Intro to Gearing
















The bike you are currently riding, most likely, has 10 to 27 "speeds". Each rear cog represents a "speed". However, when you shift from one front chain-ring to another, you change the "speed" of the cogs. Thus, if you have five rear cogs and two front chain-rings, you have 10 different "speeds" to choose from - or do you?

The truth is that some of these combinations are, in effect, duplications. For example, a 15 tooth cog and a 42 tooth chain-ring have the identical impact of a 19 tooth cog and a 53 tooth chain-ring.

The only way to know how many "speeds" you really have is to convert each combination into something called chain inches. For every wheel size, there is a slightly different formula. I hate formulas, so rather than force you to learn how to use them; We have provided you with a spreadsheet that supplies the chain inches for the most commonly found combinations. With this chart, you can look at all the combinations at one glance. It is based upon a 700c wheel - which almost everyone uses. If you are riding a mountain bike, or a bike with unusual wheel dimensions, you will need to use the following formula:

The number of teeth in your front chain-ring, divided by the number of teeth in your rear cog, times the diameter of your wheel.

Once you have calculated the "speed" of each combination, you can decide if you wish to change some of your cogs, or chain-rings, to add new "speed" possibilities. Note, this is easier to do if you have a true Freewheel rather than a Cassette. Also, the maximum/minimum size of your cogs/chain-rings is determined by your derailers. We can also email you a FREE Excel spread sheet that you can use to test possiblechanges in your cog/chain-ring combinations. You will find a sample of it here.

 

 

Chain-ring
Cog 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53
11 94.0 96.4 98.8 101.2 103.6 106.0 108.4 110.8 115.4 117.8 120.3 122.7 125.2 127.6 130.1
12 86.1 88.3 90.5 92.8 95.0 97.2 99.4 101.6 105.8 108 110.2 112.5 114.8 117 119.3
13 79.5 81.5 83.6 85.6 87.7 89.7 91.7 93.8 97.6 99.7 101.8 103.8 105.9 108 110.1
14 73.8 75.7 77.6 79.5 81.4 83.3 85.2 87.1 90.6 92.6 94.5 96.4 98.4 100.3 102.2
15 68.9 70.7 72.4 74.2 76.0 77.7 79.5 81.3 84.6 86.4 88.2 90 91.8 93.6 95.4
16 64.6 66.3 67.9 69.6 71.2 72.9 74.5 76.2 79.3 81 82.7 84.4 86.1 87.8 89.4
17 60.8 62.4 63.9 65.5 67.0 68.6 70.1 71.7 74.6 76.2 77.8 79.4 81 82.6 84.2
18 57.4 58.9 60.4 61.8 63.3 64.8 66.3 67.7 70.5 72 73.5 75 76.5 78 79.5
19 54.4 55.8 57.2 58.6 60.0 61.4 62.8 64.2 66.8 68.2 69.6 71.1 72.5 73.9 75.3
20 51.7 53.0 54.3 55.7 57.0 58.3 59.6 61.0 63.5 64.8 66.2 67.5 68.8 70.2 71.5
21 49.2 50.5 51.7 53.0 54.3 55.5 56.8 58.0 60.4 61.7 63 64.3 65.6 66.9 68.1
22 47.0 48.2 49.4 50.6 51.8 53.0 54.2 55.4 57.7 58.9 60.1 61.4 62.6 63.8 65
23 44.9 46.1 47.2 48.4 49.5 50.7 51.8 53.0 55.2 56.3 57.5 58.7 59.9 61 62.2
24 43.1 44.2 45.3 46.4 47.5 48.6 49.7 50.8 52.9 54 55.1 56.3 57.4 58.5 59.6
25 41.3 42.4 43.5 44.5 45.6 46.6 47.7 48.8 50.8 51.8 52.9 54 55.1 56.2 57.2
Cog 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53
 

Chain-ring