MustangGT75

I just bought a 95 mustang and the speedometer is off about 10 miles when i am really doing 60. The guy told me he put a chip in it and the engines computers been reprogrammed. Would that cause it to be off that much though? How would i go about fixing this problem so my speedometer is accurate?

powerkord

does it have stock wheels? stock gears? somebody might have changed the gears and never put in the speedo recalibration gear.

MustangGT75

I am not sure if the gearing has been altered or not and the wheels arent stock they are a size or too bigger, i think 17's or 18's. Is there any way i can tell if the gearing has been altered cuz thats something i am curious about. After all i dont think think just tires would throw it off that much.

powerkord

Id say its because of the wheels, most definatly. At higher speeds youd be suprised how much of a difference larger wheels make. as to what to do, dunno never had that prob on a car, only bikes. an expierenced mechanic will know what to do

wildstang87

you need speedcal for the 94+ cars, you can get one for $99 bucks at www.dallasmustang.com... hope this helps. most likely yours is off b/c of the rim tire change. go read the sidewall of your tires and let us know what size they are, and i will tell you if thats what the problem is.

fordguy17

to check for aftermarket gears, jack up the rear of car (use jackstands) and mark the driveshaft in one spot. white out works.

rotate the tire on complete time and count how many times the driveshaft goes around. stock should be anywhere from 2.73-3.08.

if it has aftermarket gears it will be anywhere from 3.55-4.10.

MustangGT75

The tires are 17 inches and i just looked at my v6 and those are 15's. Would the tire size cause the speedometer to be off that much? I am going to test my gt later to see what its geared at but if they are stock how can i readjust the speedometer so its correct with the 17's.

wildstang87

you need to see what size 17" tires they are like 245/45/17 or whatever. if thats the case then that isnt your problem as alot of the gts came with 17s. also how do you know the speedo is off 10MPH at 60??? drive beside someone else with a newer vehicle and compare your speeds.

MustangGT75

i already had my bro in law follow me home from work, my speedometer said 60 and a little better and my bro said i was going 50.

wildstang87

ok, see exactly what size tires are on it... 245/45/17 etc... i doubt that will make it 10mph off at 60mph though. you might have a set of gears in that ride.