Bike gear calculator

A cog with zero or negative teeth is not a valid sprocket, so those requests fail with invalid_input and are not billed.

What gear ratio and metres of development actually measure

The arithmetic is deterministic, uses the same module in the browser and on the API, and never consults a network, a clock, or a random generator.

Input contract, formula, and when the calculator rejects a request

Chainring teeth must be greater than zero and at most eighty, covering compact, standard, and most chain-guide rings. Wheel diameter is the outer diameter in metres including the tyre, not the ISO bead-seat diameter printed as six hundred twenty-two millimetres on a seven-hundred-c rim. Typical road values sit near zero point six seven to zero point six eight metres once the tyre is mounted; twenty-nine-inch mountain tyres are larger, folding and kids wheels are smaller. Diameter must fall between zero point two and one point five metres inclusive. Example: fifty chainring teeth, twelve cog teeth, and a wheel diameter of zero point six eight metres yields ratio four point one six seven and a little over eight point nine metres of development per crank revolution. POST a JSON body with three required finite numbers: chainring_teeth, cog_teeth, and wheel_diameter_m. Chainring teeth may also arrive as chainring, front_teeth, ring_teeth, or front_chainring; cog teeth accept cog, rear_teeth, sprocket, and cassette_teeth; diameter accepts wheel_diameter, diameter_m, diameter, and wheel_d. Cog teeth must be a positive number in the same band: zero or negative cog teeth is not a valid sprocket and fails with invalid_input naming cog_teeth, and those failures are not billed. Missing fields, empty strings, non-finite values, and out-of-range numbers fail with invalid_input naming the field. On success the body echoes the three inputs, then circumference_m equal to pi times diameter, ratio equal to chainring over cog, development_m equal to ratio times circumference, and a formula string restating the identity. Prefer development_m on cassette cards and shop pages; keep ratio when you want the unitless tooth ratio beside the distance.

Where a bike gear calculator earns its keep, and what it is not

Call the free in-browser bike gear calculator for workshop demos, bike-shop cassette comparisons, and club nights where riders want metres of development without opening a spreadsheet. Riders choosing gears for a steep climb or a fast descent can rank sprockets by metres per crank revolution instead of by tooth count alone. Use the prepaid API when a retailer configurator, coaching log, or fleet tool needs a stable contract under KIT balance at $0.002 per successful item; validation failures never consume balance after the engine rejects the request. Pair a measured outer diameter—or a tabulated diameter for the tyre you actually run—with each chainring and cog you are considering, store development_m beside the sprocket, and remember that sidewall markings such as seven hundred by twenty-five do not equal outer diameter until you add twice the tyre height to the bead-seat diameter. This landing does not convert cadence into kilometres per hour, does not compute industrial pinion-and-gear mesh ratios for shafts, and does not emit gear inches or gain ratios; those are different search intents with their own tools. Authors shipping SDKs can map ratio and development_m into comparison tables for compact versus standard chainsets, eleven-speed versus twelve-speed cassettes, and twenty-six-inch versus twenty-nine-inch wheels—the same numbers a mechanic computes by dividing teeth and multiplying by pi times diameter.