Know your gear.
Dial in your setup.
Compare gearing and crank length.
Find the numbers behind your next change.
Current setup
Use an estimated wheel size
Nominal sizes are estimates. Measure your rear tyre at riding pressure for a more accurate comparison.
Proposed setup
Use an estimated wheel size
Nominal sizes are estimates. Measure your rear tyre at riding pressure for a more accurate comparison.
6.1% more pedal force
With setup B, for the same driving force at the rear tyre.
Gear inches
Current Proposed
Rollout per pedal revolution
Current Proposed
Speed at 100 rpm
Current Proposed
A better way to compare.
Gain ratio
Includes your wheel, gearing and crank length. Higher gain requires more pedal force for the same force at the tyre. It does not predict your race speed or ideal crank length.
Gear inches & rollout
Gear inches compare wheel size and gearing. Rollout is the distance travelled in one full pedal revolution. Changing only crank length leaves both unchanged.
Measure your rear tyre
At riding pressure, roll the bike one full rear-wheel revolution with the rider’s weight supported safely. Measure the distance in millimetres and enter it above.
Formulas & calculation notes
Rollout = tyre circumference × front teeth ÷ rear teeth. Gear inches = rollout in mm ÷ π ÷ 25.4. Gain ratio = rollout in mm ÷ (2 × π × crank length in mm). Speed in km/h = rollout in metres × cadence × 0.06.
Pedal-force comparison assumes the same effective tangential pedal force direction and ignores drivetrain losses. Real performance also depends on fit, technique, cadence and power. The starting 20-inch example uses an estimated circumference, not a specific tyre model. About gain ratio ↗