Thread: Speedometer Recalibration

Hello all, I have a 2000 GTP I just picked up. The previous owner replaced the stock wheels with 17" ones and, obviously, the speedo is off. Seems to be a fairly consistent 5mph off, if I base it on my GPS's speed. Now, I am more than comfortable with simply subtracting 5mph from my speed when driving, but it is actually my wife's car and she will probably forget, a lot. Is there any effective way to recalibrate the speedo to make it more accurate?

Thanks, I appreciate the help.

uhm get your gps and just move the needle

Thanks guys. By "tune" I assume you mean a tuner?

Can't just move the needle, wouldn't fix the HUD.

Thanks again

didnt know you had a hud

Originally Posted by Jteske88

didnt know you had a hud

Sorry, wasn't trying to be snarky there (I usually am, I just wasn't TRYING that time).

Originally Posted by gmpowered

Use this to determine how far off the car is. Tire size calculator

A tuner wont have a "table" but you will be able to correct the 3% it may be off. It wont just affect the speedo it can change shift points tcc lockup ect ect if the tires are that far off.

Other than the wife forgetting about the speed difference, I was also worried about this. I mean, if the computer bases things off the speed and the speed is wrong....

Now I just need to find someone to help with tuning. Having never done this before, what is the typical procedure? Is this a bring it to a shop sort of thing or find someone who likes beer and knows what they are doing?

Thanks

Looks like I'm off by 6.2%, based on the calculator.

Thanks again everyone

You have you have to change the tire size in the bcm as well which can only be done with a tech2.

Also note theoretical diameter is not what the pcm/bcm use for tire calcs either.