Crank Length
There is a lot of discussion about “Short Cranks” now and we wanted to point out some of our reasoning for being a leader in this area. John Cobb was a very early adopter of using different length cranks from what the manufacturer supplied on the bike. Early on this was very difficult because of the industries lack of variable crank lengths but through commitment, he started having them manufactured and now you can access to this new fitting tool dynamic.
Aerodynamics: How Low is Too Low? This was one of the first reasons that we explored the shorter cranks. While developing faster rider positions in the wind tunnel, it was quickly apparent that many riders needed to get lower in the front but simply couldn’t because of upper thigh / stomach interference. Shortening the cranks led to some great breakthrough’s in aero positioning and continually needs to be explored by anyone doing serious TT work. To get the maximum aero benefits you have to go “all in” while testing and this absolutely means testing with shorter crank lengths. People spend hundreds of dollars to go to a wind tunnel to decide what helmet to use, that’s all nice but really you are wasting a lot of money if you don’t get your position maximized first. Ironman racing requires a different position than someone doing TT racing but there can be many, many minutes lost by being unnecessarily too high on the front of your bike and shorter cranks are often the key.
Performance Tuning: We did a crank drawing to show a very simple thing that can be very complicated to answer. When you change the crank arm length, what happens? Is there a power loss / gain? Do I save energy or spend energy? All of these are common questions. The basic answer is that your foot travels a shorter distance per pedal stroke and it is generally reported that there is no power loss or need to work harder because of the length change. There are several long, complex math equations that can be used to explore this but generally we find that the crank length is another great tool to use to help the rider go faster. It is a common experience that as a rider goes to shorter crank arm length for better aerodynamics, he/she will need to use a larger front chain ring to keep the muscle effort in a more familiar “feeling” range. Every muscle group has a range of contraction that is the most efficient and changing the mechanical work load points is a great way to keep the rider at the maximum point of efficiency and effort.
Toe Overlap: So many smaller riders experience Toe overlap, it’s scary and dangerous when your front wheel hit’s the end of your shoes while turning your bike. For almost any rider shorter than 5’1”, there will be toe interference with the front wheel, you don’t have to put up with this, going to a shorter 145, 150 or 155mm crank length will solve this and make your whole ridding experience much safer and better.
Hip / Knee Joint Replacement: Have you had a joint replacement? Do you have hip bone spurs that make cycling uncomfortable? Reducing the range of movement needs will really make your cycling more fun. Having the availability of shorter crank arm lengths gives the bike fitter a new tool to help the rider find more comfort, there will not be any “leverage” performance loss but there will be big gains in comfort.
Better Breathing: A common problem for many recreational riders is that their upper legs hit their stomach on every pedal stroke. If you happen to have a larger “spare tire” at the waist, this will be a common problem but even riders that are in great shape but have shorter legs will experience this interference. Interference with your breathing diaphragm is a major performance limiter and can be easily cured, there is no need to fall into the trap of having to ride in a bad position with your knees splayed out to find good comfort and performance.
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