Why Cyclists Are Switching to Shorter Cranks for Efficiency

I am no engineer but one thing I retained from high school physics is that, over a fulcrum, a longer lever will lift a heavier weight. This logic was applied to cycling cranks in the 70s and 80s where it was thought that a longer crank will result in more force being applied to the chain for the same amount of power. Most bicycles came off the shop floor with crank lengths based on the size of the bike. So, a smaller bike, would have shorter cranks because the rider would be shorter and not have legs the same length as the rider of a bigger bike. Many thinking cyclists however, changed their cranks, even if they were of a shorter stature, because they surmised that the longer lever would be an advantage. This thinking is changing.

More and more cyclists are now moving to shorter cranks and many of the World’s best are using much shorter levers than the old formulas would have prescribed, based on their height. This new way of thinking probably began as a result of the ever more aggressive time trial positions adopted by road cyclists and triathletes. Athletes were trying to get lower and lower to reduce their frontal area but we can only go so low before our knees are smashing into our chests on the upstroke of the pedals. Not every cyclist has the flexibility of a gymnast, especially in the lower back, glutes and hamstrings. This is only made worse by the hours and hours of pedalling spent hunched over handlebars, trying to hide from the wind. Fitting shorter cranks means the knees don’t come up so high but also that the pedals don’t go down as low. So, the saddle can be raised accordingly, giving even more clearance at the top of the pedal stroke and allowing a greater differential between seat and handlebar height as well as between the knee and the chest. Win, win for aerodynamics.

Concerned time trialists were however worried that they were going to compromise power with the shorter levers so, testing was done. What we have now, that riders didn’t have in the 70s are power meters. So, the force that we apply to our pedals can be accurately measured. Thousands of tests have since proven that there is no reduction in force through the pedals as a result of shorter cranks. In fact, because the hips don’t have to extend as much and the pedals are moving in a smaller circumference than they would with the long cranks, riders are able to maintain pressure on the pedals for more of the pedal stroke, which actually results in better power outputs.

Then riders started wondering if shortening the cranks on their road bikes would not be a good idea as well, and it was discovered that there are a number of changes, as a result of shorter cranks, that could provide worthwhile improvements on the road bike.

Firstly, aerodynamics – Not as critical in a bunch as it is solo, on a time trial bike, but there will always be occasions where we are pushing the wind in a road race. Shorter cranks allow higher seat positions and the potential for increased seat to handlebar differences. This then produces lower frontal areas and more aerodynamic body positions, which are way more important than aero frames or even aero wheels.

Better ground clearance for the pedals – Shorter cranks raise the lowest position of the pedals in relation to the road. This will allow safer cornering and increase the number of corners we can pedal through. Maintaining power and speed through a corner means faster exit speed and either makes it difficult for riders to stay on our wheels through the bends or, it makes it easier for us to stay on the wheels of riders who have to freewheel through a tight corner.

Higher cadence – This is probably the most significant difference when fitting shorter cranks to our road bikes. Moving our feet around the pedal stroke at the same speed we were used to with longer cranks, will result in a higher cadence with the shorter ones because our feet are travelling less distance. A higher cadence is simply more efficient, although there are still those, especially in the triathlon community, who will argue otherwise. Power is what produces speed on a bicycle and power is the result of torque and pedalling speed. To increase power we need to either increase the amount of force that we apply to the pedals or, we can increase the speed that we turn those pedals. Increasing cadence is easier and more sustainable than increase torque.

Moving our feet in a smaller circle as a result of shorter cranks is also biomechanically easier and more efficient. This will allow us to increase our cadence with less metabolic cost than would have been possible with longer cranks. Simply put, pedalling faster will not increase our heart rate, and therefore energy demands, as it would have with longer cranks.

More power with less cost… sounds good to me.