19 Apr 2016
HOW TO CHOOSE YOUR PERFECT CRANK LENGTH
They come as standard sizes on most bikes but different limb and torso lengths mean you might not be riding the most efficient crank for you.
Your crank is possibly the most important contact point with your bike. It’s where your fitness, energy and enthusiasm are channelled in the search of ever-greater speed. It’s also where art eclipses science because finding the perfect crank length for you is a very personal thing. And that’s why we begin by dispelling a myth: that an increase in crank length leads to more power. It doesn’t. Studies have shown that while they change torque, power is unchanged and they simply require the rider to pedal a larger circle. More important is comfort and, with that in mind, there are broad principles that you should adhere to.
Most modern bicycles come with cranks measuring between 170mm and 175mm depending on frame size. That might be okay, especially when solely gauging the foot in the six o’clock position. However, when it comes to crank length, it’s more important to note what’s happening with the foot at 12 o’clock.
If the crank is too long, for instance, it forces your knees to bend more. This can lead to a kinetic chain of events through to the hip and the lower back that, either instantly or over time, results in pain. It will also impact efficiency because you’ll find it’s difficult to sustain a good power output. It inhibits aerodynamics, too, because you can’t maintain a streamlined position because you’re uncomfortably ‘tucked up’ (see our feature here about finding an ideal aero TT position).
It’s a slightly different and shorter story when it comes to cycling with too short a crank length, as it shouldn’t cause injury and comfort should be okay, but you might find the naturally increased cadence becomes tiring or simply affects enjoyment.
That’s why it’s beneficial to calculate the ideal crank length for your size, and why Vision offer the Metron TT BB386Evo //product link// in five sizes from 170mm to 180mm, while the Trimax Compact TT MegaExo come in six sizes from 155m through to 175mm