Bicycle crank length
We think crank length is an under appreciated variable that can have a big impact on cycling performance. The reason for this is pretty well described in the following video.
If you can't or didn't see the video it goes into what some science says about crank length as it relates to performance and infers from there as to what this might mean for you. There are two major papers here. First is Determinants of maximal cycling power: crank length, pedaling rate and pedal speed by Martin and Spirduso of the University of Utah. While the paper concluded there was little lost riding 170 mm cranks they actually found that maximum power was actually achieved using 145 mm cranks, the difference being only abut 1%. The most relevant figure from that paper is reproduced below. . .
The second paper by McDaniel, et. al. entitled Determinants of metabolic cost during submaximal cycling looked at the effects of crank length and pedaling rate (cadence) on the metabolic cost of cycling. Again, crank length had almost no effect.
If crank length doesn't affect power production very much, why bother about crank length, why not just ride what came with your bike? Well, one problem with these studies is they didn't look at this relationship when the rider was in the aerodynamic position. Most experts agree that the lower one brings the front in trying to get into a good aerodynamic position the more the power is going to drop because of the difficulty in getting the thigh close to the chest. We would expect that this "crank length does not affect power" finding would not be so clear if position on the bicycle were added to the mix. But, even more important is the effect of crank length on aerodynamics. Simply shortening the crank and moving the seat up the same amount (and doing nothing else to the bike) does three things in this regard.
1. It moves the butt up in relationship to the shoulders so it flattens the back, generally regarded to be a better aerodynamic shape.
2. A shorter crank and reduces the frontal area, important to good aerodynamics, and,
3. It opens the distance between the knee and the chest at TDC, making it easier to get the crank up and making it possible to, possibly, lower the handlebars even more, again reducing the frontal area and flattening the back, improving aerodynamics.
Two anecdotal reports to illustrate the effects of this. One fitter was able to lower the front of a cyclist 7 cm by changing the crank length from 175 to 145. Despite this lowering he still was seeing a drop in his HR while riding at the same power. And, an article in Triathlete Magazine in 2008 on this subject reported that John Cobb reported reductions in drag, determined in a wind tunnel, from simply shortening the crank length and lowering the front appropriately, of 30%.
At PowerCranks we believe this will be very important to most riders in the future. Therefore, all PowerCranks now come with the ability to adjust crank length to almost any length you might want. Our basic cranks will now adjust from 145 mm to 182.5 mm and our long-adjustable cranks will adjust from 85 mm to 220 mm. Every PowerCranker will now be able to easily experiment with this to see what works best for them.