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).

The Wattbike is factory calibrated – the tables below show our factory test data for power output at cadences of 40 to 130 in 10 cadence bands at each air brake resistance setting 1 to 10 - these are 'ideal' as they are generated using a motor to make sure of constant cadenThe 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).

The Wattbike is factory calibrated – the tables below show our factory test data for power output at cadences of 40 to 130 in 10 cadence bands at each air brake resistance setting 1 to 10 - these are 'ideal' as they are generated using a motor to make sure of constant cadence and application of force each pedal revolution.

The tables show the actual Watts produced and the derived speed and pace.ce and application of force each pedal revolution.

The tables show the actual Watts produced and the derived speed and pace.

Approximate relationship of Power (Watts)/Speed (kmh)/Air Brake Gear Lever setting 1-5, Cadence Metres per revolution (Factory)

ABGL 1 2 3 4 5
r/m Watts Speed Pace Watts Speed Pace Watts Speed Pace Watts Speed Pace Watts Speed Pace
40 26 17.4 207 27 17.7 204 29 18.1 199 34 19.2 187 37 19.8 181
50 41 20.6 175 43 21.0 172 48 21.8 165 55 23.0 157 60 23.7 152
60 59 23.6 153 63 24.2 149 74 25.6 140 85 27.0 133 95 28.1 128
70 83 26.7 135 92 27.8 130 107 29.4 123 126 31.2 115 141 32.5 111
80 115 30.2 119 126 31.2 115 145 32.9 110 168 34.7 104 197 36.8 98
90 151 33.4 108 165 34.5 104 200 37.0 97 230 39.0 92 265 41.1 88
100 189 36.2 99 213 37.9 95 260 40.8 88 300 43.0 84 348 45.4 79
110 243 39.8 91 280 41.9 86 340 45.0 80 400 47.8 75 462 50.4 71
120 300 43.0 84 340 45.0 80 410 48.3 75 490 51.5 70 570 54.5 66
130 365 46.2 78 410 48.3 75 495 51.7 70 600 55.5 65 710 59.1 61

 

Approximate relationship of Power (Watts)/Speed (kmh)/Air Brake Gear Lever setting 6-10, Cadence Metres per revolution (Factory)

 

ABGL 6 7 8 9 10
r/m Watts Speed Pace Watts Speed Pace Watts Speed Pace Watts Speed Pace Watts Speed Pace
40 40 20.4 176 42 20.8 173 44 21.2 170 46 21.5 167 48 21.8 165
50 67 24.7 146 72 25.4 142 73 25.5 141 78 26.1 138 83 26.7 135
60 102 28.9 125 113 30 120 119 30.6 118 126 31.2 115 132 31.7 113
70 157 33.8 106 166 34.5 104 175 35.2 102 189 36.2 99 198 36.9 98
80 218 38.2 94 235 39.3 92 253 40.4 89 272 41.5 87 286 42.2 85
90 300 43 84 325 44.3 81 345 45.3 80 370 46.5 77 385 47.1 76
100 390 47.4 76 428 49 73 460 50.3 72 495 51.7 70 515 52.5 69
110 520 52.7 68 570 54.5 66 620 56.2 64 655 57.4 63 690 58.5 62
120 625 56.4 64 690 58.5 62 740 60 60 805 61.9 58 853 63.3 57
130 800 61.8 58 860 63.4 57 935 65.4 55 1005 67.2 54 1055 68.4 53

 


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:

Gear in metres = diameter of rear wheel in metres x 3.142 (to get the circumference of the wheel) x No. of teeth on chainring / No. of teeth on sprocket.

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

 
SPROCKET SIZE
 
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
39
3
2
1
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
4
2
1
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
4
3
1
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
5
3
2
1
5.61
5.28
4.98
4.72
4.48
4.27
4.08
3.90
3.74
3.59
3.45
43
5
4
2
1
5.74
5.40
5.10
4.83
4.59
4.37
4.17
3.99
3.83
3.67
3.53
44
6
4
3
1
5.87
5.53
5.22
4.95
4.70
4.47
4.27
4.09
3.92
3.76
3.61
45
6
4
3
2
1
5.65
5.34
5.06
4.80
4.58
4.37
4.18
4.00
3.84
3.70
46
7
5
4
2
1
5.78
5.46
5.17
4.91
4.68
4.47
4.27
4.09
3.93
3.78
47
8
5
4
3
1
5.90
5.58
5.28
5.02
4.78
4.56
4.36
4.18
4.01
3.86
48
9
6
4
3
2
1
5.69
5.40
5.13
4.88
4.66
4.46
4.27
4.10
3.94
49
10
6
5
3
2
1
5.81
5.51
5.23
4.98
4.76
4.55
4.36
4.19
4.02
50
10
7
5
4
3
1
1
5.62
5.34
5.08
4.85
4.64
4.45
4.27
4.11
51
9.08
8
5
4
3
2
1
5.73
5.45
5.19
4.95
4.74
4.54
4.36
4.19
52
9.25
9
6
4
3
2
1
5.84
5.55
5.29
5.05
4.83
4.63
4.44
4.27
53
9.43
10
6
5
4
3
1
1
5.66
5.39
5.14
4.92
4.72
4.53
4.35
54
9.61
10
7
5
4
3
2
1
5.77
5.49
5.24
5.01
4.80
4.61
4.44
55
9.79
9.03
8
6
4
3
2
1
5.87
5.59
5.34
5.11
4.89
4.70
4.52
56
9.97
9.20
9
6
5
4
3
1
1
5.69
5.44
5.20
4.98
4.78
4.60

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 ∏ i.e multiply by 3.142 to get the distance travelled in one pedal revolution.

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

 
 SPROCKET SIZE
 
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
39
3
2
1
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
4
2
1
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
4
3
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
5
3
2
1
70.9
66.7
63.0
59.7
56.7
54.0
51.6
49.3
47.3
45.4
43.6
43
5
4
2
1
72.6
68.3
64.5
61.1
58.1
55.3
52.8
50.5
48.4
46.4
44.7
44
6
4
3
1
74.3
69.9
66.0
62.5
59.4
56.6
54.0
51.7
49.5
47.5
45.7
45
6
4
3
2