A4 scale = 70%
| | A4 scale = 70% |
Cycle transmission notes page 3 ... Cranks and chainsets continued
It is important to use the correct length of crank to ensure that your legs can work efficiently. You risk damaging your knees if you habitually use cranks which are too long, especially as you get older. 170mm cranks, which most cycle manufacturers fit as standard to most bicycles, are unsuitable for anyone shorter than the average European adult male and are therefore too long for most people in the World!
Normally fit adult riders should use cranks which measure about 20% of their effective leg length, rounded to the nearest 5mm, whereas growing children can safely increase this figure to 22%. This length goes all the way to your hip joint and cannot be measured directly. Ask a friend to measure your height twice - first when you are standing upright against a wall, without shoes on, and second when you are sitting squarely against it. Then subtract one measurement from the other one, as shown below.
The following table shows recommended crank lengths for normally fit riders on upright bicycles, based on the 20% to 22% range. Even shorter cranks may be required by disabled riders with restricted knee movement and by users of faired racing recumbents (due to space restrictions). Additionally, riders with very long legs may need shorter cranks on standard upright bicycles, to prevent their toes hitting the front wheel or their pedals hitting the ground when cornering.
Note that, not only do riders with shorter legs need shorter cranks, they also need smaller chainrings and will ride slower than riders with long legs and long cranks (rear cranks on tandems are an exception to this). Never try to achieve a higher gear ratio by using longer cranks.
 | leg : | 50 | 52.5 | 55 | 57.5 | 60 | 62.5 | 65 | 67.5 | 70 | 72.5 | 75 | 77.5 | 80 | 82.5 | 85 | 87.5 | 90 | 92.5 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
 | child : adult : | 110 100 | 115 105 | 120 110 | 125 115 | 130 120 | 140 125 | 145 130 | 150 135 | 155 140 | 160 145 | 160 150 | 165 155 | 170 160 | 175 165 | 175 170 | 180 175 | 180 180 | 185 185 |
Highpath can supply cranks of various lengths as well as crank shorteners. We can also shorten cranks for customers and make special cranks designed to solve disability problems, such as when different lengths are required for each leg. See Cranks and Pedals for more details.
A wide range of chainrings is available to fit 5-arm cranks with common pcds like 130, 110, 94, 74 and 58mm, from cheap-and-nasty steel ones to expensive ones made from aerospace materials. Several of the mid-price aluminium chainrings are more than adequate for general use but, if you want them to run true and last a long time, it makes sense to buy the best.
Most chainrings are only available with an even number of teeth up to about 50 teeth. EGGring custom chainrings, on the other hand, allow you to specify any size you want up to 110 teeth. They are available in various weights, finishes and shapes, and most importantly, their aerospace material and full tooth profile mean they last much longer than other aluminium chainrings. EGGrings are made for all cycles, including racers, mountain-bikes and tourers, and they have been used to win Olympic gold medals and have even been exhibitted in London's world-famous Science Museum.
There is often confusion about so-called '10 speed chainrings' - but there are no such things as all derailleur chainrings are suitable for all systems from 3 to 10 speed. However some '10 speed' cranks place their chainrings slightly closer together, but this isn't critical.
| © Chris Bell, 2006 | next page... |
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