CYCLING PERFORMANCE TIPS

Crank Length

Decisions on appropriate crank length are often steeped in mystique and considered part of the "art" of coaching for the competitive cyclists. Knee pain, especially chondromalacia, is often an indicator that your crank length is incorrect for you.

I did stumble across a nice review on the subject of picking your crank length. Other issues that have might be considered (you can make up your own mind on these) are:

  1. It has been recommended that competitive cyclists use shorter cranks than the normally recommended to reduce the dead spot at the top of the cycle, from 9 to 12 o'clock (viewed from the rider facing to the right) and to allow a shorter stroke through the strongest leg movement. This would avoid having the knee bed less than 90 deg.

  2. There is data showing that the shorter the crank, the higher the cadence that is possible (ultimately up to the rider). An increase in crank length leads to an increase in the lever arm and the ability to more force.

  3. Competitive cyclists ride comparatively smaller gears on the track in sprinting events (as opposed to the road) to allow optimal cadence in the shortest time. This is especially the case on banked tracks where the sprinter needs to changed direction suddenly at times. This facilitates reaching optimal cadence in the shortest time ( accelerating out of the bends). The same effect occurs with shorter cranks. The use of longer cranks allows for more leverage and so more power but can lead to a dead spot at the top of the stroke for those with a less than perfect pedal action & strength . In endurance events where the requirement for high cadence is not as great, the extra leverage is of benefit.
So if you feel more comfortable turning big gears at lower cadences, you'll like your crank arms a little longer. But if you prefer to spin at a higher cadence go with shorter crankarms.

If you change your crankarm length on your current set up, don't forget to adjust your seat height as changing crankarm length will change the distance from your seat to the lowest point of the crank cycle.

Here's a starting point for suggested crank lengths based on traditional wisdom - you can start here and then tailor them (up or down) to your own style and preferences:

Frame Size Crankarm Inseam Crankarm
54 cm or less 170 mm 80 cm or less 170 mm
55 - 58 cm 172.5 mm 81 - 86 cm 172.5 mm
59 cm or greater 175 mm 87 cm or above 175 mm
And from another source (referencing your inseam in inches):
And for those of you wanting to delve further into the subject, here is a link to a beta test version of a Cranc Calc Program being developed by Nigel Jones of Machinehead Software.

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