157dB

Stock 17 and 18" rims have the same Revs Per Mile as the tires are different sizes.
You can swap OEM 16s for OEM 17s or OEM 18s and not need to change the Revs
Per Mile setting.

Qusus

Rationally, I know this is a joke but I'm wishfully thinking that it isn't so my speedometer can be fixed just as easily.

Budman2K

This is true as long as the diameter of the tire remains the same. As the diameter of the tire decreases the revolutions per mile increase, and as the diameter of the tire increases, the revolutions per mile decreases. Please, correct me if I'm wrong.

Sprzout

I noticed it about a year ago...35-40 mph, my car's speedo was dead on accurate. At 70-80 mph on the speedo, my car's speedo is off by about 5-7mph (I'm going anywhere between 65-75 mph per GPS, but the speedo reads higher).

I figure I'll just fix it when I do the tune. Fire & forget, I guess.

Argonaut

Wow - I thought it was just me. I installed 4.10s a while back, used the XCal2 to reset the rear diff and also put in the rev/mile for good measure. Speedo has been off just like you guys say, in the higher MPH ranges. Someday when I feel like it I'll probably mess around with the settings in the XCal, see if I can get it closer to reality.

Qusus

Good to know other people are having this problem.

Anyways, here's an update:

Took my car to the dealer today to have em look at it. They said sometimes it doesn't come from the factory with the right calibration and it's probably just a simple software fix.

I didn't have time to leave it with them but if your cars are still under warranty I'd reccomend you do that. Some people might not think it's a big deal but keep in mind that your odometer might be reading off too. This means that there's anywhere between 5-15% extra mileage on your car than there actually is; not something to scoff at for resale value etc. That's my major concern anyways.

Stokestack

I'm having this problem on my '96, but it's intermittent.

I've noticed the same disparity that you guys are talking about between the speedo and the GPS for years, but the other day I was supposedly going 90 in traffic. No way.

Sure enough, the GPS indicated 73. This has happened a few times on the highway, the speedo indicating way too high a speed. In most cases, though, it's shows a nearly accurate value.

The intermittence of the problem makes it a bigger deal, since I have no idea when the thing's right. A 17 MPH difference isn't acceptable. Has anybody seen this situation?

Thanks!