Bike Speed and Cadence Calculator

In short Speed, cadence and gear are three quantities with only two degrees of freedom: fix any two and the third is decided. Each turn of the cranks moves the bike forward by the development of the gear — the ratio times the wheel circumference — so speed is simply development multiplied by cadence. In a 50 × 16 on 700 × 25 tyres, one crank revolution covers 6.60 metres, so 90 rpm is 35.6 km/h. Turn that around and it answers the more useful question: what cadence does holding a given speed in a given gear demand? Most riders settle somewhere between 80 and 100 rpm, and a figure far outside that usually means the gear entered is not the gear being ridden. What this does NOT tell you is how hard it will be. It is pure geometry: no wind, no gradient, no rolling resistance, no rider. The wheel turns that gear at that speed whether you are freewheeling downhill or grinding into a headwind, and the effort question needs a power model instead. Treat this as the answer to "what will the cranks be doing", not "can I hold this".