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January 20, 2012

Gear Inch Chart

Gear Inches are used to give a numberical value to how a particular chainwheel/cog combination will feel. Classic BMX gearing evolved over the years to be 44/16,which has 55 gear inches. The most popular gear ratios are pretty close to a 55 inch, which just seems to feel best for most people. In the charts below, I’ve bolded the most common combo’s. The number is derived from a simple formula: (chainring size divided by cog size) multiplied by wheel size.

If you want to learn more about gear ratios, go read the late, great Sheldon Brown’s explanation here.

BMX 20″ Wheel

9
10
11
12
13
14
15
16
17
18
23
51.1
46
41.8
38.3
35.4
32.9
30.7
28.8
27.1
25.6
24
53.3
48
43.6
40
36.9
34.3
32
30
28.2
26.7
25
55.6
50
45.5
41.7
38.5
35.7
33.3
31.3
29.4
27.8
26
57.8
52
47.3
43.3
40
37.1
34.7
32.5
30.6
28.9
27
60
54
49.1
45
41.5
38.6
36
33.8
31.8
30
28
62.2
56
50.9
46.7
43.1
40
37.3
35
32.9
31.1
29
64.4
58
52.7
48.3
44.6
41.4
38.7
36.3
34.1
32.2
30
66.7
60
54.5
50
46.2
42.9
40
37.5
35.3
33.3
31
68.9
62
56.4
51.7
47.7
44.3
41.3
38.8
36.5
34.4
32
71.1
64
58.2
53.3
49.2
45.7
42.7
40
37.6
35.6
33
73.3
66
60
55
50.8
47.1
44
41.3
38.8
36.7
34
75.6
68
61.8
56.7
52.3
48.6
45.3
42.5
40
37.8
35
77.8
70
63.6
58.3
53.8
50
46.7
43.8
41.2
38.9
36
80
72
65.5
60
55.4
51.4
48
45
42.4
40
37
82.2
74
67.3
61.7
56.9
52.9
49.3
46.3
43.5
41.1
38
84.4
76
69.1
63.3
58.5
54.3
50.7
47.5
44.7
42.2
39
86.7
78
70.9
65
60
55.7
52
48.8
45.9
43.3
40
88.9
80
72.7
66.7
61.5
57.1
53.3
50
47.1
44.4
41
91.1
82
74.5
68.3
63.1
58.6
54.7
51.3
48.2
45.6
42
93.3
84
76.4
70
64.6
60
56
52.5
49.4
46.7
43
95.6
86
78.2
71.7
66.2
61.4
57.3
53.8
50.6
47.8
44
97.8
88
80
73.3
67.7
62.9
58.7
55
51.8
48.9
45
100
90
81.8
75
69.2
64.3
60
56.3
52.9
50
46
102.2
92
83.6
76.7
70.8
65.7
61.3
57.5
54.1
51.1
47
104.4
94
85.5
78.3
72.3
67.1
62.7
58.8
55.3
52.2
48
106.7
96
87.3
80
73.8
68.6
64
60
56.5
53.3
49
108.9
98
89.1
81.7
75.4
70.0
65.3
61.3
57.6
54.4

BMX 24″ Wheel

9
10
11
12
13
14
15
16
17
18
23
61.3
55.2
50.2
46
42.5
39.4
36.8
34.5
32.5
30.7
24
64
57.6
52.4
48
44.3
41.1
38.4
36
33.9
32
25
66.7
60
54.5
50
46.2
42.9
40
37.5
35.3
33.3
26
69.3
62.4
56.7
52
48
44.6
41.6
39
36.7
34.7
27
72
64.8
58.9
54
49.8
46.3
43.2
40.5
38.1
36
28
74.7
67.2
61.1
56
51.7
48
44.8
42
39.5
37.3
29
77.3
69.6
63.3
58
53.5
49.7
46.4
43.5
40.9
38.7
30
80
72
65.5
60
55.4
51.4
48
45
42.2
40
31
82.7
74.4
67.6
62
57.2
53.1
49.6
46.5
43.8
41.3
32
85.3
76.8
69.8
64
59.1
54.9
51.2
48
45.2
42.7
33
88
79.2
72
66
60.9
56.6
52.8
49.5
46.6
44
34
90.7
81.6
74.2
68
62.8
58.3
54.4
51
48
45.3
35
93.3
84
76.4
70
64.6
60
56
52.5
49.4
46.7
36
96
86.4
78.5
72
66.5
61.7
57.6
54
50.8
48
37
98.7
88.8
80.7
74
68.3
63.4
59.2
55.5
52.2
49.3
38
101.3
91.2
82.9
76
70.2
65.1
60.8
57
53.6
50.7
39
104
93.6
85.1
78
72
66.9
62.4
58.5
55.1
52
40
106.7
96
87.3
80
73.8
68.6
64
60
56.5
53.3
41
109.3
98.4
89.5
82
75.7
70.3
65.6
61.5
57.9
54.7
42
112
100.8
91.6
84
77.5
72
67.2
63
59.3
56
43
114.7
103.2
93.8
86
79.4
73.7
68.8
64.5
60.7
57.3
44
117.3
105.6
96
88
81.2
75.4
70.4
66
62.1
58.7
45
120
108
98.2
90
83.1
77.1
72
67.5
63.5
60
46
122.7
110.4
100.4
92
84.9
78.9
73.6
69
64.9
61.3
47
125.3
112.8
102.5
94
86.8
80.6
75.2
70.2
66.4
62.7
48
128
115.2
104.7
96
88.6
82.3
76.8
72
67.8
64
49
130.7
117.6
106.9
98
90.5
84
78.4
73.5
69.2
65.3

January 20, 2012

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