Pick a crank, any crank
There have been many attempts to quantify the ideal crankarm length for cyclists of different heights. At just under 6’7″ (2.0m) I’ve been particularly interested in this subject. I’ve ridden cranks from 170-200mm on various bikes over time, and broken several sets in the name of experimenting.
This CyclingTips article collects some of the research highlights, including one from 2002 which establishes that “mechanical power output and pedal speed, a marker for muscle shortening velocity, are the main determinants of metabolic cost during submaximal cycling”.
In layman’s terms, that means that longer cranks at a lower cadence will have the same cost as shorter cranks at a higher one. This was confirmed in 2017 by a study that found that crank length didn’t alter metabolic cost, but cautioned that too-long sets could cause joint issues.
So in the end, as the CyclingTips article suggests, cyclists can feel free to choose a crank length based on what feels best to them. For me, that’s 195-200mm for hilly road rides to help with low-cadence torque; 180mm on the rollers for seated spinning; and somewhere in between for flat roads and off-road riding (where pedal strikes are a concern). Anything shorter–and even 180s when standing–feels like I’m Homer Simpson riding the clown bike.
Finding cranks outside the 170-175mm range is still challenging and expensive, but worth hunting down a pair to try, especially if you’re on the extreme end of the height spectrum.