speedo not calibrated

[03knight]

i bought the car over the summer and i just used my GPS and its off about 3 or 4 mph .why would this be???

[CBT]

Hmmm.....have you tried the search function?

[Phrog_gunner]

I'd check your tire size, 4.10s would probably throw the speedo off more than that?? One of the guys with 4.10s will prob chime in here soon if I need corrected.

[PonyUP]

What mods have been done? Gears can throw off the speedo, also what size tires are you running front and rear? If the proper ratio isn't maintained, that can throw it off too.

Former can be fixed with a tune, the latter can be fixed running the proper tires


Pony seal of Approval

[RF Overlord]

Wrong size tires on the rear.

[mgmsleeper]

Mine is off via gps too but I have proper tires and stock gears

[MOTOWN]

Your gps may not be accurate(is it set for miles, or km), find your favorite patch of 1320 feet and check it against your speedo

[fesifisky]

I have a slightly smaller tire in the rear(Town Faire Tire had a good deal) and it threw my speedo off between 3 and 4mph, like others said, that's a likely culprit.

I also have 4.10s, but until recently had a chip to correct the speedo, now I think it's off by close to 20mph, so it doesn't sound like taller gears are causing this. just my 2 cents.

[mtenderenda]

Yep, it could be a different gear ratio or tire size...I just changed my gear to a 4.10...Its off by 5 mph...

[screamn]

Tire size is the culprit for mine being off btwn 3-5 mph. I got stock size frnts and 255/45R18 rear.

[CBT]

i bought the car over the summer and i just used my GPS and its off about 3 or 4 mph .why would this be???

So are you going 3 or 4 miles an hour faster or slower?

[TFB]

Back before everything had a computer, speedos almost always registered faster than the vehicle was traveling... At 60, was often as much as 5mph...

[EMAS]

As mentioned above from the factory you'll usually find that the speedo reads a little off. The laws say that your speedo can read faster than you are going but never slower. Depending on your GPS it can be off a few % too. I know mine is confused slightly by hills. I can set the cruise, have the needle pegged right at the center of the line, from which it doesn't move, but as I go up an incline the GPS reads slow and then going down it reads fast. Of course the tires are another factor within a given trade size from brand to brand and even different models within the same brand can have slight differences in revs per mile.

[03knight]

my speedo is reading 3-5 mph slower, i live on base and the police has a radar machine sitting on the side of the road to tell ppl how fast your going and i always have to go 23-24 mph to go 20mph

[03knight]

235/50 and 245/55 rears are my tire sizes

[tbone]

My MM and Explorer both are off about 1.5 mph compared to GPS.

[EMAS]

Well if we are talking about that low of a speed then that is not unusual to have it that far off as that is not considered part of the critical range. Mine is similarly off at that low of a speed but at 60 it's only off by about 1 MPH.