“There’s a massive elephant in this room. And that’s crank length. This is a massive issue and one that can be resolved swiftly.” The words of former Team Sky bike-fitter, and physiotherapist Phil Burt back in the winter of 2021 when I was analysed, man-handled and manipulated by the burly Cornishman for my 2022 goal event of L’Etape du Tour, which I documented in my book Riding with the Rocketmen. Burt recommended dropping from my standard 175mm cranks to 170mm, even 167.5mm. Why?
Well, the hips don’t lie and for many months mine had been voicing their disapproving truth: that creaking into the aero position was simply not sustainable without a perma-grimace. So, I went with Burt’s advice, dropped the crank length, opened up the hips and voila – a still moderate but pain-free cyclist. Little did I know at the time that the likes of Tadej Pogačar and Remco Evenepoel had clearly been tracking my progress with both now using shorter 165mm cranks, Pogačar dropping from 172.5mm in 2023. Ineos Grenadiers are reportedly keen on speccing short cranks, too. So, what gives? After years in the darkness, why is the neglected crank enjoying its moment in the sun?
Cut drag and injury
“For a multitude of reasons,” says bike-fit pioneer Phil Cavell. We’re sure many of you know Cavell, especially if you reside in the south-east of England. Cavell is joint-founder and CEO of London-based Cyclefit. He works with amateurs and professionals alike, including female and male riders at EF Education Pro Cycling, and wrote the hugely successful ‘The Midlife Cyclist’. (As you’ll discover, he also now holds the honour of becoming my first interviewee to use the word ‘antediluvian’.)
“For someone of Pogačar’s standard, it’s about efficiency,” Cavell says. “It means at the top of the pedal stroke, he’s more fluid, which is because he’s created more space thanks to a double win. You see, when you shorten your crank length, broadly you increase saddle height by the same distance. So, if like Pogačar you drop by 7.5mm, you raise your saddle height by 7.5mm. That means he has 15mm of extra room at the top of the pedal stroke, so he can adopt a deeper drop position for greater aerodynamics. He’s obviously been well advised as we’ve been banging this short-crank drum for over 20 years.”
“Increasing hip range is key as long cranks introduce too much knee and hip flexion at the top of the pedal stroke, meaning you scrunch up, which can cause hip and knee issues,” adds Cavell. “Shorter cranks open you up, making things more comfortable, especially if you’re not flexible. And that accounts for many of us. As we age, we only grow stiffer and tighter; you don’t tend to grow older and more flexible.
“We also find that many riders who’ve come from a pretty high level of high-loading sports when they were younger might see limited hip ranges, too. Sports like rugby, football and hockey can lead to tight hips and hamstrings.”
With my 2021 Burt assessment, I’d thought my stiffness, ever apparent on the dance floor, was the result of years of football leading to brittle hamstrings. I still play five-a-side in a 47-year-old’s vain hope of being the new Bryan Robson. As it transpired, my hamstrings were surprisingly flexible, said Burt. Unlike my hips. “I’ve never seen stiffer,” he said. It’s why both Burt and Cavell extol the merits of shorter cranks in search of easing and preventing injury.
Supported by research and fighting dogma
And that means comfort. And a comfortable rider is a fast(er) rider, supported by a 2021 study in the International Journal of Exercise Science that showed shorter crank length improved economy for novice endurance athletes. The rather extreme bandwidth between longer and shorter cranks – 175mm versus 145mm – saw the 14 riders boost efficiency accompanied by a 3-5.5% increase in power output with the 145mm cranks. “These improvements may be related to the slower pedal speeds, slower muscle contraction velocities, and more extended hip and knee joints that a short crank length affords” the paper concluded.
A further 2021 study in the European Journal of Applied Physiology estimated that the optimal crank length for sprinting is around 20.5% of the cyclist’s leg length. Leg length is around 45% of height, which would imply an optimum crank length of about 9.2% of total height. That would put the ideal crank for someone of average male height (175cm or 5ft 9in) at around 161mm or 150 mm for the average female. These are rough numbers but with further studies suggesting less metabolic cost to similar power outputs, too, it’s clear that there’s a persuasive argument for going short.
Which begs the question, why have longer cranks like 175s been the bike manufacturer’s spec of choice since time immemorial? “A common argument was that longer cranks offered more leverage, meaning more torque can be generated,” Burt told me. “This is true, but leverage comes at a cost. If you can move your pedal with a certain force and at a certain speed around the circumference of the pedalling circle, a longer crank will generate more torque but at a lower rotational speed because the circumference is bigger.”
“Dogma,” adds Cavell. “You’ll always see something like 175mm cranks on a 56cm. Bike manufacturers have always had this conservative approach to go long with cranks and wide with bars. But you’re not fitting a spider. You’re fitting a human being.
“I come from a motorcycle racing background. If you want to increase power, you don’t increase the stroke length of the engine. No one ever tuned a motorcycle engine by giving it a longer stroke because it'll self-destruct. If you want a motorcycle engine to generate more power, you find a way for it to rev harder. And the way to do that is to lighten the components and reduce friction in the system. You’ll then have more power because power is simply torque multiplied by revs.”
Increasing your cadence
That revs aspect brings us onto cadence. If we refer you back to study one from 2021, the increase in performance from shrinking to 145mm cranks came via an increase in cadence of over 14rpm. “That’s in order to have equal pedal speed due to the pedal circumference difference between the crank lengths,” the paper read.
Cavell explains. “If you’re like Pogačar and dropping down from 172.5mm to 165mm, you must compensate for that drop in pedalling circumference. In this case, you’re looking at a 7.5mm drop so, referring to your school days, you’re looking at a drop in pedal circumference of two multiplied by Pi multiplied by the radius, which in this case is that drop in crank length of 7.5mm. That means around a 5cm drop in circumference, meaning a higher cadence and arguably higher gearing is required to balance things out.
“If you’re pulling the crank down by two or three per cent, you’re going to need to increase their cadence by two or three per cent to keep the power the same. So, if you’re pedalling at 90rpm, you might need to increase it to 93 or 94bpm. That’s not a problem for most people but a few might struggle with the change. I’d tell them to persist, but shorter crank length isn’t for all.”
This persistence, adds Cavell, is given a nudge by data. “Pogačar and his team would have undertaken what we call an A/B test. Simply, this is fixing one variable – in this case heart rate – while changing crank length and seeing the power output at different heart rates. We do it here and it’s a good test to enlighten the sceptical riders.
“We also take subjective feedback: how does it feel? Inevitably they’ll respond ‘shit’ but we’ll say, well look, your heart rate is the same but your power output’s higher. That’s very powerful for a rider. They’re then engaged and might proceed to tell you that their back’s not hurting anymore. ‘Well, you didn’t even mention a bad back,’ I might respond!”
You can still go long
Cavell and Burt are short-crank missionaries. But that doesn’t mean traditionally longer cranks don’t have their merits, Cavell says. If your body’s tuned into long cranks and you’ve adapted to “a slightly more compressed set-up” at the top of the pedal stroke, then arguably stick with them.
“And there’s a strong argument for an explosive rider like a criterium athlete staying long. You’re making your living changing pace really quickly, so your instant power needs to be high. As power output’s essentially torque multiplied by revs, you want that torque figure really high. Can you spin the crank round quick enough with a shorter crank to compensate for less torque? It’s a trade-off but maybe not.
“I’m working with a Paralympian who’s competing in para-triathlon. I’ve got them down to using 160s, which is pretty short. The course in Paris is twisting and technical, meaning lots of accelerations and decelerations, so I’ll be to blame if she loses!”
Cavell adds that it can also be tricky convincing taller riders of dropping in crank length as they’ve got used to ‘that’ feeling. And logic obviously suggests that great height equals great crank length equals personal best? Think again.
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“Three weeks before Bradley Wiggins’ hour record [in 2015], he was using 177.5mm cranks,” Burt said during my 2021 makeover. “Everyone used to think a tall lad with their long legs needed long cranks. It’s not true. Wiggins, who’s 6ft 3in tall, was so low his knees were coming up into his chest and close to his elbows. So, I suggested he drop to 170mm cranks. Steve Peters [psychiatrist who’s worked with British Cycling and Ineos Grenadiers] used to call him the leopard because they don’t change their spots and Wiggins wasn’t a man easily persuaded. But Bradley asked Steve and we all agreed to give it a go. So, we dropped him from 177.5mm to 170m, dropped his front end by 10mm and enjoyed a 3.5% improvement in CdA [measurement of drag]. And that’s the man who’d won the Tour de France!”
“The way I see it,” Burt continued, “if I ask you to jump onto this one-metre-high box or this 4mm box 100 times, I’ll give you £100. Which would you choose? Of course, the lower height. Crank length makes a demonstrative difference to your cycling comfort and, ultimately, that’ll make you a better cyclist.”
There we have it, your party-political broadcast for the short-crank party. Are you convinced? Should you change? Back to Cavell and his next step. “What are the challenges you’re looking to solve or are you just curious? If it’s curiosity, there’s not the same pressure so, if budget and mechanical skills afford, you can play around with crank lengths, remembering to adjust your saddle height and then see how things like power are affected via the A/B test [this is easier if you have a smartbike like those from Wahoo, which have space for pedals at different crank lengths]. Do you feel better or worse? The problem with this approach is that you didn’t evolve to ride a bike. It’s an abstract environment, so the body tends to give bad feedback.
“If there’s a problem you’re solving – whether that’s improving performance, preventing injury or eradicating pain – then I would see a professional, like ourselves or other bike-fitters. Either way, we know that today’s cyclists are far more engaged in the crank-length debate. Long gone are the days when we were talking to some kind of antediluvian mechanic.”
