So I finally decided to check my distance on GPS vs Odometer. I run 31's. The Odometer said 3.5 miles while the GPS said 3.8. Doing the math I actually traveled 237 miles on my last tank rather than 219. That also means I'm getting better gas mileage than I thought, 14.24 vs 13.12. I guess I could change the speedometer thingy mabobber. But I'd say it's a win-win situation for me!