alrighty, i recently got a set of 265 75 16 destination mt's and my old tires were the same size, but i'm noticing that before i would go one mile in sixty seconds exactly at 60mph and with the same size mudders i'm going one mile in 1 minute 3 seconds and noticing a drop in fuel economy of 3 mpg 17mpg to 14mpg. perhaps the tread is taller giving me an off reading on the odometer? i looked around the web for revs per mile and i'm getting 637.23 for this size. take it that it has increased a bit with these tires and not sure how much i would increase it by on my tuner. kinda stumped, any input would be cool.

 

were your old tires the same brand or style? Try going to the manufactur's siteand see if they have any specs on true OD or rev's per mile

 

Since you can only increase you Revs per mile by increments of 5 I would try 635 and then 640 and see which one is more accurate.

As for the gas mileage that small of a tire increase should not effect you mileage that much. I would check the tire pressure of the new tires and I bet they are low.

 

checked the pressure and they are fine. the tires i had before were pathfinder sport suv, i did have to take my front mudflaps off because the mt's were rubbing on tight corners, the old tires didn't rub. so i think there is a bit of size difference. couldn't find anything on pathfinders web site or firestones about it, i'll try 635 and 640 revs per mile tonight or tomorow and see what happens.