Pinto Car Club of America

I just went from 185/70/13 wheels to a 225/60/15 and as expected my speedometer is off, by how much I don't know but judging by this site http://www.miata.net/garage/tirecalc.html (http://www.miata.net/garage/tirecalc.html) it should be about 5 or 6 MPH slow, plus I timed how long it took to travel one mile at 50 and it took about 65 seconds so 5 MPH difference sounds about right.

My question is what number of teeth speedo gear would I need to correct it? I haven't checked what color it has in it yet but its got the stock 3.00:1 rear and 4 speed.

Thanks

This is not precise but should get in the ball park.  Since your speedo is off ~10%, install a cable gear with 10% fewer teeth to speed up the indication.  Odds are there will not be a gear right at the 10% less teeth mark, so you have to decide which way to bias the indication.  I like to have the speedo read a little high to avoid trouble with tickets (also gives false sense of better mpg).

Speedometer gear listing and calculator here, page 182 (search speedometer to get there quickly):

http://www.fordracingparts.com/2011-catalog/ (http://www.fordracingparts.com/2011-catalog/)

Mike