tech
The Single-Speed Gear Calculator
Gear inches, development, gain ratio, and speed at cadence: the gearing math that actually matters when you only have one gear to pick.
Sheldon Brown's gear calculator is the reference every serious gearing conversation eventually traces back to. It is also built for the problem most cyclists actually have: a cassette and a set of chainrings, dozens of possible combinations, and a table wide enough to compare all of them at once.
Single speed removes that problem on purpose. There is one chainring, one cog, one ratio. What's left to calculate is smaller, but it's not nothing: the same three or four numbers that describe any gear also describe yours, and they're worth understanding before you pick a chainring and cog by feel.
The numbers
Gear ratio is just chainring teeth divided by cog teeth. 32:20 reduces to 1.6, nothing else involved. It's the number most riders actually swap at the trailhead because it takes no math and no chart, but it's also the least useful one here: it says nothing about wheel size, so a 1.6 on a 29+ wheel and a 1.6 on a 26-inch wheel ride nothing alike.
Gear inches is the oldest of these measurements, dating back to
directly-driven wheels of a specific diameter. It's still the most common
shorthand riders trade at the trailhead: wheel diameter (inches) × (chainring teeth ÷ cog teeth).
Development is the same idea in different units: the actual distance the bike travels for one full pedal revolution, in meters. It's what gear inches is trying to approximate, without the historical baggage.
Gain ratio, popularized by Sheldon Brown himself as an improvement on gear inches, accounts for crank length. Two bikes with identical gear inches but different crank arms don't feel the same to pedal, and gain ratio corrects for that.
Speed at cadence is development multiplied out across a range of pedaling speeds, which is the number that actually matters on the trail: what speed does this ratio put you at when you're spinning it out, and what speed does it put you at when you're grinding up a climb.
The calculator
Plug in a chainring, a cog, and a wheel/tire size, and the rest follows.
- Gear ratio (chainring ÷ cog)
- 1.60
- Gear inches
- 46.2
- Development (distance per pedal revolution)
- 3.69 m
- Gain ratio
- 3.36
| Cadence | km/h | mph |
|---|---|---|
| 60 rpm | 13.3 | 8.3 |
| 70 rpm | 15.5 | 9.6 |
| 80 rpm | 17.7 | 11.0 |
| 90 rpm | 19.9 | 12.4 |
| 100 rpm | 22.1 | 13.8 |
| 110 rpm | 24.4 | 15.1 |
Reading the output
None of these numbers tell you the "right" gear. That's still terrain, fitness, and stubbornness. What they're good for is comparison: deciding whether 32:20 on a 29+ wheel climbs like 30:18 on a standard 29er, or figuring out why a borrowed bike with the same chainring and cog as yours feels completely different once you notice it's running smaller wheels.
- gearing
- single-speed
- reference