Jeremy

Isn't there a math formula to calculate the rotation of the tires depending on the size of the tires? If anyone can help me out that would be great, I'm 3mph off on my car. I know it's not much but it is annoying.

paulboy16

http://www.miata.net/garage/tirecalc.html

Jeremy

Cool, thanks man.

paulboy16

np

djl0657

Most speedometers come from the factory about 3 or so MPH in your favor (in other words, a reading of 55 might actually be 52). This is assuming that you haven't messed with your tire profile and made them larger or smaller.

Jeremy

I've put different size tires on them.

Action_Jackson

When I put on my 245/40's I noticed the speed off also. The guy at the tire shop said that it was the right size to keep the speedo right, but he was just doing it by rolling the new tire up against the factory. I thought it looked a bit shorter, but he said that once it was inflated that is should be right. In my area they have these signs that the cops drop off here and there which shows how fast you are going, and before the tire switch it was right on at 45mph. Now if I am reading 45 on the speedo it shows 42 on the sign. I guess I shoulda a waited for the 255/45's to come in, but I was in a hurry, and didn't want to wait. They are the perfect size to get the speed right.

Jeremy

I've got myself a handheld tuner so I can just do it myself.

paulboy16

im wishing i went for 245/45/18's too, but i like the fronts, so later on i might just get sum 265/40/18's for the rear