I had 245 70/17 on my truck and just purchased 265 70/17. The diameter difference is 1.1". How much will it throw my speedometer out? I know the difference shouldn'be too great, but I would like to know the difference.

 

Nevermind. See what you find when you actually look.

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

Speedo is 3.6 MPH too slow. When you read 60 you are actuall doing a little under 63. I can live with that.

 

It used to be where 3% was an acceptable variance for a speedometer. If your off 3.6 MPH, then you may want to have the dealership adjust the setting in the computer.