http://www.dakota-truck.net/TIRECALC/tirecalc.html I have a question though. This tells me that with me going from 215's to 31's My milage will show greater over a period of time. So they are telling me that after 50,000 miles of running this size tire my odo will actually show 90,844 (not including the milage already showing on the odo) so it will actually show 40,844 more than I actually drove. I thought it was opposite. I thought the more milage driven it would actually show less on the odo. because it actually take 1 1/4 revolutions to equal the single revolution of the smaller tire. So I figure the actual milage would be larger than what is actually showing. Am I making any sence?

 

Perfect sense. If you increase your tire size your mileagecovered should be less because it is taking less turns of the largertire to cover the same amount of space as the smaller one. Did you fill out the form right and put the smaller tire size in for "Tire A" and the larger one in for "Tire B?" It works ok for me.

 

lol.

 

I got it. I put it in right, I was just thinking bass ackwards.