I just got some bullits with pirelli's on my 2000 GT. This was my first upgrade. I have only had the car about 2 weeks but I couldn't live with my old rims.

http://i7.photobucket.com/albums/y26...87/Rims011.jpg

The speedometer is off by a very slight amount because of the size change. I think it is off by like 1.5 miles and hour at 30mph. How would I go about resetting the speedometer?

 

If it's only 1.5 mph, I wouldnt worry about it personally. Mine's off by 30 mph. The speedos arent exact anyways, just close. So who knows maybe it shows the correct speed now. Seriously though, if you need it done, take it to any speed shop or Ford and they can do it for you for some bucks. I think its like $60 here.

 

You'd need a tuner or a speedcal. Either would be a waste of money for a 1.5mph difference. I wouldnt worry about it. I dont even see how you noticed it?

 

Mine's off my 2 mph at 30mph and I'm 100% stock...in what matters for a speedo, anyway.

 

I didn't notice the small difference. I calculated the difference and the total diameter of the tires is 1 inch bigger. When I am going 30mph, my speedometer says 28.90. When I am going 60mph, my speedometer says 57.79, So its not really that big of a difference. But I think while driving at constand speeds, I may get slightly better gas mileage because my car thinks that it is working less to maintain that speed. In theory that is true anyway.

 

What are the tire sizes you're dealing with? You won't notice the difference in mpg...too many other variables take afect over the period of a tank of gas. You may actually decrease, depending on the rotational inertia of your new wheel/tire combo.

 

Hmm...I dunno if that theory is much more than just that.......a theory. How could the car think it is working less to maintain that speed? The speedo doesnt affect the way the computer is set to run. The computer will make any necessary adjustments, but takes no cues from the speedometer as far as I know. If you went to a bigger rolling mass, you may **slightly** decrease in gas mileage and your speedometer will indeed be off by a bit, but on a 1 inch diameter difference, I hardly think it's something you should notice.

[sm=smiley20.gif]

 

Mine is way off. When Im going 70, it says 140. I never changed my rear end after the swap, so that why.

 

I went from a 235 55 16 to a 235 55 17.