scanner (much less expensive than dealer type) has many sizes and brands of tires listed that I can pick from to tell the truck this is what it has. However, it already knows what is on the truck Size wise), so that did not help. So I put a level off the top of the tire, measured to the floor to get the rolling dia. (30.5 inches) x 3.14- pie to get the circumference - 95.77 or approx. 95 3/4 inches. Went to put that in and of course it wanted it in mm! (2432.558 mm) tried to put hat in and it said (you dummy that's the wrong number! So I assume it does not need or want the decimal point or numbers after it. But now the battery on the truck getting low, so cleared all the codes I set somehow (the info on the tire size is put into the Body Control Module. Truck on a trickle charger overnight will try again and just enter the 2432 mm. So all of this just says that some of us are just real goofy about non necessary "stuff". Now I will be on a "mission" to correct it, when it would be so much easier to think - you idiot you're going slower by a mile or three an hour than the speedo says - live with it. BUT I WON"T!!!!!!!!!!!!
