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Bike Gear Calculator — Ratio, Gear Inches & Speed
Gear ratio, gear inches, roll-out, and speed at any cadence.
Speed across the cadence range
Ratio, gear inches, development, speed
Four numbers describe a gear. The ratio is simply chainring teeth divided by cog teeth — how many wheel turns you get per pedal stroke. Gear inches multiplies that ratio by the wheel diameter, the old penny-farthing measure still used to compare gears. Development (or roll-out) is the distance the bike travels in one full pedal revolution. And speed follows once you add a cadence.
Why tyre size matters
A bigger tyre rolls a little further per revolution, so the same 50×14 is fractionally taller on 32s than on 23s. The calculator uses the rolling circumference of the wheel-and-tyre you pick, so the development and speed reflect what you actually ride.
Finding a cadence you can hold
Most riders settle around 85–95 rpm on the flat. Slide the cadence and watch the speed table to see which gear lets you spin comfortably at your target pace — a gear that forces you below ~70 rpm on a climb is a sign you want an easier ratio.
Questions
What are gear inches?
Gear inches express a gear as the diameter of the equivalent direct-drive wheel — chainring ÷ cog × wheel diameter in inches. Higher means a bigger, harder gear. It is a handy single number for comparing very different setups.
What is development or roll-out?
It is the distance the bike travels for one full pedal revolution — gear ratio × wheel circumference. Combined with your cadence, it gives your speed.
Does tyre width change the result?
Slightly. A wider tyre has a larger rolling circumference, so the same gear rolls a touch further per pedal stroke. The calculator uses the circumference of the wheel-and-tyre you select.