WorldTour teams including Team Sky appear to believe that shorter cranks are more efficient. Marc Abbott considers whether we should all make the change
When Tour de France winning teams find a new way of working, it’s always worth paying attention.
Team Sky have for some time been testing their riders on cranks shorter than 170mm. Although it’s unclear exactly what length cranks they’re racing on, it seems the days of 172.5mm and 175mm cranks are gone.
The aerodynamic advantage of shorter cranks is widely agreed on among bike-fit professionals. Phil Cavell, whose CycleFit company performs pre-season bike fits for Trek Factory Racing, says: “With shorter cranks, the rider’s torso can be positioned lower because the shorter crank keeps the hip open. This has the knock-on effect of preventing unhelpful and inefficient pedalling adaptations due to hip impingement.”
Chris McCann of Inspired Cycling agrees: “Shorter cranks allow you to lower the torso angle of a rider with no negative physiological effect.
“Hip flexor angles can be eased and this can have a positive effect on the rider’s ability to breath better, as the diaphragm is not as affected. Lower back angle can be achieved.
“Some research has shown a decrease in the riders’ blood pressure, and this can have a positive effect on physiology. Short cranks can also protect riders with knee issues.”
A 2001 study by Professor Jim Martin (yes, this debate has been raging for a while) sampled tested power output in training cyclists using cranks of between 120 and 220mm in length. It found that maximum power changed by less than four per cent. If there’s all but a negligible difference in power, how else are shorter cranks aiding our performance?
McCann explains: “Mainly, the benefits include better RPM, and this can improve pedal torque and help to eliminate any ‘dead spots’ in your pedalling action.”
Cavell adds: “For a given gear, to maintain peak power your cadence will increase as crank length decreases.”
Scott Tomkinson of Kernow Physio (kernowphysio.co.uk) accepts the clear and present advantages of shorter cranks: “Riders can reap the benefits of a more open hip angle at the top of the pedal stroke, both in a road and TT position. Ultimately, a more open hip allows more engagement of the gluteal muscles when the pedal is in the three o’clock position. Thus, more forward momentum can be achieved without increasing muscle fatigue.”
However, he also points out, “You could argue for longer cranks for sprinting situations where you’re sustaining an out-of-the-saddle effort for one or two minutes — even something like a hill climb — as there are now a few studies that show a small benefit in this.”
He continues: “Any change in crank length should be in conjunction with an assessment by a professional bike-fitter.”
Beyond the flat-out world of time trialling, there are advantages available to every road cyclist, our experts agree. McCann explains: “The better pedalling efficiency and torque afforded by a shortening of cranks can help riders who struggle when climbing in the saddle and are always searching for that smaller gear.”
When asked if there’s such a thing as too short, Cavell echoes Tomkinson, explaining: “The length should be dependent on hip ranges first and personal taste second; anything under 160mm takes some getting used to.”
McCann says: “The ideal crank length can be determined by measuring the rider’s anatomy, mainly femur length, tibia length and a measurement taken from the heel to the ball of the foot. From this, you can study the leverage of the leg and find better fulcrum points. Measuring power and torque can also help.”
Arguing against shorter cranks is going against the grain and expert opinion. Offering better aero efficiency, increased comfort with no loss in maximum power, the question is: do I care that much to drop a sizeable sum on a new chainset? Although using cranks 170mm and under is better, spending time with a bike-fitter to find your optimum length is key.
Yes: Phil Cavell, CycleFit director, bike-fitter on the Trek Factory Racing team
“At CycleFit we have been passionate advocates of shorter cranks for over a decade. The science and research now confirms our stance. Shorter is better.
“We should all probably use shorter cranks for TTs and also general road riding. In five years, we all will. It’s like the long skis of the Eighties and Nineties… we all use shorter skis now.”
No: Scott Tomkinson, physiotherapist and bike-fitter at Kernow Physio
“It is down the rider’s needs and how it feels on the bike. Many riders prefer longer cranks, many don’t. There are many reasons that shorter cranks make sense, but as a qualified bike fitter and physiotherapist, I’d say that crank length selection is ultimately down to the rider’s personal needs, which can be ascertained only through a detailed examination by a professional.”