The inspiration: In a classic case of tradition overriding logic, triathlon bikes are typically built with cranks that are the same length as road bikes cranks. There is no good reason these lengths — 170mm for small bikes, 172.5mm for medium-size ones and 175mm for large frames — have become standard, but bike fitters have come up with a very sound biomechanical explanation to go shorter. Bike fitter and coach Mat Steinmetz did a case study for Triathlete on Mirinda Carfrae and found that riding cranks 1 centimeter shorter allowed her to lower her aerobars by 2 centimeters (thus adopting a more aero position) without impinging her hips.
In practice: The tri-only bike brand Quintana Roo is one of the few companies that includes short cranks on its stock bike builds. In 2014, every tri bike from the brand will come equipped with a crankset that is 5mm shorter than the default length based on frame size. The size L CD0.1 comes with 170mm crank arms, the M is 167.5mm and the smaller sizes are spec’d with 165mm.
The Spanish crank manufacturer Rotor was the first to offer crank arms that are substantially shorter than the average, and they’ve gone even shorter in 2014. For the extreme early adopters looking to go dramatically shorter, the Rotor 3D+ crankset is available as short as 150mm.
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