What gear do I need for 40 km/h?

At 90 RPM on 700x25c tyres, you need a 50/14 (3.57 ratio) for 40 km/h. At 100 RPM, a 50/15 (3.33) will do it.

What gear for climbing?

For a 10% gradient, most riders need a gear ratio below 1.0 (e.g. 34/34 or 34/36). This gives about 8-12 km/h at 70-80 RPM.

Speed is directly proportional to cadence. At a constant gear ratio, increasing cadence from 80 to 90 RPM increases speed by 12.5%.

bikecalcs.uk

Calculate your road speed in any gear at a given cadence.

Chainring Teeth

Number of teeth on the front chainring

Sprocket Teeth

Number of teeth on the rear cog/sprocket

Cadence

Pedalling cadence in RPM

Wheel Circumference

Tyre rollout in mm (700x25c ≈ 2105, 700x28c ≈ 2136, 650b/27.5 ≈ 2090)

Speed (km/h) = Gear Ratio x Wheel Circumference (mm) x Cadence (RPM) x 60 / 1,000,000

The formula calculates distance per pedal revolution, multiplies by cadence to get distance per minute, then converts to km/h.

Calculate required cadence for a target speed in any gear.

Calculate gear inches, development in metres and speed at 80, 90 and 100 rpm for any chainring, cog, wheel size and tyre width combination.

Calculate distance travelled per pedal revolution for any gear.

Calculate gear ratios from chainring and sprocket tooth counts.

Find the ideal single speed gear ratio for your terrain.

Last updated: June 2026

All calculations are estimates. Always verify results and consult a professional bike fitter where appropriate.