Free local bicycle gearing check
Count the teeth.
Know the rollout.
Use your own drivetrain and a measured wheel rollout to turn one setup into comparable gearing numbers before you change parts.
1 · Enter one drivetrain
A comparison, not a fit
Measure the tyre you actually ride.
Gear ratio is front teeth ÷ rear teeth. Development is that ratio × your measured wheel rollout. Gear inches express the same development as the diameter of an equivalent direct-drive wheel: development ÷ π ÷ 0.0254.
Measuring one wheel turn on the ground avoids guessing from a tyre label. Tyre pressure, load, surface, wheel slip and measurement method can still change the real distance. This page only compares the numbers you enter.
This calculator does not identify compatible parts, check chainline or chain length, model hub gears, choose a ratio for terrain, predict speed or effort, inspect a bicycle, or guarantee ride safety. See BikeCalc's gear-inches explanation ↗