[Carbeaux]

Difference is 3.3%, so when your odo says you've gone 3,000 miles on the smaller tires your speedo would have read 2901 on the other tires. You're making the odo read more miles for the same actual distance traveled.

You sure your OEM are 275/70/18 and not 265/70/18?

Here's a link to a tire size calulator you might find useful.

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

 

[Jiro]

Yeah, Pro-4x stockers are 275/70/18. I have 275/60/20 right now. Thanks for the quick and accurate response Carbeaux