Tire Size Gear Ratio Calculator

Fitting taller tires changes the gearing whether you meant it to or not, because the tire diameter divides everything between the engine and the road. Enter the size you had, the size you are fitting and the axle ratio on the door sticker, and this returns the ratio the old axle now behaves like, the ratio that would restore the original gearing, the nearest one actually sold, the engine rpm before and after at a cruising speed, and the speedometer and odometer error the change introduces. Both sidewall markings and flotation sizes are read as typed, or you can enter a diameter you have measured. It uses free diameters, so the loaded rolling diameter will be one to three percent smaller.