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Wednesday, February 10, 2016

Crank Length for Track Cycling

There is a big misconception that shorter cranks provide superior acceleration compared to longer cranks, and this is mainly because short cranks are often associated with the explosive and strong track cyclist.  In reality, the reason why track cyclists have to lift weights and work on explosive training is solely to compensate for the baggage short cranks come with- an increased force required to produce the torque needed to move a smaller lever arm.

WHAT HAPPENS WHEN THE CRANK IS TOO SHORT OR TOO LONG?
It's reasonable to think shorter is better, especially when you consider that since the gears are fixed, faster speeds can only be reached by hitting a higher cadence.  But how do you know when the crank is too short?

When the cranks are too short, it will be too difficult to turn the cranks because your body simply can't generate the force needed to create torque.  As a result, it will take longer to climb up the rpm's- your accelerations will be slower, especially from a low speed.  Once you're at speed, you'll also find it impossible to get off the saddle because the cadence is too fast to maintain standing.  You'll also experience more muscle burn as a result of the legs moving too fast for effective circulation to take place.  If the blood doesn't have enough time to pick up the metabolic waste, accumulation will occur.  When the legs move too fast, this also creates a high pressure area that restricts blood flow and contributes to more lactic accumulation.

Going too long is a big problem mainly because although you'll have the fastest jump off the line, your top speed will be too low to be competitive.  Remember that as crank length increases, max cadence decreases.  When the crank is too long, your top speed will be at a very slow and exhausting cadence.  Accelerating the fastest is counterproductive if your top speed is so low that you'll always get passed right before the finish line!

THE OPTIMAL CRANK LENGTH FOR TRACK
The optimum crank length is the longest crank you can spin at the highest useable rpm.  If your fitness limits you to 35mph, pick the longest crank that peaks out at a cadence that represents this speed.  This gives the best of both worlds in a fixed gear situation, sacrificing the least amount of acceleration for the highest top speed.

Using a Pro as an example, Mark Cavendish uses a 170mm on his road bike and a 165mm on his track bike.  If the correct testing was done, the 165mm is the longest crank Cav can spin at the highest cadence.  Based on the gearing he prefers, going shorter will sacrifice too much acceleration and going longer will limit his top speed.

Interestingly, if you know your opponents' crank length, you'll be able to more accurately predict what strategy they'll gravitate towards.

Rider Strategy w/ Short Cranks:  Riders on shorter cranks will gravitate more towards attacking down the slope to avoid the torque issues.  After attacking, they'll try to spin as fast as possible and commit to whatever top speed they reach.  This rider will also be more likey to sprint much further away from the finish line, allowing enough time to reach the fastest top speed and make it impossible to come around and pass.

Rider Strategy w/ Long Cranks:  Riders on long cranks have the advantage if they cover most of the distance slowly to limit the sprint to a very small distance.  In order to expose the weakness of a rider on a shorter crank, attacking from a slow speed on the flatter sections or the lower sections of the corner will cause the opponent on the shorter crank to struggle.

If you're interested in optimizing your crank length for track racing, please contact me at EatSleepTrainSmart@gmail.com.