Could shorter cranks help you crush the bike and save your legs for the run?

A winter spent grinding on the indoor trainer will have made you a stronger cyclist. As the body changes and adapts each year, so too should your bike fit.

One of the best ways to improve power, aerodynamics and comfort is a proper fit. With spring just around the corner it is a good time to adjust your bike to be ready for outdoor riding. It’s worth considering if shorter cranks should be on the list of upgrades.

Shorter cranks reduce the distance your foot travels to make a single revolution. Imagining the circle your foot must draw during a pedal stroke. The length of your crank arm determines how big that circle is. Proponents of short cranks argue that having a shorter distance to travel to make a single revolution has benefits.

The shorter the crank the smaller the revolution

Consider cadence and how it is impacted by crank length. If both riders take one second to make a full revolution, the rider with the longer crank will have to have a higher cadence in order to match the timing of the rider with a shorter crank. A higher cadence produces a higher heart rate. Many in triathlon will argue that riding with a high heart rate will ‘burn a lot of matches’ and leave you spent on the run. A shorter crank will give you as many revolution as a long crank but at a lower cadence, and possibly a lower heart rate.

One of the big gains for going short is the opportunity to lower cadence when racing. This keeps the heart rate in check and saves your matches for the run. Many pro athletes and high-profile coaches have shared data on the cadence they held in competition. Three-time Ironman World Champion, Mirinda Carfrae, was known to hold a cadence of 82 RPM in Kona. Her coach, Siri Lindley shared that this was the sweet spot for Carfrae when combining the power she needed on the bike and the juice she needed on the run. Carfrae runs 165 millimetre cranks.

Carfrae was not only a multi world champion, she was a standout on the run. She still holds the 2014 record for the fastest run split in Kona, with a time of 2:50:26. Carfrae’s cadence would be considered on the low end for a cyclist. If switching to a shorter crank could help you comfortably ride 180 kilometres at 82 RPM and save your legs for the run it might be worth considering.

Cadence changes affected by various factors

Ironically, many athletes who switch to shorter cranks report that their cadence actually increases. It is possible that this is due to maintaining the tempo of their established cadence, and when transferred to a shorter crank produces more revolutions. While some argue that a shorter length reduces the leverage available to force the bike forward, the impact is actually quite small considering other factors. Adjusting the gearing can offset this factor to produce more power, weakening that argument.

Finding the correct crank length isn’t straight forward. Saddle height has to be considered in the equation. A bike fit with a higher saddle would run longer cranks to fit the same ratio as a bike with a lower saddle height. Individual factors like leg length, rider size and flexibility need to be factored in when arriving at the correct crank length for you. Shorter cranks can also have a positive impact on comfort, power output and aerodynamics.

A fresh bike fit can improve your spring riding

Most bikes will come with a standard crank length of 175 millimetres. The assumption is that this is the ideal or preferred length, but in fact it is simply the standard that was arrived at eons ago and remains the customary component on new bikes. Crank arms are available in lengths as short as 150 millimetres, suitable for smaller riders. A qualified bike fit professional can assess all the factors that need considering to determine the optimal length for you.