When I put in my new tire size, 28.9 inch with 4.10 gears (original ratio), the calculated tire size goes to 29.32 inch. My brother has HPTuners also and when he put in a tire size of 33.5 with 4.10 gears, it calculated it at 31.8, when I input it on my program it calculates 33.99 inch. Why does the tire size recalculate? And why the difference between our programs?