So I just finished making a 500 mile trip from Maryland to Kentucky. My first fill up I did the math and the results said 13.5, but I did notice some issues with my tire size.

The math on my tire size differance should have been only a 3% differance so I never bothered plugging that into my mileage calculations, but the differance is really 10% that made a dramatic change in mileage.

My second fill up I got 17.5 MPG and that was doing 70 MPH using cruise through the mountains. Needless to say I'm pleased with the results and feel like an idiot for not paying closer attention to the real world Differance my tire size made