Bike gear converter
Convert gearing between gear inches, development and gain ratio. Pick your wheel first: the same sprockets give a different gear on a 29er than on a folding bike.
That's about the same as a cruising gear. At a steady 90 rpm that rolls about 30.16 km/h.
What it means
How tall is that gear?
Wheel diameters include a typical tire for each size. A fat tire adds an inch or so, which is about 3% on the gear.
Every unit
Your gear in every unit
Learn
Three things worth knowing
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Gear inches = wheel × chainring ÷ sprocket
A 50-tooth ring on a 17-tooth sprocket with a 26.3 in wheel gives 77 gear inches. Multiply by π/12 for development in feet.
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The penny-farthing measure
Before chains, the only way to get a taller gear was a bigger front wheel, up to 60 inches. When chains arrived, riders kept describing gears in the wheel size they replaced.
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Same sprockets, different gear
A 34/34 low gear is 26 gear inches on a road bike but 29 on a 29er. Compare gear inches or development, never the sprocket numbers alone.
Shortcuts
Popular gear conversions
Background
About bicycle gearing
Gear inches ask how large a direct-drive wheel would have to be to push the same as your gear: a hangover from penny-farthings that survived because it is easy to compare. Development asks the same question in plain distance: how far one turn of the pedals carries you.
Gain ratio is the modern answer, comparing wheel radius with crank length, so it accounts for the fact that long cranks make a gear easier.