Bicycle Gears: Gear Ratio, Development, and Speed From Cadence
October 29, 2026
On a bicycle, the gear ratio is the number of teeth on the front chainring divided by the number of teeth on the rear cog. A ratio above 1 means the wheel turns more than once per pedal revolution. Gear development (also called rollout) is the distance the bike moves per pedal revolution = ratio × wheel circumference.
A 50 × 17 gear has a ratio of 2.94. A typical 700c road wheel with a tire has a circumference of about 2.1 m, so development = 2.94 × 2.1 = 6.18 m per pedal revolution. Gear inches (common in the US and UK) = ratio × wheel diameter in inches (about 27 for 700c): 2.94 × 27 = 79.4.
Skip the math and get your answer instantly:
Open the Speed Converter →Speed From Cadence
Speed = development × cadence. At 90 revolutions per minute (rpm): 6.18 m × 90 = 556 m per minute, which is 33.4 km/h (20.7 mph). A climbing gear of 34 × 32 has a ratio of 1.06 and a development of 2.23 m. At 70 rpm: 156 m per minute, 9.4 km/h (5.8 mph). A big gear of 52 × 11 has a ratio of 4.73 and a development of 9.93 m; at 100 rpm that is 1,000 m per minute, or 59.6 km/h (37 mph), which is typically only reached when sprinting or descending.
| Gear (front x rear) | Ratio | Development (m) | Speed at 90 rpm |
|---|---|---|---|
| 34 x 32 (climbing) | 1.06 | 2.23 | 12.0 km/h (7.5 mph) |
| 39 x 21 | 1.86 | 3.90 | 21.1 km/h (13.1 mph) |
| 50 x 17 | 2.94 | 6.18 | 33.4 km/h (20.7 mph) |
| 52 x 11 | 4.73 | 9.93 | 53.6 km/h (33.3 mph) |
Choosing Gears
For hills, a low gear (ratio near 1) at a comfortable cadence of 70 to 80 rpm lets you climb without burning out. For flat roads, a ratio of 2.5 to 4 at 85 to 100 rpm gives speeds of 28 to 50 km/h. The step between gears should be about 8% to 15% so that the cadence changes smoothly. Mountain bikes use smaller front rings (such as 32 teeth) with a wide cassette (10 to 52 teeth). Compact cranksets (50/34) and wide-range cassettes are popular among recreational riders.
Chainline and Efficiency
Extreme gear combinations (big ring to biggest cog, or small ring to smallest) cause chain angle and wear. Use the middle of the range for the best efficiency. Single-speed or fixed-gear bikes need a compromise ratio, commonly 2.5 to 3 (for example, 46 × 17 = 2.7 gives a development of 5.7 m).
Wheel Size Adjustments
Wheel circumference depends on the tire: 26-inch mountain bike wheels are around 2.07 m, 29-inch around 2.3 m, and 700c with a 25 mm tire about 2.1 m. Measure by rolling the loaded bike one wheel revolution for the most accurate figure, and use it in your computer settings.
Frequently Asked Questions
How do I compute gear ratio?
Chainring teeth divided by cog teeth.
What is gear development?
The distance traveled per pedal revolution.
How do I find speed from cadence?
Development multiplied by cadence.
What cadence is typical?
About 80 to 100 rpm on flat roads.
How many gear inches is a 50 x 17 on 700c?
About 79.