Adjust MPG calculations with tire size?

[Airstreamer67]

One easy way to do it is to make the adjustment to the gallons pumped. This way, the odometer mileage stays consistent without need for complicated tracking, and the miles per gallons come out right.

In other words, if you are traveling 1.073 miles for every mile the odometer records as 1.000 miles, this means you are actually traveling 7.3% more miles than the odometer says you are. So, multiply the gallons pumped by 0.9320, and divide that into the odometer-reported miles traveled to get your adjusted miles per gallon.

Example: the odometer says you drove 400 miles and used 20 gallons, multiply the 20 gallons by 0.9320 to get 18.64 gallons, to give you a miles-per-gallon of 21.46. If your odometer had the correct mileage, the miles driven would have been 429 miles (400 x 1.073), which when divided by the 20 gallons pumped would give your the 21.46 miles per gallon.