Speedometer Problometer
 

So I always have questioned the accuracy of my Speedometer, and other people have told me that I was driving 50mph and my speedo said 55. At 60 they tell me I'm driving 55. But I followed my Mom in her caliber (and I know that speedo is incredibly accurate, from passing a speed sign). and she went 55 and mine said 55. So I'm beginning to question how accurate it is. I've passed one of those speed signs one time, and my speedo said 45 but the sign said I was doing 43. I'm guessing it's about 5mph off at 60.

Question is, how do I test this? I'm just glad its overrating my speed, and not underrating it. I know that the best way would probably be take it to a dyno, which I have no idea where one would be. And how much would it cost to dyno the thing?

If you had a gps it would be pretty easy, but there are a few tricks:

1. Go out on the highway and use the mile markers and compare to your odometer / trip meter and find the difference.

2. Plot a route on google maps, follow it, and see the difference from the google maps mileage and your odometer / trip meter.

Most people's speedos are a bit off, good luck, :p

I have GPS, so.. there we go! I've done a mile marker thing to see if the odometer is also reading wrong and it was pretty accurate.

EDIT: how do I adjust the speedo if I find it to be off? is there a calibration thing I can do?

If it is off, then there's really not much you can do about it. On older cars I've heard they are often off because the manufacturers only made one speedo for various cars with different wheel sizes and things...So it's likely not adjustable.

Well I heard that you can adjust a speedo or tach to accommodate a different speed, ie. take a speedo and adjust it for every 2mph it reads 1mph, so that you can read it as if it says 120 it's really 240. Although those were after market speedo's and tachs, so I'm not sure. wouldn't the cable be adjustable?

On my old cable speedo (electronic now) I know it wasn't adjustable. I spose you could have put a different gear on the speedo itself inside the tranny, but honda only made one gear, so you'd have to get one custom made, :p

I'll consult my grandpa, he was a mechanic for over 30 years, I don't know if mine uses a cable one or not, but a lot of things on this SUV were electronic, and that the Idle speed isn't adjustable. I mean, it was a 30grand vehicle when it came out, I'm sure they would use more electronic stuff since it was supposed to be a luxury SUV. I'm just glad I got mine for 2grand :D It WAS the 90's tho...

It's too bad your Jeep wasn't a '96. The ScanGauge can be dialed in as a very accurate speedometer.

well, I used the GPS and it said it was only about 1mph off. I used cruise to rule out the driver and it was only 1mph off. not too bad

if the tire size is diff from stock you may be able to buy new grears to mach the diff. tires. i have done it a ford and a gm.