While most riders obsess over gearing, tyres, or saddle height, the length of their crankarms quietly influences how they produce power, their bike fit, and even how fast they can go.
For decades, crank length was just what came stock on a bike. Few riders questioned whether 170, 172.5, or 175 mm actually made a difference. It was an almost-standardised part of the setup, rarely scrutinised beyond a basic sizing guideline tied to leg length. However, in recent times, this has begun to change.
Ronan Mc Laughlin
Beneath this seemingly simple component lies a subtle but powerful variable that affects how your body interacts with the bike. Elite pros like Tadej Pogačar, Jonas Vingegaard, and Filippo Ganna have embraced shorter crank arms, with Evenepoel and Pogačar going 1-2 in the Tour de France's stage 5 time trial on 165 mm arms. The trend in the pros is sparking renewed interest across the cycling world. But what’s really driving this shift?
How does changing the length of the crank arms alter your pedaling mechanics? How does it affect the force you apply, your cadence, and even your bike fit, for comfort or aerodynamic benefit? And beyond performance, what role might it play in reducing injury risk?
Understanding crank length isn’t just about choosing between a few millimetres of arm length; it’s about exploring the interplay between biomechanics, power production and physics, including an aspect that often goes overlooked: gearing.
How does crank length fit into the broader system?
Between your pedals and the power being laid down on the road are a lot of variables, with crank length being just one of them. There's also the force applied to the pedals, pedaling cadence, gearing, and tyre circumference, all of which play their role in how your muscular force is converted into power and forward momentum.
At the core of cycling performance is power: how much you can produce, and how efficiently you can deliver it. The more power you can produce, the faster you travel over any given terrain, and crank length factors into the equation. Crankarms are effectively levers, which, in this case, can be seen as force multipliers; the longer the lever, the more torque you generate for the same force at the pedals.
If you apply a force of 200 Newtons on a 165 mm crank arm at 90 rpm, you generate 311 watts; applying the same force on a 175 mm crank at 90 rpm produces 330 W. Of course, in the real world other variables come into play, but fundamentally, crank length does have an effect on the force you apply at the pedal, and the power that translates to.
On paper, longer cranks seem to give you more power for the same force, but that overlooks one crucial variable: foot speed.
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