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  Last updated: 12/6/2009


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 a common cycling complaint that can occasionally be an indicator that your crank length is incorrect for you.

A few links that might be of interest:

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). Shorter crankarms allow for faster cadences and improve cornering clearance on velodromes and in criteriums. They also avoid the effect of long crank arms to close the hip angle and reduce power - a benefit for velodromes and time trials.

  3. An increase in crank length leads to an increase in the lever arm and the ability to more force. Longer crankarms have long been touted as superior for hard steady efforts such as hill climbing and mountain biking. But studies have shown that while they change torque, power is unchanged and they require the rider to pedal a larger circle.

  4. 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): Track riders generally choose crankarms up to 5 mm shorter and mountain bikers up to 5 mm longer than the above recommendations.

And for those of you wanting to delve further into the subject, here is a link to a beta test version of a Crank Calc Program being developed by Nigel Jones of Machinehead Software.

To reinforce the above, here is a question posed to "Coach Fred" at entitled "Do Long Crankarms Help Time Trialing?"

Question: I'm a 36 and a competitive triathlete, usually placing top-5 in my age group. I use 170-mm crankarms but have heard that for time trialing, longer is better. Is that true? -- Harold F.

Coach Fred Matheny Replies: There have been studies of crankarm length, but the results aren't consistent. Some show that longer cranks provide greater leverage for turning big gears. Some show that shorter cranks foster greater speed via a faster cadence. And some show that crank length is completely individual. So, longer crankarms aren't a panacea for time trialing. In fact, there are dangers associated with them. The added length makes your knees bend more at the top of pedal strokes and extend more at the bottom -- both of which can lead to biomechanical injuries if you jump from 170 mm to, say, 180 mm. Also, longer cranks reduce cadence -- and a brisk cadence is the key to good time trialing. All this said, many time trialists use crankarms 2.5 mm longer than those on their normal road bike. Because 2.5 mm (one-tenth of an inch) isn't much, it rarely causes an injury. But the jury is still out on whether that bit of extra length actually improves performance.

Questions on content or suggestions to improve this page are appreciated.

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