Getting Technical
Gears, where are they from?
In the UK, gear ratios were traditionally measured in inches; the number of inches being the diameter of a wheel which would travel a 
certain distance along the road for a complete revolution of the wheel. Obviously, the greater the diameter, the greater the circumference and hence the greater the distance travelled. It was a way of measuring the Mechanical Advantage (MA) that the bicycle gave you. Think of the MA as the multiplier between the distance your feet move for every turn of the pedals and the distance you travel along the road.
This was perfectly straightforward and obvious in the days of the Ordinary bicycle (the Penny-Farthing).
Gear Chart
| REAR COG |
|||||||||||||
| 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | ||
| 26 | 63.8 | 58.5 | 54.0 | 50.1 | 46.8 | 43.9 | 41.3 | 39.0 | 36.9 | 35.1 | 33.4 | 31.9 | |
| 27 | 66.3 | 60.8 | 56.1 | 52.1 | 48.6 | 45.6 | 42.9 | 40.5 | 38.4 | 36.5 | 34.7 | 33.1 | |
| 28 | 68.7 | 63.0 | 58.2 | 54.0 | 50.4 | 47.3 | 44.5 | 42.0 | 39.8 | 37.8 | 36.0 | 34.4 | |
| 29 | 71.2 | 65.3 | 60.2 | 55.9 | 52.2 | 48.9 | 46.1 | 43.5 | 41.2 | 39.2 | 37.3 | 35.6 | |
| 30 | 73.6 | 67.5 | 62.3 | 57.9 | 54.0 | 50.6 | 47.6 | 45.0 | 42.6 | 40.5 | 38.6 | 36.8 | |
| 31 | 76.1 | 69.8 | 64.4 | 59.8 | 55.8 | 52.3 | 49.2 | 46.5 | 44.1 | 41.9 | 39.9 | 38.0 | |
| 32 | 78.5 | 72.0 | 66.5 | 61.7 | 57.6 | 54.0 | 50.8 | 48.0 | 45.5 | 43.2 | 41.1 | 39.3 | |
| 33 | 81.0 | 74.3 | 68.5 | 63.6 | 59.4 | 55.7 | 52.4 | 49.5 | 46.9 | 44.6 | 42.4 | 40.5 | |
| 34 | 83.5 | 76.5 | 70.6 | 65.6 | 61.2 | 57.4 | 54.0 | 51.0 | 48.3 | 45.9 | 43.7 | 41.7 | |
| 35 | 85.9 | 78.8 | 72.7 | 67.5 | 63.0 | 59.1 | 55.6 | 52.5 | 49.7 | 47.3 | 45.0 | 43.0 | |
| 36 | 88.4 | 81.0 | 74.8 | 69.4 | 64.8 | 60.8 | 57.2 | 54.0 | 51.2 | 48.6 | 46.3 | 44.2 | |
| C | 37 | 90.8 | 83.3 | 76.8 | 71.4 | 66.6 | 62.4 | 58.8 | 55.5 | 52.6 | 50.0 | 47.6 | 45.4 |
| H | 38 | 93.3 | 85.5 | 78.9 | 73.3 | 68.4 | 64.1 | 60.4 | 57.0 | 54.0 | 51.3 | 48.9 | 46.6 |
| A | 39 | 95.7 | 87.8 | 81.0 | 75.2 | 70.2 | 65.8 | 61.9 | 58.5 | 55.4 | 52.7 | 50.1 | 47.9 |
| I | 40 | 98.2 | 90.0 | 83.1 | 77.1 | 72.0 | 67.5 | 63.5 | 60.0 | 56.8 | 54.0 | 51.4 | 49.1 |
| N | 41 | 100.6 | 92.3 | 85.2 | 79.1 | 73.8 | 69.2 | 65.1 | 61.5 | 58.3 | 55.4 | 52.7 | 50.3 |
| 42 | 103.1 | 94.5 | 87.2 | 81.0 | 75.6 | 70.9 | 66.7 | 63.0 | 59.7 | 56.7 | 54.0 | 51.5 | |
| R | 43 | 105.5 | 96.8 | 89.3 | 82.9 | 77.4 | 72.6 | 68.3 | 64.5 | 61.1 | 58.1 | 55.3 | 52.8 |
| I | 44 | 108.0 | 99.0 | 91.4 | 84.9 | 79.2 | 74.3 | 69.9 | 66.0 | 62.5 | 59.4 | 56.6 | 54.0 |
| N | 45 | 110.5 | 101.3 | 93.5 | 86.8 | 81.0 | 75.9 | 71.5 | 67.5 | 63.9 | 60.8 | 57.9 | 55.2 |
| G | 46 | 112.9 | 103.5 | 95.5 | 88.7 | 82.8 | 77.6 | 73.1 | 69.0 | 65.4 | 62.1 | 59.1 | 56.5 |
| 47 | 115.4 | 105.8 | 97.6 | 90.6 | 84.6 | 79.3 | 74.6 | 70.5 | 66.8 | 63.5 | 60.4 | 57.7 | |
| 48 | 117.8 | 108.0 | 99.7 | 92.6 | 86.4 | 81.0 | 76.2 | 72.0 | 68.2 | 64.8 | 61.7 | 58.9 | |
| 49 | 120.3 | 110.3 | 101.8 | 94.5 | 88.2 | 82.7 | 77.8 | 73.5 | 69.6 | 66.2 | 63.0 | 60.1 | |
| 50 | 122.7 | 112.5 | 103.8 | 96.4 | 90.0 | 84.4 | 79.4 | 75.0 | 71.1 | 67.5 | 64.3 | 61.4 | |
| 51 | 125.2 | 114.8 | 105.9 | 98.4 | 91.8 | 86.1 | 81.0 | 76.5 | 72.5 | 68.9 | 65.6 | 62.6 | |
| 52 | 127.6 | 117.0 | 108.0 | 100.3 | 93.6 | 87.8 | 82.6 | 78.0 | 73.9 | 70.2 | 66.9 | 63.8 | |
| 53 | 130.1 | 119.3 | 110.1 | 102.2 | 95.4 | 89.4 | 84.2 | 79.5 | 75.3 | 71.6 | 68.1 | 65.0 | |
| 54 | 132.5 | 121.5 | 112.2 | 104.1 | 97.2 | 91.1 | 85.8 | 81.0 | 76.7 | 72.9 | 69.4 | 66.3 | |
