Gearing and Cadence
The Wattbike measures absolute mechanical power in Watts. The amount of power produced is measured from the sum of all the forces applied to the chain through the cranks. It is important to recognize that the underlying calculations for Speed (kph), pace (1/km) and distance per revolution are standard equations derived from Watts (W).
What is a Gear?
In addition to the measuring technology the basic construction of the Wattbike includes a chain, a 48 chainring and 13 sprocket combination. Fundamental to understanding how the Wattbike relates to cycling is the understanding of what chainrings and sprockets are and do, bike gearing and how the air brake gear lever, in particular can be used to simulate gearing on a bike. We have all heard about and probably used a gear on a bike – but what is a gear and what does it do? Simply a gear determines the distance a bike will travel in one complete pedal revolution. It is dependent on the circumference of the wheels and the size of the front ‘chainring’ and the back ‘sprocket’
The number of teeth on a chainring or sprocket determines its size. For instance a 52 chainring has 52 teeth; a 14 sprocket has 14 teeth. So you may hear a gear referred to as a 52/14. Chainrings commonly range from 39 teeth to 56 teeth in size (smaller and larger are available) and sprockets 11 teeth to 26 teeth – the combinations depend on the needs of the cyclist. Measuring the distance a bike travels over one complete pedal revolution is known as ‘rolling out’ and is measured in metres (known as ‘gear metres’). Put the bike into gear i.e. 52/14 roll the bike backwards for one complete pedal revolution. The distance between the start and finish position is measured.
Gear Metres can also be calculated from the equation:
Circumference of rear wheel = Diameter of rear wheel x π
Using a standard sprint rim with normal road tubular tyres a 52/14 gear is 7.93 m so in this gear combination the bike moves 7.93 m along the ground for every pedal revolution. Wheel diameter, tyre width and tyre pressure will alter the distance travelled per revolution. The higher the gear the further the bike will travel for one complete pedal revolution. In low gear the bike will not travel as far. A high gear is one which has a high teeth number on the chainring with a low teeth number on the sprocket. Conversely a low gear is one with a low teeth number on the chainring and high teeth number on the sprocket.
However there are many chainring and sprocket combinations available to achieve a particular gear metre. Tables showing gear metres and conversion to equivalent Wattbike settings are shown in Tables 1 and 2.
Table 1 - Standard Gear Metre Table (rolled out metres)
Standard Sprint Rim with normal road tubular tyre
| Sprocket Size | |||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | |
| 39 | 6.94 | 6.41 | 5.95 | 5.55 | 5.21 | 4.90 | 4.63 | 4.38 | 4.16 | 3.97 | 3.79 | 3.62 | 3.47 | 3.33 | 3.20 |
| 40 | 7.12 | 6.57 | 6.10 | 5.69 | 5.34 | 5.02 | 4.75 | 4.50 | 4.27 | 4.07 | 3.88 | 3.71 | 3.56 | 3.42 | 3.29 |
| 41 | 7.30 | 6.74 | 6.25 | 5.84 | 5.47 | 5.15 | 4.86 | 4.61 | 4.38 | 4.17 | 3.98 | 3.81 | 3.65 | 3.50 | 3.37 |
| 42 | 7.47 | 6.90 | 6.41 | 5.98 | 5.61 | 5.28 | 4.98 | 4.72 | 4.48 | 4.27 | 4.08 | 3.90 | 3.74 | 3.59 | 3.45 |
| 43 | 7.65 | 7.06 | 6.56 | 6.12 | 5.74 | 5.40 | 5.10 | 4.83 | 4.59 | 4.37 | 4.17 | 3.99 | 3.83 | 3.67 | 3.53 |
| 44 | 7.83 | 7.23 | 6.71 | 6.26 | 5.87 | 5.53 | 5.22 | 4.95 | 4.70 | 4.47 | 4.27 | 4.09 | 3.92 | 3.76 | 3.61 |
| 45 | 8.01 | 7.39 | 6.86 | 6.41 | 6.01 | 5.65 | 5.34 | 5.06 | 4.80 | 4.58 | 4.37 | 4.18 | 4.00 | 3.84 | 3.70 |
| 46 | 8.19 | 7.56 | 7.02 | 6.55 | 6.14 | 5.78 | 5.46 | 5.17 | 4.91 | 4.68 | 4.47 | 4.27 | 4.09 | 3.93 | 3.78 |
| 47 | 8.36 | 7.72 | 7.17 | 6.69 | 6.27 | 5.90 | 5.58 | 5.28 | 5.02 | 4.78 | 4.56 | 4.36 | 4.18 | 4.01 | 3.86 |
| 48 | 8.54 | 7.89 | 7.32 | 6.83 | 6.41 | 6.03 | 5.69 | 5.40 | 5.13 | 4.88 | 4.66 | 4.46 | 4.27 | 4.10 | 3.94 |
| 49 | 8.72 | 8.05 | 7.47 | 6.98 | 6.54 | 6.16 | 5.81 | 5.51 | 5.23 | 4.98 | 4.76 | 4.55 | 4.36 | 4.19 | 4.02 |
| 50 | 8.90 | 8.21 | 7.63 | 7.12 | 6.67 | 6.28 | 5.93 | 5.62 | 5.34 | 5.08 | 4.85 | 4.64 | 4.45 | 4.27 | 4.11 |
| 51 | 9.08 | 8.38 | 7.78 | 7.26 | 6.81 | 6.41 | 6.05 | 5.73 | 5.45 | 5.19 | 4.95 | 4.74 | 4.54 | 4.36 | 4.19 |
| 52 | 9.25 | 8.54 | 7.93 | 7.40 | 6.94 | 6.53 | 6.17 | 5.84 | 5.55 | 5.29 | 5.05 | 4.83 | 4.63 | 4.44 | 4.27 |
| 53 | 9.43 | 8.71 | 8.08 | 7.55 | 7.07 | 6.66 | 6.29 | 5.96 | 5.66 | 5.39 | 5.14 | 4.92 | 4.72 | 4.53 | 4.35 |
| 54 | 9.61 | 8.87 | 8.24 | 7.69 | 7.21 | 6.78 | 6.41 | 6.07 | 5.77 | 5.49 | 5.24 | 5.01 | 4.80 | 4.61 | 4.44 |
| 55 | 9.79 | 9.03 | 8.39 | 7.83 | 7.34 | 6.91 | 6.53 | 6.18 | 5.87 | 5.59 | 5.34 | 5.11 | 4.89 | 4.70 | 4.52 |
| 56 | 9.97 | 9.20 | 8.54 | 7.97 | 7.47 | 7.03 | 6.64 | 6.29 | 5.98 | 5.69 | 5.44 | 5.20 | 4.98 | 4.78 | 4.60 |
Table 2 - Standard Metric Gear Table
Approximate conversion to Wattbike Air Brake Gear Lever settings -Standard Sprint Rim with normal road tubular tyre
Black = Wattbike Pro, Red = Wattbike Trainer
| Sprocket Size | |||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | |
| 39 | 3/9 | 2/6 | 1/4 | 5.55/3 | 5.21/2 | 4.90/1 | 4.63 | 4.38 | 4.16 | 3.97 | 3.79 | 3.62 | 3.47 | 3.33 | 3.2 |
| 40 | 4/10 | 2/7 | 1/5 | 5.69/3 | 5.34/2 | 5.02/2 | 4.75 | 4.5 | 4.27 | 4.07 | 3.88 | 3.71 | 3.56 | 3.42 | 3.29 |
| 41 | 4 | 3/7 | 1/5 | 5.84/4 | 5.47/3 | 5.15/2 | 4.86 | 4.61 | 4.38 | 4.17 | 3.98 | 3.81 | 3.65 | 3.5 | 3.37 |
| 42 | 5 | 3/8 | 2/6 | 1/4 | 5.61/3 | 5.28/2 | 4.98/1 | 4.72 | 4.48 | 4.27 | 4.08 | 3.9 | 3.74 | 3.59 | 3.45 |
| 43 | 5 | 4/9 | 2/6 | 1/5 | 5.74/4 | 5.40/3 | 5.10/1 | 4.83 | 4.59 | 4.37 | 4.17 | 3.99 | 3.83 | 3.67 | 3.53 |
| 44 | 6 | 4/10 | 3/7 | 1/5 | 5.87/4 | 5.53/3 | 5.22/2 | 4.95/1 | 4.7 | 4.47 | 4.27 | 4.09 | 3.92 | 3.76 | 3.61 |
| 45 | 6 | 4 | 3/8 | 2/6 | 1/4 | 5.65/3 | 5.34/2 | 5.06/1 | 4.8 | 4.58 | 4.37 | 4.18 | 4 | 3.84 | 3.7 |
| 46 | 7 | 5 | 4/9 | 2/6 | 1/5 | 5.78/4 | 5.46/3 | 5.17/2 | 4.91/1 | 4.68 | 4.47 | 4.27 | 4.09 | 3.93 | 3.78 |
| 47 | 8 | 5 | 4/10 | 3/7 | 1/5 | 5.90/4 | 5.58/3 | 5.28/2 | 5.02/1 | 4.78 | 4.56 | 4.36 | 4.18 | 4.01 | 3.86 |
| 48 | 9 | 6 | 4 | 3/8 | 2/6 | 1/4 | 5.69/3 | 5.40/2 | 5.13/2 | 4.88 | 4.66 | 4.46 | 4.27 | 4.1 | 3.94 |
| 49 | 10 | 6 | 5 | 3/9 | 2/6 | 1/5 | 5.81/4 | 5.51/3 | 5.23/2 | 4.98/1 | 4.76 | 4.55 | 4.36 | 4.19 | 4.02 |
| 50 | 10 | 7 | 5 | 4/10 | 3/7 | 1/5 | 1/4 | 5.62/3 | 5.34/2 | 5.08/1 | 4.85 | 4.64 | 4.45 | 4.27 | 4.11 |
| 51 | 9.08 | 8 | 5 | 4/10 | 3/8 | 2/6 | 1/5 | 5.73/4 | 5.45/3 | 5.19/2 | 4.95/1 | 4.74 | 4.54 | 4.36 | 4.19 |
| 52 | 9.25 | 9 | 6 | 4 | 3/8 | 2/6 | 1/5 | 5.84/4 | 5.55/3 | 5.29/2 | 5.05/1 | 4.83 | 4.63 | 4.44 | 4.27 |
| 53 | 9.43 | 10 | 6 | 5 | 4/9 | 3/7 | 1/5 | 1/4 | 5.66/3 | 5.39/2 | 5.14/2 | 4.92/1 | 4.72 | 4.53 | 4.35 |
| 54 | 9.61 | 10 | 7 | 5 | 4/10 | 3/7 | 2/6 | 1/5 | 5.77/4 | 5.49/3 | 5.24/2 | 5.01/1 | 4.8 | 4.61 | 4.44 |
| 55 | 9.79 | 9.03 | 8 | 6 | 4 | 3/8 | 2/6 | 1/5 | 5.87/4 | 5.59/3 | 5.34/2 | 5.11/2 | 4.89 | 4.7 | 4.52 |
| 56 | 9.97 | 9.2 | 9 | 6 | 5 | 4/9 | 3/7 | 1/5 | 1/4 | 5.69/3 | 5.44/3 | 5.20/2 | 4.98/1 | 4.78 | 4.6 |
What are gear inches?
Gear inches is a system that assigns numerical measurements to gear ratios to indicate how low or high a gear is. It has no physical significance. Gear inches relate to the diameter in inches of the main wheel of an old-fashioned penny-farthing with equivalent gearing. To convert from gear inches to gear metres divide by 0.08 (more exactly: 0.0798, or precisely: 0.0254π). So for example level 1 on the Wattbike is 6.2 metres (at 90 cadence see section 4) or 6.2/0.08 =77.5 inches. The difference between gear inches and gear metres is the factor π i.e multiply by 3.142 to get the distance travelled in one pedal revolution.
6.2 / 0.08 = 77.5 inches
Gear inches originate from the old-fashioned penny-farthing when crankarms were attached directly to the large drive wheel. One turn of the pedals moved the bicycle a distance equal to the circumference of the wheel.
The larger the wheel the farther the bicycle went for each turn of the pedals. The gear-inch system is a holdover from these early days when wheel diameter determined the bike’s gearing. Riding in a high gear on a modern bike is mechanically equivalent to riding a penny-farthing with a large wheel whereas a low gear on a modern bike is the equivalent of a smaller wheel on a penny-farthing. Gear inches express gear ratios as the diameter of a directly-driven wheel and is calculated as follows: Diameter of drive wheel in inches × number of teeth on the chainring / number of teeth on the sprocket. The gear inches table is based on a wheel diameter of 27 inches. This means that a 48 teeth chainring/18 teeth sprocket setup is usually considered to be 72 inches. The full gear inches and conversion to equivalent Wattbike settings are shown in Tables 3 and 4.
Table 3- Imperial Gear Table
| Sprocket Size | |||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | |
| 39 | 87.8 | 81.0 | 75.2 | 70.2 | 65.8 | 62.0 | 58.5 | 55.4 | 52.7 | 50.2 | 47.9 | 45.8 | 43.9 | 42.1 | 40.5 |
| 40 | 90.0 | 83.1 | 77.2 | 72.0 | 67.5 | 63.5 | 60.0 | 56.9 | 54.0 | 51.4 | 49.1 | 47.0 | 45.0 | 43.2 | 41.5 |
| 41 | 92.3 | 85.2 | 79.1 | 73.8 | 69.2 | 65.1 | 61.5 | 58.3 | 55.4 | 52.7 | 50.3 | 48.1 | 46.1 | 44.3 | 42.6 |
| 42 | 94.5 | 87.2 | 81.0 | 75.6 | 70.9 | 66.7 | 63.0 | 59.7 | 56.7 | 54.0 | 51.6 | 49.3 | 47.3 | 45.4 | 43.6 |
| 43 | 96.8 | 89.3 | 82.9 | 77.4 | 72.6 | 68.3 | 64.5 | 61.1 | 58.1 | 55.3 | 52.8 | 50.5 | 48.4 | 46.4 | 44.7 |
| 44 | 99.0 | 91.4 | 84.9 | 79.2 | 74.3 | 69.9 | 66.0 | 62.5 | 59.4 | 56.6 | 54.0 | 51.7 | 49.5 | 47.5 | 45.7 |
| 45 | 101.3 | 93.5 | 86.8 | 81.0 | 76.0 | 71.5 | 67.5 | 64.0 | 60.8 | 57.9 | 55.2 | 52.8 | 50.6 | 48.6 | 46.7 |
| 46 | 103.5 | 95.6 | 88.7 | 82.8 | 77.6 | 73.1 | 69.0 | 65.4 | 62.1 | 59.2 | 56.5 | 54.0 | 51.8 | 49.7 | 47.8 |
| 47 | 105.8 | 97.6 | 90.7 | 84.6 | 79.3 | 74.7 | 70.5 | 66.8 | 63.5 | 60.4 | 57.7 | 55.2 | 52.9 | 50.8 | 48.8 |
| 48 | 108.0 | 99.7 | 92.6 | 86.4 | 81.0 | 76.3 | 72.0 | 68.2 | 64.8 | 61.7 | 58.9 | 56.4 | 54.0 | 51.9 | 49.9 |
| 49 | 110.3 | 101.8 | 94.5 | 88.2 | 82.7 | 77.8 | 73.5 | 69.6 | 66.2 | 63.0 | 60.1 | 57.5 | 55.1 | 52.9 | 50.9 |
| 50 | 112.5 | 103.9 | 96.4 | 90.0 | 84.4 | 79.4 | 75.0 | 71.1 | 67.5 | 64.3 | 61.4 | 58.7 | 56.3 | 54.0 | 51.9 |
| 51 | 114.8 | 105.9 | 98.4 | 91.8 | 86.1 | 81.0 | 76.5 | 72.5 | 68.9 | 65.6 | 62.6 | 59.9 | 57.4 | 55.1 | 53.0 |
| 52 | 117.0 | 108.0 | 100.3 | 93.6 | 87.8 | 82.6 | 78.0 | 73.9 | 70.2 | 66.9 | 63.8 | 61.1 | 58.5 | 56.2 | 54.0 |
| 53 | 119.3 | 110.1 | 102.2 | 95.4 | 89.5 | 84.2 | 79.5 | 75.3 | 71.6 | 68.2 | 65.1 | 62.2 | 59.6 | 57.3 | 55.0 |
| 54 | 121.5 | 112.2 | 104.2 | 97.2 | 91.1 | 85.8 | 81.0 | 76.8 | 72.9 | 69.4 | 66.3 | 63.4 | 60.8 | 58.3 | 56.1 |
| 55 | 123.8 | 114.3 | 106.1 | 99.0 | 92.8 | 87.4 | 82.5 | 78.2 | 74.3 | 70.7 | 67.5 | 64.6 | 61.9 | 59.4 | 57.1 |
| 56 | 126.0 | 116.3 | 108.0 | 100.8 | 94.5 | 89.0 | 84.0 | 79.6 | 75.6 | 72.0 | 68.7 | 65.8 | 63.0 | 60.5 | 58.2 |
Table 4 - Imperial Gear Table
Approximate conversion to Wattbike Air Brake Gear Lever settings
Black = Wattbike Pro, Red = Wattbike Trainer
| Sprocket Size | |||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | |
| 39 | 3/9 | 2/6 | 1/4 | 70.2/3 | 68.8/2 | 62.0/1 | 58.5 | 55.4 | 52.7 | 50.2 | 47.9 | 45.8 | 43.9 | 42.1 | 40.5 |
| 40 | 4/10 | 2/7 | 1/5 | 72.0/3 | 67.5/2 | 63.5/1 | 60 | 56.9 | 54 | 51.4 | 49.1 | 47 | 45 | 43.2 | 41.5 |
| 41 | 4 | 3/7 | 1/5 | 73.8/4 | 69.2/2 | 65.1/2 | 61.5 | 58.3 | 55.4 | 52.7 | 50.3 | 48.1 | 46.1 | 44.3 | 42.6 |
| 42 | 5 | 3/8 | 2/6 | 1/4 | 70.9/3 | 66.7/2 | 63.0/1 | 59.7 | 56.7 | 54 | 51.6 | 49.3 | 47.3 | 45.4 | 43.6 |
| 43 | 5 | 4/9 | 2/6 | 1/5 | 72.6/4 | 68.3/3 | 64.5/1 | 61.1 | 58.1 | 55.3 | 52.8 | 50.5 | 48.4 | 46.4 | 44.7 |
| 44 | 6 | 4/10 | 3/7 | 1/5 | 74.3/4 | 69.9/3 | 66.0/2 | 62.5/1 | 59.4 | 56.6 | 54 | 51.7 | 49.5 | 47.5 | 45.7 |
| 45 | 6 | 4 | 3/8 | 2/6 | 1/4 | 71.5/3 | 67.5/2 | 64.0/1 | 60.8 | 57.9 | 55.2 | 52.8 | 50.6 | 48.6 | 46.7 |
| 46 | 7 | 5 | 4/9 | 2/6 | 1/5 | 73.1/4 | 69.0/3 | 65.4/2 | 62.1/1 | 59.2 | 56.5 | 54 | 51.8 | 49.7 | 47.8 |
| 47 | 8 | 5 | 4/10 | 3/7 | 1/5 | 74.7/4 | 70.5/3 | 66.8/2 | 63.5/1 | 60.4 | 57.7 | 55.2 | 52.9 | 50.8 | 48.8 |
| 48 | 9 | 6 | 4 | 3/8 | 2/6 | 1/4 | 72.0/3 | 68.2/2 | 64.8/2 | 61.7 | 58.9 | 56.4 | 54 | 51.9 | 49.9 |
| 49 | 10 | 6 | 5 | 3/9 | 2/6 | 1/5 | 73.5/4 | 69.6/3 | 66.2/2 | 63.0/1 | 60.1 | 57.5 | 55.1 | 52.9 | 50.9 |
| 50 | 10 | 7 | 5 | 4/10 | 3/7 | 1/5 | 1/4 | 71.1/3 | 67.5/2 | 64.3/1 | 61.4 | 58.7 | 56.3 | 54 | 51.9 |
| 51 | 10 | 8 | 5 | 4/10 | 3/8 | 2/6 | 1/5 | 72.5/4 | 68.9/3 | 65.6/2 | 62.6/1 | 59.9 | 57.4 | 55.1 | 53 |
| 52 | 117 | 9 | 6 | 4 | 3/8 | 2/6 | 1/5 | 73.9/4 | 70.2/3 | 66.9/2 | 63.8/1 | 61.1 | 58.5 | 56.2 | 54 |
| 53 | 119.3 | 10 | 6 | 5 | 4/9 | 3/7 | 1/5 | 1/4 | 71.6/3 | 68.2/2 | 65.1/2 | 62.2/1 | 59.6 | 57.3 | 55 |
| 54 | 121.5 | 10 | 7 | 5 | 4/10 | 3/7 | 2/6 | 1/5 | 72.9/4 | 69.4/3 | 66.3/2 | 63.4/1 | 60.8 | 58.3 | 56.1 |
| 55 | 123.8 | 114.3 | 8 | 6 | 4 | 3/8 | 2/6 | 1/5 | 74.3/4 | 70.7/3 | 67.5/2 | 64.6/2 | 61.9 | 59.4 | 57.1 |
| 56 | 126 | 116.3 | 9 | 6 | 5 | 4/9 | 3/7 | 1/5 | 1/4 | 72.0/3 | 68.7/3 | 65.8/2 | 63.0/1 | 60.5 | 58.2 |