WrenchCalcTire, gearing and engine calculators

Tires & wheels calculators

Compare tire sizes, convert metric sizes to inches, and see what a size change does to the speedometer and gearing.

Tire size calculator

Compare two tire sizes: diameter in inches, sidewall, revolutions per mile, speedometer error and the axle ratio to match bigger tires.

Before you change tire size

  1. Find the original size. It is on the placard in the driver’s door jamb, with the recommended pressures.
  2. Compare overall diameter. Within about 3% of the original keeps the speedometer and safety systems close to how they were set up.
  3. Check the load index. The new tire should carry at least as much as the original.
  4. Check clearance. Width and diameter both matter at full lock and full suspension compression.