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Shorter cranks can help you get comfortable in a more extreme aero position.
Hip angle—the angle between the rider’s torso and legs—might be the most important factor in determining a rider’s ability to comfortably produce power on a bike. Chances are you’ve experienced the significance of hip angle yourself. If you lower your shoulders either by crouching down or by dropping your bars, you will eventually reach a point at which pedaling becomes less comfortable and maintaining power is a struggle. Tri bike geometry is designed to help maintain a comfortable hip angle when riding in a crouched aerodynamic position, but even on a tri bike, all riders have a limit to how tightly they can crunch themselves at the hips. Raising the aerobars is the most common way to open hip angle, but this can compromise aerodynamics, handling and even limit the bikes you can ride. Crank length—not just frame geometry and aerobar position—impacts hip angle, yet most athletes riding triathlon-specific bikes are still using conventional road bike crank lengths. Mat Steinmetz, a Retül bike fitter in Boulder, Colo., measured the influence of crank length and aerobar drop on hip angle using Retül’s 3-D measurement system to see how crank length affects hip angle.
Although hip angle is typically measured between the ankle, hips and shoulders with the rider’s leg fully extended and the crank at the 6 o’clock position, hip angle at the most compact 12 o’clock position is the fit dimension that prevents most riders from lowering their bars.
Wider hip angle = more comfortable position
Steinmetz found that shortening the crank arms by 1cm opens hip angle by 2–3 degrees. Raising the aerobars by 2cm had approximately the same effect.
Use it yourself: If you are trying to lower your aerobars but can’t drop any farther, swap your cranks for a set with arms 1cm shorter and you might be able to drop your bars another 2cm below your saddle!
By Mat Steinmetz with Aaron Hersh