JML

I ran 2 tanks of gas thru my truck and avg 22.4 mpgs over 600 miles or so (didn't run each tank empty but always filled all the way up).
When I go by radars, they say I'm going faster than my speedometer. This must be do to the larger than stock tires (265/70/16 vs 225/75/15)
According to web calculations my speedometer is 8.2% slow
So doesn't that mean my odometer is 8.2% shy and I'm getting 24.67 mpgs?

regularguy412

Looks about right to me. Not knowing which particular brand of tire you have, I chose to compare revolutions per mile of the Michelin LTX M/X tire in the two sizes you mentioned. For that particular tire, I came up with the 265's being 8.1% larger. So yes, you are traveling 8.1(2)% farther than your odometer shows.

And stop rubbing in the 24.67 mpg. JK

Mike in AR

tulsa_97SR5

The only pieces missing are the true measurements of your tires, and if the speedo was spot on before the swap. You should be in the ballpark with that adjustment though. Tire rack usually lists true measurements on the spec sheets, see if they have your tires listed.

AxleIke

You are 8 percent off. An easy way to calculate this is to take your new tire size and divde it by the old. You new tire is 30.6 inches in diameter, and your old was 28.3. This is about 1.08. Multiply your mileage between fill ups by 1.08, and then divide by the number of gallons you put in.