Crank Length

What is Crank Length?

The length of the crank arm as measured from the center of the bottom bracket to the center of the pedal spindle.

Why does it matter?

Crank length can have an important effect on a rider’s biomechanics; a poor-fitting crank can negatively impact performance and result in injury to the rider.

While many bit fitters agree that crank length should be proportional to body size, there are numerous methods for determining ideal crank length and many cases in which a rider’s individual biomechanics require a deviation from the norm.

Aside from rider fit issues, longer crank arm length can also increase the risk of toe overlap and pedal strike.

Industry Trend

Most of the bike industry specifies proportional length crank arms that are shorter on smaller bikes and larger on larger bikes. Standard lengths for production bikes typically range from 165-175mm although shorter and longer cranks are available aftermarket.

Bike Crank Length Trend
The chart above shows the relationship between bike size and crank length for production road bikes. As bike size (Theoretical Rider Size) increases, so does crank length. However, the relationship is not linear, particularly for the smallest and largest bike sizes.
Bike Crank Length Heat Map
The chart above shows the % distribution of crank lengths for each bike/rider size (crank lengths from 160mm-180mm shown although calculations include all lengths). Note how, beyond a certain point, crank lengths don’t continue to scale proportionally to bike/rider size. It’s as if there is a virtual floor at 165mm and a virtual ceiling at 175mm that bike companies are reluctant to exceed.

Crank Length Options

Crank arm length exists in several places at Bike Insights.

Base builds
Customized builds
Default of 170

When calculating things like Toe Overlap, we will first use the default crank arm length in the base build (e.g. what a complete bike ships with). If a build is then customized, we will use the custom crank arm length for these calculations. If no values are present in either of the builds, we use the default value of 170.