: Speed and distance calibration

06-11-06, 04:43 PM
I recently bought a new 2006 STS with the adaptive cruise and the car had 17" wheels on it. I asked and the dealer gladly changed them for the 18" wheels and tires(for a fee).

My problem now is that the trip meter and speedometer seem to be wrong as I timed the distance between mile markers several times at 60mph and after another dealer checked it and said it was "right on" I used a gps to check the speed and found it be about 3mph off. So, the miles accumulated will be wrong and probably the calulated gas milage too. Has anyone else experienced this? Is there a fix?

06-11-06, 04:57 PM
I would guess that ~5% difference between your STS instruments and your GPS would be within normal tolerance levels (but I could be wrong). You might check in with your State Patrol to ask what their data reveals. Be interesting to perform your comparison with a different brand, ie Lexus, etc

Benjamin Simon
06-11-06, 06:55 PM
The size of the tire should not change. Now you just have less tire and more rim.

06-11-06, 10:29 PM
Thanks for the quick responses. Didn't expect to see any responses until at least tomorrow.
If I understand the responses so far, the opinion is that if the car is off now it was off before with the 17 " wheels.
If that's so, I'm really surprised that it would be so far off.
I sometimes like to push the speed at which I can drive to the limit - in some areas it seems to be four mph over the posted limit and sometimes less. If I go by the HUD with cruise set at 73 or 74, I could be traveling too fast and get ticketed!
Seems odd to me that a car with so much technology would not be much closer to actual. The navigation seems to be correct and there is a calibration button there. If nothing else, seems that the car could get set by the GPS on the navigation system. I alway thought that speed measured by GPS was reliable. And anyway, The clocked times and the speed by GPS agree. I really don't understand what is going on here. Hopefully, someone can set me straight. Perhaps I need to take the suggestion of having a cop clock me. At least I would know exactly where I stand.

Has anyone else out there checked their actual speed against the STS speedometer?