How it is calculated
There is no wheel slip. Cadence is crank revolutions per minute. Take the diameter from the tyre-size calculator and convert it to millimetres.
Rollout = π × diameter × front / rear
Where the numbers come from
- Wheel diameter — unit in the field: mm
- Front chainring — unit in the field: teeth
- Rear sprocket — unit in the field: teeth
- Cadence — unit in the field: rpm
Example
A 700 mm wheel, a 50-tooth chainring and a 17-tooth cog, at 90 rpm on the pedals, give about 34,9 km/h.
Questions
Is 700c equal to 700 mm?
Not necessarily. 700c is a bead-seat standard. The outside diameter depends on the tyre and, with the rubber fitted, is often near 680–700 mm.
Several gears?
Calculate each pair of sprockets separately.
Gear inches?
Rollout in metres is already there. Gear inches = diameter in inches × front / rear.