MPG's w/oversized tires

[Field Scout]

I was thinking about my MPG's on my new 08 F150 Supercrew 4x4 and decided to try and figure my true MPG since my tires are larger than the stock tire (not by much, 265/70/17 vs 255/70/17) this makes me go 1 mph faster @ 70. It's a little unscientific but it works for me. I reset the trip in my truck and on my GPS and it works out that every 5 miles I drive by the truck odo I actually travel 5.2 miles so at 400 miles on the odo I take 400 divided by 5 gives me 80 now multiply by 1056 ( 2 tenths of a mile) giving me 84480 then divide by 5280 ( 1 mile) giving me 16. Thats 16 additional miles I actually traveled past what the truck odo reads so I actually drove 416 miles divided by X amount of fuel for real MPG on my truck, what I've noticed so far is about an extra 1 mpg so for all who have 35's, 37's etc. you may not have dropped as much mpgs as you thought you just need some new math for your figures.

Maybe know one cares, but thought I'd pass it on.

Steven