Kinesiological Approach to Finding your Optimal Crank Length

Rather than using anthropometric methods to determine optimal crank length, I would like to propose an easier method that involves just a little bit of self awareness.  After spending nearly $1k just to experiment with a 165mm, 170mm and 172.5mm crank, crank length greatly affected my technique and even, post-ride recovery.  Just to note, I ran a 53/39 and 11/23 cassette for all three lengths.

165mm

At 165mm, I naturally gravitated towards higher RPM's.  Since I was often 100rpm or higher, I always felt glued to the saddle.  I could sustain more power during steady state efforts, experienced the lowest heart rate for the same power, and I experienced the smallest amount of DOMS at this length.  I could definitely ride my fastest century at this crank length, and feel great the next day.  However, the awesome steady state performance came at the expense of accelerations.  Since anything lower than 100rpm felt like slow, pedal smashing, I could not get any meaningful power out of the saddle at any gear, and had to resort to seated accelerations requiring me to spin from 100-130rpm, shift, then repeat- it felt extremely S L O W.  In order to prevent abrupt changes in cadence, I had to shift three times to maintain some sort of continuity.  In terms of power, my sprints were 600 watts lower at this crank length; it's an understatement to say that I felt crippled in the one and only crit I experimented this length with.  I was constantly gapped anytime the group would accelerate just a few mph, losing the slipstream and forcing me to time trial my way back to the group.  For time trials and long, steady rides, this is great, BUT avoid short crank arms if accelerations are necessary.  Although this could be a positive, it felt like I could never tap anywhere close to my maximal heart rate at this crank length.

172.5mm

At 172.5mm, my natural inclination was to ride standing, but it felt powerful and effortless; just like Alberto Contador during long climbs.  Since my cadence was often 80rpm or lower, pedaling in a seated position always felt like pedal smashing.  Forcing myself to ride at higher cadences led to an obvious loss of technique, efficiency and power.  In sprints, my power was around 600 watts higher at this longer crank length.  In crits, I could catch attacks and breakaway attempts with ease.  Although this sounds like the perfect crank length, the major downside was the extreme DOMS/ muscle fatigue post-ride, and the extremely high heart rate at steady state.  This length also made steady efforts extremely tiring and difficult.  The massive benefits in sprints and accelerations weren't worth turning into a glass cannon that would break under steady state efforts or multi-race days.  However, if I only had one race and nothing the next day, I would definitely use 172.5mm.

170mm

At 170mm, I never had any inclination to stay seated or standing.  My natural cadence ranged from 85-100rpm, so I felt efficient in standing or seated efforts.  My sprint power was a couple hundred watts lower, and my steady state power was only 10 watts lower for the same heart rate.  My heart rate response was significantly less exaggerated and did not remain uncomfortably high like it did at 172.5mm, but I was able to utilize all heart rate zones, so it felt like I could use my full potential if needed.  With regards to DOMS/ fatigue, I can recover much faster than the 172.5mm, but experienced moderately more fatigued than the 165mm.  This is the length that I used to achieve seven podiums out of eight races in one season.

WHAT'S YOUR OPTIMAL CRANK LENGTH?

It has been several years since I wrote this post, but wanted to update this because my experience at 172.5mm is now more like the 170mm crank.  What changed?  I dedicated A LOT of time on flexibility and mobility.  Longer crank lengths require more flexibility and mobility to push efficiently, and at the time of writing, I did not have the required ROM to push this crank efficiently.

CRANK LENGTH & PHYSICAL REQUIREMENTS

By now, you should have a good idea of whether or not your current crank is long, short or at the middle.  Depending on whether your crank is long or short, the focus of your training will be drastically different.
As crank length increases:
  • More flexibility/ range of motion is required.  
  • More core strength is required to resist losing a neutral spine due to the forces exerted by the lower and upper body. 
  • More upper body strength is required to counter the high force exerted by the muscles of the hip and legs.
As crank length decreases:  
  • Less flexibility/ range of motion is required. 
  • Less core strength is required because it mainly needs to resist the muscles of the lower half of the body (pelvis and below).  Don't get me wrong... this doesn't mean no core strength!
  • Less upper body strength is needed because the forces exerted on the pedals are too small to sway the bike. 
Long cranks have more physical requirements than shorter cranks.  REQUIREMENTS is the key word.  If you lack just a little bit of one of the three bullet points, you must get a shorter crank, otherwise injury is inevitable.  Keep in mind that a shorter crank is only a temporary solution that only buys more time until injuries creep back up, so be sure to correct any imbalances that you're aware of.  If you have or had an overuse injury, then you can be certain that you need corrective exercise.

People who ignore their body get caught in a counterproductive cycle of going shorter and shorter and shorter...  It's a solution that only addresses the symptoms, but not the source of the problem.  Contact me to set up a consultation for local private training or long distance coaching.

CRANK LENGTH & SPRINT PERFORMANCE
As crank length increases, sprint power output increases drastically.
As crank length decreases, sprint power output decreases drastically.
If your crank is short, you can expect an extra 70-100 watts per 2.5mm of length.  This is due to the fact that the body can more instantaneously apply maximal force than it can spin from X to Y cadence.  This extra potential power is the reward for preparing your body to push a long crank efficiently and safely.

I often get the question:  What about track cyclists?  If you look at the famous track racer, Mark Cavendish- he uses a 165mm on the track and a 170mm on the road.  This is also the case for every track racer who goes through crank optimization testing.  They tend to go up by 5mm from their track bike.

SO... WHAT'S THE OPTIMAL CRANK?
While planet internet is determined to find the holy grail of crank length, the answer is that one crank length can't do it all.
"One crank length can't do it all."
If you're not on top of your imbalances, injuries will happen.  When injuries occur, a short crank helps with rehabilitation.  If overtraining occurs, having a short crank available is beneficial to letting the heart and the entire body recover.  Progressing back to a long crank is how cycling rehabilitation should be done.  I own three cranks for this purpose and recommend my clients to have multiples too.  Consider it as an investment in preventative and rehabilitative care for your body.

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