Compare two tire sizes for diameter and speedometer difference.
Tire diameter combines the rim plus twice the sidewall height, which depends on width and aspect ratio. The percentage difference tells you how far the two sizes drift apart. Changing tire diameter by more than a few percent skews the speedometer and odometer and can affect gearing and ground clearance.
Tire Size Comparison
Diameter = rim x 25.4 + 2 x (width x aspect%)
Diameter = rim x 25.4 + 2 x (width x aspect%) Tire diameter combines the rim plus twice the sidewall height, which depends on width and aspect ratio. The percentage difference tells you how far the two sizes drift apart.
Changing tire diameter by more than a few percent skews the speedometer and odometer and can affect gearing and ground clearance.
This calculator takes 6 inputs: Tire 1 width, Tire 1 aspect ratio, Tire 1 rim, Tire 2 width, Tire 2 aspect ratio, Tire 2 rim. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.