How to use
- 1Type your chainring teeth (e.g. 50,34) and cassette cogs (e.g. 11,12,…,28), or pick a preset.
- 2Choose your wheel and tyre size and enter your usual cadence.
- 3Pick what the table shows: speed, gear ratio, gear inches or development.
- 4Compare the hardest and easiest gear and the overall gear range.
Ratio, gear inches and development
Gear ratio is chainring teeth ÷ cog teeth: 50 × 11 is 4.55, 34 × 28 is 1.21. Development (or rollout) is how far one pedal turn moves you: ratio × wheel circumference, so 50 × 11 on a 700 × 25c tyre (2,105 mm) gives 9.57 m. Gear inches, the traditional English unit, is ratio × wheel diameter in inches — 50 × 11 is about 120 in, 34 × 28 about 32 in. Speed is development × cadence × 60, so 50 × 11 at 90 rpm is 51.7 km/h.
Wheel circumferences used
The tool uses common computer-setup values: 700 × 25c 2,105 mm, 700 × 28c 2,136 mm, 700 × 32c 2,155 mm, 29″ × 2.2 2,298 mm, 27.5″ × 2.25 2,182 mm and 26″ × 2.1 2,068 mm. The exact figure varies with rim width, tyre brand and pressure, so a measured roll-out on your own bike is the most accurate.
Choosing gearing for climbs
The gear range — hardest ratio ÷ easiest ratio — tells you how wide a drivetrain is: 50/34 with 11–28 gives 374%, a 1× MTB with 32 and 10–51 gives 510%. For long climbs most riders want an easiest gear where they can keep 70+ rpm: with 34 × 32 on 700 × 25c that is about 75 rpm at 10 km/h, but only about 60 rpm if a steep ramp slows you to 8 km/h.
Frequently asked questions
How do I calculate gear ratio on a bike?
Divide the chainring teeth by the rear cog teeth. A 52 chainring with a 13 cog is 52 ÷ 13 = 4.0, so the wheel turns four times per pedal revolution.
What are gear inches?
Gear inches are the gear ratio multiplied by the wheel diameter in inches — the diameter of an old penny-farthing wheel with the same effort. Road gears range from about 30 (easy climbing) to 120 (fast descending).
How fast can I go in my top gear?
Multiply the development by cadence and 60. 50 × 11 on 700 × 25c gives 9.57 m × 90 rpm × 60 ≈ 51.7 km/h; at 110 rpm, about 63 km/h.
Is 50/34 or 52/36 better?
50/34 (compact) gives easier climbing gears, 52/36 (semi-compact) gives higher top speed and tighter steps for strong riders. With an 11–30 or 11–32 cassette the 52/36 still climbs well.
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