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%.

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

Chainring Teeth

Sprocket Teeth

Cadence

Wheel Circumference

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 gear ratios from chainring and sprocket tooth counts.

Convert gear ratios to gear inches for comparison.

Calculate distance travelled per pedal revolution for any gear.

Compare chainring sizes and their effect on gearing range.

Analyse cassette tooth counts and gear jumps between sprockets.

Last updated: 2025-02-20

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