For what its worth.... When you go to bigger diameter tires than stock, you are throwing the accuracy of your odometer out the window. You are actually traveling farther than your odometer says. You now travel a farther distance, per each tire rotation. Soooo, you are probably getting better gas milage than you think, if you are using your vehicles odometer to figure it out. Somebody smarter than I am could probably figure out the change in 1 mile reading, when you increase tire diameter by 1,2,3 inches.