It is true that many top athletes are switching to shorter cranks for timed racing such as triathlon and TT. This is a relatively new trend because longer cranks were traditionally thought to provide better leverage. However, crank length is just one lever in a drive train composed of a system that transmits your foot’s force on the pedal to your tire’s thrust on the ground. The other levers in this system are the chainring radius, cog radius, and wheel radius. We vary two of these (chainring and cog) at will whenever we shift gears. So a small difference in crank length doesn’t affect leverage.
Believe it or not, top industry tests showed no statistical difference in maximum power among the three middle crank lengths (145, 170 and 195mm). For years crank-length tests had been inconclusive, and the general working knowledge came more from experience and intuition than science. I remember when I first hit the Elite seen before Pro, at 5ft6 I was riding a 172.5 on my TT bike which looking back was crazy. Now athletes can choose the crank length they like without worrying about affecting power.
With maximum power essentially unaffected by a wide range of reasonable crank lengths, athletes are now free to choose crank length based on other criteria. Convenience (you might already have a serviceable crank on your bike); comfort; pedal clearance (from the ground); toe overlap — all of these are affected by crank length. However, what is now understood is that, especially in an aero riding position, shorter cranks can sometimes alleviate a common fit problem: If the hip angle is too tight at the top of the pedal stroke, the athlete can be uncomfortable or is unable to produce maximum power at the top of the pedal stroke. Even in athletes with no existing fit problem, some choose shorter cranks to drop the torso still further by lowering the arm pads.
Some athletes keep their long cranks and still perform well. Some try short cranks, aren’t happy with the results, and switch back again. So, at the end of all of this, it now becomes the desire of the athlete more than anything else. Correct fits, correct technique and understanding your power/stats are the keys to your riding success.
These days, if you don’t know that, you are at a disadvantage. Now, after all of that, there is a different answer to that question for the road cyclist, stage racer or endurance rider. Give us a call if you ever want to talk power and crank lengths and don’t forget to pop in and check us out. The pedal smoothness 3-day course is a must at a starting level to understand how to control torque without fatiguing.
Nick is a Pro Cyclist certified and endorsed by USA Cycling and Training Peaks as a coach and power based trainer. You can catch him at probikefc.com