Cassette Gear Ratios Explained: Sprocket Range, Jumps, and the Math Behind Cadence

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Sprocket Range: The Outer Numbers

A cassette is described by its smallest and largest sprocket: 11-28, 11-32, 10-36, 10-51, and so on. The span between those numbers is what you actually feel while riding. An 11-28 has a 17-tooth span; a 10-51 has a 41-tooth span. The bigger the span, the more terrain the bike can handle — but also, inevitably, the bigger the gaps between adjacent sprockets.

There is no free lunch here. A wide-range cassette buys you a climbing gear, but it costs you fine control over cadence on the flat. A narrow-range cassette lets you hold an exact cadence on rolling terrain but leaves you undergeared on steep climbs. The choice is always a trade-off between range and resolution.

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How to Calculate a Gear Ratio

A gear ratio is simply the number of chainring teeth divided by the number of sprocket teeth. A 50-tooth chainring with an 11-tooth sprocket gives 50 / 11 = 4.55 — the rear wheel turns 4.55 times per pedal revolution. A 34-tooth chainring with a 32-tooth sprocket gives 1.06 — barely more than one wheel turn per pedal stroke, which is why it feels so light on a steep gradient.

Multiply the ratio by wheel circumference (about 2.1 metres for a 700x25 road tyre) to get the distance travelled per pedal stroke, and then by cadence to get speed. A 50x11 ratio at 100 rpm of cadence gives roughly 57 km/h. This is the arithmetic that links pedalling to forward motion, and it's why gear ratio matters more than raw sprocket size.

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Sprocket Jumps: Why Close Spacing Matters

Look at the sequence of sprockets on a typical road cassette: 11-12-13-14-15-17-19-21-24-28. The first five sprockets differ by one tooth each; the last five step by two to four. One-tooth jumps let a rider hold cadence within a narrow band while the terrain changes gradually; the bigger jumps at the low end accept that climbing cadence varies more and that a perfect ratio matters less when you're grinding uphill.

This is exactly why road racers run 11-25 or 11-28 cassettes even when their frames could accept an 11-32. The finer the jumps, the easier it is to find the exact cadence that matches a breakaway pull, a time-trial effort, or a climb at threshold. Wide-range cassettes feel agricultural by comparison.

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1x vs 2x: Range vs Resolution

A 1x drivetrain (single chainring, no front derailleur) needs the cassette to carry the entire gear range. A typical 1x setup might use a 10-42 or 10-51 cassette with a 38- or 42-tooth chainring. The total range is huge — often wider than many 2x systems — but because there's only one chainring, every gear step has to be larger to cover the same spread.

Two-by systems give you two ranges of finely stepped gears with a single chainring change in the middle. A 50/34 compact with an 11-32 cassette delivers 22 distinct ratios, many of them only one tooth apart. The trade is mechanical complexity: a front derailleur, two shifters, and more to maintain and adjust.

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Common Cassette Ranges