Gear Ratio Calculator

Compare stock and new tire sizes with the original axle ratio using tire-diameter geometry.

Stock tire

New tire

Stock axle ratio

—Effective ratio

—Ratio to restore stock

—Diameter change

—RPM change at same road speed

—Theoretical tire-diameter relationship only; drivetrain behavior also depends on transmission, converter/clutch, load, and real rolling radius.

How to use this Gear Ratio Calculator

Estimate effective gear ratio after changing tire diameter and the ratio needed to restore stock gearing. Enter your values above and the result is calculated directly in your browser. No account is required.

Fast answer, clear inputs

This tool is built around one job: give the answer quickly without forcing a signup or hiding the result. Related tools are linked nearby when the next calculation or conversion is useful.