I know it's been said before

But I am unable to locate the thread on which my issue is located.

Here's the deal:
I went from stock tire size (29.5") to 31x10.50's with an overall diameter of 30.2" per Ian's instructions on calculating it. I am far from being good with math, so what I am trying to figure out is my actual gas mileage and odometer readings. Your help on this is much appreciated..... Thanks

Do you know about the tire calculator in the info section at the top of the page? It might help you out.

Yes, that is how I got my overall tire diameter calculated. Like I said, Im a math idiot and am not sure how to take the tire diameter difference and compute my miles per gallon. For instance, with my 30.2" tire diameter my X took 15.703 gallons of gas and went 230 miles according to the odometer.....