Should you be using shorter cranks? Bike fit experts increasingly recommend a change away from the accepted wisdom of yore, especially for riders with hip issues, time triallists and anyone who wants to get into a really deep tuck. We spoke to the two Phils of bike fit, physiotherapist Phil Burt and Phil Cavell of London’s CycleFit studio, to find out why.
Here’s the executive summary of why shorter cranks — meaning 165mm for a typical adult male rider — are a good thing according to the experts:
- They enable a deeper, more aerodynamic riding position for sprinters and time triallists
- They allow more fluid, comfortable pedalling
- They can reduce or eliminate lower back, hip and knee pain
- For triathletes the transition from cycling to running becomes easier
- Shorter cranks can even make your saddle comfier
For literally decades the accepted wisdom in cycling was that male riders of average height should be on cranks that are about 170mm or 172.5mm long.
But in the last few years a quiet revolution has been underway, with bike fit experts recommending shorter cranks for many riders. What’s going on?
> How to fit new cranks to your bike
Some advantages of shorter cranks have long been known. If you don’t lift your knees as high as you pedal, you increase the angle between the bones of the leg, the femur and tibia, and that can reduce the peak load on the knee, reducing the risk of injury. Similarly, shorter cranks open up the angle at the hip and depending on your riding priorities that can allow you a deeper tuck for the same hip angle or a more comfortable pedalling action if you have any hip problems.
But it was long thought that there was a price to pay for all this: shorter cranks meant less leverage and that in turn meant less power.
Phil Burt (Alex Whitehead, SWpix)
Phil Burt was lead physiotherapist at British Cycling for 12 years and consultant physiotherapist for Team Sky for five years. He now has his own bike-fit and physiotherapy practice, Phil Burt Innovation, which has brought him into contact with hundreds of ordinary riders like us, as well as the elite cyclists he used to look after.
The crank length revelation
In his recent book Bike Fit he writes: “I've had a suspicion that crank length is the elephant in the bike fit studio for a long time and, although we saw the aero benefits of shortening cranks for time trials and pursuit during my time with British Cycling, since working with a wide range of riders I've really seen the impact it can have on both comfort and power production. This almost Damascene realisation … regarding crank length is probably the most significant and impactful thing I've learned since working with a broader range of cyclists.”
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Burt explains the research that led to experts like himself taking another look at shorter cranks: “Paul Barret who was the biomechanist at British Cycling and is now head of performance at Team Ineos, did his PhD with Dr Jim Martin and they were looking at whether crank length was actually relevant to power. We all grew up believing that if you’re bigger, with longer legs, you need a longer lever, so you can match that to your power. Well, they totally blew that apart.
“It’s relevant in maximal cycling, which is what Chris Hoy does in the first two revolutions of a team sprint, but it's not what me and you do at all. So once you uncouple crank length being relevant to power, why wouldn't you not manipulate it?”
In his book, Burt cites his favourite example: “The analogy I often use with clients is, if you had a one-metre plyometric box and a 15-centimetre step and I offered you £100 to jump onto one a hundred times, which would you pick? Of course you'd want to pedal a smaller circle and shift any problems to your gears rather than your ankles, knees, hips and lower back.”
Phil Cavell, co-founder of London bike fit specialists CycleFit, agrees, explaining that the discovery that shorter cranks don’t affect power, “liberated [bike fitters] because what it meant was that crank length became a function of two things. One is hitting your flexion ranges and the second is your taste, what you like.
“What we find is if someone's got a hip flexion constraint, if you shorten their crank length by five mil or seven mil they just pedal better, their pedal stroke becomes way more fluid. Their body's not compensating and adapting around this biomechanical constraint so you get more power more evenly in a safer environment. So their knees don’t hurt, and particularly their hips don't get injured.
“So in one sentence, short cranks is very safe and protective of your body. That's the kind of big takeaway there.”
Burt points out that long cranks can actively prevent riders from being comfortable and attaining an optimal pedalling rate. “Quite often people will say to me, I really struggle to get up to 80, 90 cadence. That's because they’re on a massive crank length and it closes the hip up at the top. So it causes discomfort and they wobble around.”
What are the benefits of shorter cranks?
One group of athletes that have embraced shorter cranks is the swim-bike-run crowd: triathletes. “We look after British Triathlon’s fit process,” says Burt, adding that triathletes are much more open to changes like this than dyed-in-the-wool club cyclists. “So I look after the Brownlees and Alex Yee. When we went in, we made a similar shift down in crank lengths with those people.
“They found that dropping crank length helped them hold a more aero position and a better position, but when they're transitioning to running, they felt much freer. You can translate that to anybody who’s got a lower back problem.”
There are knock-on aerodynamic benefits too. In the run-up to the 2016 Olympic Games in Rio, Burt says he and Team GB’s support squad made the decision to put riders on 165mm cranks.
“Bradley [Wiggins] heard that and said to me ‘I should change.’ And he was on 177.5mm cranks and he dropped down to 170mm in one go, then 165mm the next day. He dropped his front end 30 millimetres and got a three and a half percent drop in CdA [drag coefficient] on the track. That's a man who won the Tour de France right? Well, you wouldn't say he had a bad position would you?”
Wiggins of course went on to be a member of the pursuit team that beat Australia in the final in Rio, landing him his fifth Olympic gold medal. That was despite Burt and his team saying that Wiggins shouldn’t make such a big change in one go. Dealing with elite riders, says Burt “you become very risk averse to threatening someone's performance,” but he now says “I'm yet to meet a rider who wouldn't benefit from shorter cranks.”
Of course it’s not just a matter of a change of cranks, there will be other adjustments to your position depending on what you’re trying to achieve. You’ll want to raise your saddle to accommodate the shorter cranks, and perhaps your handlebars too, or you might leave them where they are and take advantage of the deeper position you can now achieve.
You might even find your saddle feels more comfortable. “With shorter cranks, peaks in saddle pressure are reduced and I've seen many riders experience a significant reduction in saddle discomfort by reducing crank length,” Burt writes in Bike Fit.
How can you tell you need shorter cranks?
What if you think everything’s fine with your current crank length? Is there any way to tell if you might benefit from shorter cranks? Hip pain or any other hip problem is the big giveaway, but Phil Cavell says there’s a more subtle tell.
“In the absence of any pain or discomfort, what they might find is that as they get to the top of the pedal stroke, their knee is abducting, and that means going to the outside. If one or both knees are moving laterally to the outside, at the top of the pedal stroke that's a sure sign that there's a constraint and a shorter crank might be more comfortable, more efficient, etc, etc," he says.
"So that'll be the biggest takeaway, that’s our biggest telltale, if you like, that there's a constraint there.”
Cavell also has strong advice for anyone who has a known medical hip condition: “Anyone who's had hip issues, impingement, an accident or an injury, or they've got a family history of hip replacements, or partial hip replacements, all those people should preemptively look at a shorter crank.”
Are there any downsides?
Because switching to shorter cranks means you’re going to have to pedal faster to produce the same power, it won’t work for a few riders. Phil Cavell explains: “Some people have a problem with cadence that they can't lift their cadence from [say] 87 to 91, for whatever reason, then they are going to lose a bit of power. There's no need for them to lose that power if they've got an extremely good hip inflexion range. So if someone’s got a great hip inflexion range, but they do have a tendency to low cadence, why change their crank? The longer cranks are almost certainly going to work better for them.”
If you do switch to shorter cranks, you can expect an adaptation phase as your body gets used to the new position, but it might not take as long as you think.
Phil Cavell says: “Generally going from 170 to 165, there’s a very short adaptation phase. It can almost be at the end of the [bike fit] session.
“At the end of the session, they're done, they're fine. They’re acclimatised and for some people, it’s an epiphany. They were cycling in pain, they feel discombobulated, they feel uneven and wonky, and then you put them on a shorter crank, and suddenly they can pedal better. So for them the adaptation is really rapid. But for other people it can be a bit longer. If you go from 175 to 165 that can take longer.”
These are minor downsides, so let’s give the final word to Phil Burt:
“Cranks are the most common component I change for riders who come to me for a fit, and the impact is often a game changer.”
Who makes short cranks?
One of the problems if you want to switch to shorter cranks is simply finding them in the first place. Most manufacturers offer 165mm cranks, but few list cranks shorter than that. Shimano goes down to 160mm for Dura-Ace and Ultegra 12-speed cranks, and Shimano 105 12-speed and 11-speed. SRAM offers just one 160mm road crankset in 12-speed Rival. Campagnolo doesn’t list cranks shorter than 165mm in any current groupset.
The most readily available shorter cranks come from smaller manufacturers who’ve specialised in solving fit problems or are addressing the triathlon market. Rotor Aldhu cranks come in lengths as low as 150mm, while if you want something a bit less spendy FSA Gossamer cranks are available as short as 145mm.
However, there’s a bit of a difference between what’s listed in manufacturer websites and what you can actually buy. 165mm cranks are reasonably easy to find, so, as usual, us average-sized blokes are okay, but smaller riders who might want to switch to 160mm cranks (a size Burt says is “completely appropriate” for smaller riders, who tend to be more women than men) or shorter are going to struggle.
In Bike Fit, Phil Burt writes: “Unfortunately, the bike industry is still catching up with the science and probably has a load of 175mm cranks that they still have to get rid of!”
He recommends Rotor as one of the easiest to source and having spent some time scouring retail sites I have to agree: You can just order them from Rotor. Similarly, you can order Gossamer cranks direct from FSA.
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