Gear ratio, gear inches, development and gain ratio
A bicycle gear is two sprockets and a wheel. The gear ratio compares the sprockets: chainring teeth ÷ cog teeth. A ratio of three means the rear wheel turns three times for every turn of the pedals.
The ratio alone does not say how far the bike goes, because wheels differ. Three more measures put the wheel in. Gear inches = wheel diameter in inches × ratio. The figure is the diameter of the directly driven high wheel that would feel the same, which is where the measure comes from. Meters of development = wheel circumference × ratio: the distance covered by one turn of the pedals. Gear inches × 0.0254 × π gives development in meters.
The gain ratio, proposed by Sheldon Brown, also counts the crank: (wheel radius ÷ crank length) × ratio. It is a pure number, the distance the bike moves for each unit of distance the pedal travels around its circle, so it is the same in any unit, and it shows what a shorter or longer crank does to the effort.
All three need the size of the wheel with its tire. The calculator takes it from the marking on the sidewall: wheel diameter = rim bead seat diameter + 2 × tire width. Real tires are a little off their marking and flatten under load, so treat the last digit of any gear figure as approximate.
As a guide to the charts, one encyclopedia entry puts adult single speed bikes between fifty-five and seventy-five gear inches, and Sheldon Brown puts the lowest gear of most mountain bikes at around twenty-two to twenty-six.
Bicycle gear ratio chart: gear inches by cog and chainring
Each cell is the gear in gear inches for the cog in its row and the chainring in its column. Wheel = a 28-622 tire (700 × 28C).
| Chainring teeth | |||||||
|---|---|---|---|---|---|---|---|
| Cog teeth | 34 | 36 | 39 | 46 | 50 | 52 | 53 |
| 11 | 82.5 in | 87.4 in | 94.6 in | 111.6 in | 121.3 in | 126.2 in | 128.6 in |
| 12 | 75.6 in | 80.1 in | 86.8 in | 102.3 in | 111.2 in | 115.7 in | 117.9 in |
| 13 | 69.8 in | 73.9 in | 80.1 in | 94.5 in | 102.7 in | 106.8 in | 108.8 in |
| 14 | 64.8 in | 68.6 in | 74.4 in | 87.7 in | 95.3 in | 99.1 in | 101.1 in |
| 15 | 60.5 in | 64.1 in | 69.4 in | 81.9 in | 89.0 in | 92.5 in | 94.3 in |
| 16 | 56.7 in | 60.1 in | 65.1 in | 76.7 in | 83.4 in | 86.8 in | 88.4 in |
| 17 | 53.4 in | 56.5 in | 61.2 in | 72.2 in | 78.5 in | 81.6 in | 83.2 in |
| 19 | 47.8 in | 50.6 in | 54.8 in | 64.6 in | 70.2 in | 73.1 in | 74.5 in |
| 21 | 43.2 in | 45.8 in | 49.6 in | 58.5 in | 63.6 in | 66.1 in | 67.4 in |
| 23 | 39.5 in | 41.8 in | 45.3 in | 53.4 in | 58.0 in | 60.3 in | 61.5 in |
| 25 | 36.3 in | 38.4 in | 41.6 in | 49.1 in | 53.4 in | 55.5 in | 56.6 in |
| 28 | 32.4 in | 34.3 in | 37.2 in | 43.9 in | 47.7 in | 49.6 in | 50.5 in |
| 30 | 30.3 in | 32.0 in | 34.7 in | 40.9 in | 44.5 in | 46.3 in | 47.2 in |
| 32 | 28.4 in | 30.0 in | 32.5 in | 38.4 in | 41.7 in | 43.4 in | 44.2 in |
| 34 | 26.7 in | 28.3 in | 30.6 in | 36.1 in | 39.3 in | 40.8 in | 41.6 in |
Chart: meters of development by cog and chainring
Each cell is the distance the bike moves for one pedal turn, for the cog in its row and the chainring in its column. Wheel = a 28-622 tire (700 × 28C).
| Chainring teeth | |||||||
|---|---|---|---|---|---|---|---|
| Cog teeth | 34 | 36 | 39 | 46 | 50 | 52 | 53 |
| 11 | 6.58 m | 6.97 m | 7.55 m | 8.91 m | 9.68 m | 10.07 m | 10.26 m |
| 12 | 6.03 m | 6.39 m | 6.92 m | 8.16 m | 8.87 m | 9.23 m | 9.41 m |
| 13 | 5.57 m | 5.90 m | 6.39 m | 7.54 m | 8.19 m | 8.52 m | 8.68 m |
| 14 | 5.17 m | 5.48 m | 5.93 m | 7.00 m | 7.61 m | 7.91 m | 8.06 m |
| 15 | 4.83 m | 5.11 m | 5.54 m | 6.53 m | 7.10 m | 7.38 m | 7.53 m |
| 16 | 4.53 m | 4.79 m | 5.19 m | 6.12 m | 6.66 m | 6.92 m | 7.06 m |
| 17 | 4.26 m | 4.51 m | 4.89 m | 5.76 m | 6.26 m | 6.52 m | 6.64 m |
| 19 | 3.81 m | 4.04 m | 4.37 m | 5.16 m | 5.61 m | 5.83 m | 5.94 m |
| 21 | 3.45 m | 3.65 m | 3.96 m | 4.67 m | 5.07 m | 5.27 m | 5.38 m |
| 23 | 3.15 m | 3.33 m | 3.61 m | 4.26 m | 4.63 m | 4.82 m | 4.91 m |
| 25 | 2.90 m | 3.07 m | 3.32 m | 3.92 m | 4.26 m | 4.43 m | 4.52 m |
| 28 | 2.59 m | 2.74 m | 2.97 m | 3.50 m | 3.80 m | 3.96 m | 4.03 m |
| 30 | 2.41 m | 2.56 m | 2.77 m | 3.27 m | 3.55 m | 3.69 m | 3.76 m |
| 32 | 2.26 m | 2.40 m | 2.60 m | 3.06 m | 3.33 m | 3.46 m | 3.53 m |
| 34 | 2.13 m | 2.26 m | 2.44 m | 2.88 m | 3.13 m | 3.26 m | 3.32 m |
Single speed and fixed gear chart: gear inches by cog and chainring
The chainrings and cogs single speed and fixed gear bikes use. Wheel = a 32-622 tire (700 × 32C).
| Chainring teeth | ||||||
|---|---|---|---|---|---|---|
| Cog teeth | 38 | 40 | 42 | 44 | 46 | 48 |
| 13 | 78.9 in | 83.1 in | 87.3 in | 91.4 in | 95.6 in | 99.7 in |
| 14 | 73.3 in | 77.2 in | 81.0 in | 84.9 in | 88.7 in | 92.6 in |
| 15 | 68.4 in | 72.0 in | 75.6 in | 79.2 in | 82.8 in | 86.4 in |
| 16 | 64.1 in | 67.5 in | 70.9 in | 74.3 in | 77.6 in | 81.0 in |
| 17 | 60.4 in | 63.5 in | 66.7 in | 69.9 in | 73.1 in | 76.3 in |
| 18 | 57.0 in | 60.0 in | 63.0 in | 66.0 in | 69.0 in | 72.0 in |
| 19 | 54.0 in | 56.9 in | 59.7 in | 62.5 in | 65.4 in | 68.2 in |
| 20 | 51.3 in | 54.0 in | 56.7 in | 59.4 in | 62.1 in | 64.8 in |
| 22 | 46.6 in | 49.1 in | 51.6 in | 54.0 in | 56.5 in | 58.9 in |
Used by
- Bike gear ratio calculatorThe size of a bicycle gear in all four common measures.