Ask three cyclists about the same gear and you may hear three numbers: ‘that’s a 3.1 ratio’, ‘about 84 inches’, ‘roughly six and a half metres of development’. They are all describing one thing — how far the bike goes for one turn of the pedals, relative to the wheel — in dialects invented in different centuries. This article translates between them, explains the penny-farthing ghost inside the inches figure, and tells you which dialect deserves your attention for climbing, cruising and comparing bikes.
A historical grace note: gear inches survived because they solve a real problem — they were the first unit in cycling that let a rider specify a gear without reference to a particular machine. Development is catching up as the practical unit precisely because modern riders care about their actual wheel, in a way the penny-farthing generation, whose wheel was the gear, never had to.
The ratio: the pure description
Gear ratio is chainring teeth divided by sprocket teeth. A 50-tooth ring driving a 16-tooth sprocket gives 3.125: the rear wheel turns 3.125 times per crank turn. The ratio says everything about the mechanism and nothing about the wheel wearing it — which is its limitation. Bolt the same gearing to a child’s small wheel and a 29er and the ratio is identical while the riding experience is completely different. Ratio is the engineer’s number: exact, clean, incomplete.
Key takeaways
- Ratio = chainring ÷ sprocket
- Development = ratio × wheel circumference
- Gear inches = ratio × wheel diameter in inches
Gear inches: the ghost of the penny-farthing
Before chain drives, a bicycle’s gearing was its front wheel: pedal a bigger wheel, travel further per turn. When chains arrived, riders needed a way to compare the new machines with the ordinaries they knew, so they expressed any gear as the diameter of the direct-drive wheel it equalled — ratio times wheel diameter, in inches. A century later the unit refuses to die, because it lets riders compare across wheel sizes and eras in one number. Climbing gears live near 20–30 inches; a road cruising gear near 70–90; a sprint or downhill gear beyond 120. When an old hand says ‘I need a 25-inch bottom gear for the Alps’, this is the language being spoken, and our gear calculator translates it into modern terms instantly.
Development: the ground truth
Development — metres travelled per crank revolution — is ratio times the actual circumference of your actual wheel and tyre. It is the only one of the three that knows about your tyre choice, and the only one that directly answers ‘how far do I go per pedal turn?’ It also exposes what changing tyres does: fitting a fatter tyre grows the wheel, quietly raising every gear by a percent or two. Multiply development by cadence and the chain of this site’s cycling maths completes itself: you get speed, which is the only number the road ever asked about.
| Combination | Ratio | Gear inches | Development |
|---|---|---|---|
| 34 × 28 (climbing) | 1.21 | 33″ | 2.55 m |
| 50 × 16 (cruising) | 3.13 | 84″ | 6.58 m |
| 52 × 11 (sprint) | 4.73 | 127″ | 9.95 m |
Singlespeed and fixed: where the languages earn their keep
Choose one gear for everything and the three descriptions become survival tools. Singlespeed and fixed-gear riders live or die by their single number — commonly in the 65–75 inch range for city riding, a compromise that can be spun on the flat and survived on the hills their city actually contains. Too high and every hill is a walk; too low and the flat becomes a hamster wheel. The check is this site’s gear calculator used honestly: the chosen gear’s speed at 90 rpm is your cruising speed, and at 60 rpm on your steepest street is your climbing reality. Both numbers must be livable, because there is no other gear coming to help.
The same logic, with more gears available, is what derailleur riders outsource to habit — which is why singlespeed riders, forced to think, often understand gearing best.
Internal hubs and belt drives: same maths, different furniture
Hub gears hide the ratio inside the hub — manufacturers publish it as a percentage range — but the outside of the system obeys the same arithmetic: an external chainring and sprocket set the primary ratio, the hub multiplies it, and development and gear inches follow identically. Belt drives change the sprocket materials, not the mathematics. If you are comparing a hub-geared city bike with a derailleur tourer, translate both into gear inches — it is the only common currency that makes the comparison honest, and it will often reveal that the ‘limited’ hub bike has the more sensible range for its job.
Electric assistance adds a motor, not an exemption: the gearing still decides what your legs must do at any speed, which is why under-geared e-bikes feel frantic at cruise. The languages of gearing outlive every technology thrown at them, because they describe the rider’s side of the bargain.
The numbers on famous bikes
It helps to anchor the languages in machines with reputations. A Brompton folder’s gears span roughly 33 to 100 inches across its six speeds — a city range chosen for starts and hills at one end and canal paths at the other. A classic steel tourer might run 25 to 105. A modern road racing bike spans about 33 (for the mountains its owner actually visits) to 130. A track bike sits fixed near 90. Lay those beside your own — the gear calculator gives inches for any combination in seconds — and the pattern emerges: every honest bicycle is a range fitted to a terrain and a rider, and the marketing number is only ever the top of it.
Notice, too, what the famous ranges share: the bottom gear is chosen by the worst hill the bike is truly expected to climb, and the rest of the range is arranged beneath a cruise gear the owner will live in. Specify a bicycle that way round — survival first, vanity last — and the three languages stop being trivia and become the spec sheet.
Choosing a lowest gear that exists in reality
The three languages converge on one practical task: verifying your easiest gear before terrain tests it. Take your lowest combination, compute its speed at the cadence you can hold on a long climb — 70 rpm is an honest figure for most — and ask whether you can balance and breathe at that speed on your steepest expected gradient. If the answer needs a 55 rpm grind, the cassette, not your character, is the problem. Fix gearing in the workshop, where it is cheap.
Common mistakes
- Comparing ratios between bikes with different wheel sizes
- Forgetting that a tyre swap re-gears the whole bike slightly
- Specifying a dream lowest gear without checking the speed it produces at climbing cadence
Questions this raises
Velodrome gearing runs high because speeds are high and there are no hills; 90–100 inches is a normal racing choice there.
Yes in the sense of distance per pedal turn — but hardness on a climb is about the speed that gear forces at your sustainable cadence. Context decides.
Put a number on it.
One gear, three descriptions, a century of arguments. Translating between ratio, gear inches and metres of development — and which to use for what.
Open the Gear & Cadence Calculator