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.”

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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.”

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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.”

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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.”

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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.”

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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.”

Our take

Shorter cranks: more aero and more comfortable

Shorter cranks: more aero and more comfortable

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.”

  • Erik Van Bommel

    As a long time eBayer all I see coming out of this article ‘ like a lot of stuff written and ‘researched’ at helping amateurs go faster is the price of 170mm cranks etc will go up. Buy now and invest in your child’s future.

  • xuxumatu

    it´s easy longer cranks are easy to push but harder to spin faster, i do not think that shorter cranks are better, i think the correct size is better

    i have trained with 165 , 170 172.5 and 175 and believe me 2.5 mm makes the difference

    why i like little bit longer crank arms:

    well first of all I’m a climber with a pretty good tt skills and after testing all these sizes i use now 172.5 and my height is 170cm now 42 years old

    well nobody is taking about age and metabolic efficiency , when you are very young, you have a lot of hrm range to spin faster, but the truth is when you have the ability to spin fast a longer crank it´s easy to do on a shorter one, a shorter crank may be better for you if you are young and do not have developed peddling technique, but in my young years as many pros that use longer cranks now, there were no compact cranks or large gears so you replaced them with larger cranks, so you learned to spin faster on longer cranks, may be is about train peddling technique, but now i prefer 172.5 and using lower gears so my heart rate is lower and better for my age, when you are a climber or a tt you know the less peaks are better so longer cranks may you stay on your sub maximal power output easier another fact nobody talks about is fast twitch fibres, thath not every one has the training to use them.

    so my advice is believe in your body if you fell good there´s no new theory that can change that

  • Frank Day

    Inches, the number of inches the bike moves per crank rotation, is a good number to represent the relative leverage from the crank to the ground that includes both gearing and wheel size but it ignores the number of inches the foot moves in the same rotation and a whole host of other variables that can affect performance. And, what is right for you may be entirely wrong for me. These one size fits all “formulas” based on who knows what just cannot be very good. Certainly there is no evidence that any of these formulas are worth anything.

  • RobTM

    Yes Frank, I agree.. when don’t get the physics right and add layers with biology and biomechanics, they just doesn’t make sense. Physical mechanics are a foundation.
    I never saw anywhere an understanding about effective gearing implications of crank length for instance. Numbers like “inches” is used, or simple sprocket rations without considering wheel size & crank length which are treated as fixed quantities. At end of the day, we move our feet to move on a bike, by using leg muscles; that motion absolutely has to be efficient and comfortable 🙂

  • Frank Day

    The problem is this is a lot more complicated than just physics (which, I agree, many cyclists don’t understand those relatively simple concepts). It also involves biology and biomechanics. Humans are not steam engines or electric motors. Power is generated by muscles. Different muscle types have different capabilities depending upon fiber type and how they have been trained. Training to maximize power generally hurts endurance and vice-versa. Further muscles have an optimum contraction rate for generating power which is the basis for their being an optimum pedal speed. Further those muscles must work through joints that further affect their efficiency in generating power. It is very complicated and no one (including me even though I have put a lot of effort into understanding this stuff) understands the best way to put it all together.

  • RobTM

    Firstly, again.. use gears, if it’s too high for speed change down. If you want to go faster, gear up so your cadence is right.
    Well I think people stand to avoid changing down on short rises, some do fail to anticipate the gradient, but seriously MOST experienced riders will use both sitting & standing on any long climb, even if they favour sitting as the posture change relieves lower back muscles for example.
    Well yes, I have wondered myself, those who mentioned using short cranks haven’t unfortunately included their inside leg measurement. I would expect the longer cranks to suit taller riders, shorter smaller ones.
    Without asking questions, we’re left only with sketchy articles, apparently written by people who don’t understand physics.

  • Frank Day

    It just seems to me that just riding “a little slower” isn’t the best choice when one is racing. The whole idea, it seems to me, is to optimize the racing experience.

    We can, I guess, disagree on why cadence drops when people climb. Seems to me that most people’s cadence drops because they are not geared properly for the climb they are on and this is the reason they get out of the saddle.

    Doesn’t it seem strange to you that riders and bike frame sizes vary about 30% yet crank size varies about 6% (165-175) and everyone seems to think that is enough? All those bike fitters measure all those angles then do nothing to optimize them (if they even knew what was optimum, which I suspect they do not).

  • RobTM

    Most riders can just rider a little slower rather than be “too fast” because of excessive pedal speed or change down.
    Cadence drops on streep climbs, because they stand up. I can spin well up such at 90-105rpm for example, but am far more comfy 2 gears higher when stood up. I try and sit mostly but also stand, as it emphasises different muscle groups.
    Thanks for the enlightening info, I have had a precision bike fit, but reducing crank length wasn’t something they considered, do remember lots of cheking on knee angles for position tweaks.
    I agree people don’t seem to apply basic physics, unfortunately that appears to lead to the blinding with pseudo-science sound bites, which need questioning when they appear in articles.

  • Frank Day

    For any given situation (10 sec, 1 min, 10 min, 1 hr, 5 hr, etc) there will be an optimum pedal speed to optimize power or endurance (or some combination) for each rider. Riding too high a gear at optimum pedal speed simply increases bike speed which will increase power beyond optimum for that rider which will fatigue the rider too fast. Gears allow the rider to approach that optimum if they know what it is. It is clear to me that most don’t have a clue how to do this or they wouldn’t let cadence drop to 50-60 on those steep climbs and wouldn’t ride at 110 cadence when cruising. It is a complicated situation but, IMHO, the smart rider spends time figuring out what works best for them for all these situations. Most don’t. They simply ride the cranks that came with their bikes and think more is better. More is better but smarter is better still.

  • 1970greenie

    “It found that maximum power changed by less than four per cent. If there’s all but a negligible difference in power,…”
    HEY!!! 4% is HUGE! That would be 16 watts at the level the pros produce on a climb!

  • Chris

    We all rode tubulars on UK Time Trials with a spare strapped to the saddle. No following cars allowed!. I never knew anyone who employed a mechanic, we all built and prepared our own bikes. We also knew how to do our own bike fits. Life was simpler then.

  • blair houghton

    Maybe it is BS. Or maybe the development of carbon cranks made stiffness plus weight reduction more valuable.

    But most of us aren’t riding $20K weight-weenie bikes with every possible efficiency improvement on them, so it’s not a given that we’d all be riding the best thing possible no matter how exotic. Anyone who rides glue-ons who doesn’t have a pro mechanic and a follow car is pretty much adding avoidable effort and risk to get a nominal but incontrovertible performance benefit.

    UCI would ban them anyway.

  • RobTM

    The pedal speed issue is what gears are for, longer crank can push higher gear for same pedal speed. A deep squat knee bend means body weight acts further from the pivot of knee so increasing the force required to lift, that seems like a poor example.
    Knee angle efficiency makes sense, though there must be an optimum for any given rider. This must be the core reason to prefer a given crank length.
    Power, means the torque force has to act over time, and too small strokes would allow too little time for muscle to work effectively by contracting, before they must begin lengthening again.

  • Frank Day

    Shorter cranks can increase torque by both decreasing pedal speed and keeping the knees in a more optimal position (the more the knee is bent the less leverage it has). If your current pedal speed is not optimum on the too fast side then shortening the crank can reduce pedal speed. It is easier to apply increased force to the pedal when it is moving away from you at a slower speed than if it is moving rapidly. Plus, if your knee is at a more efficient angle you get more force out of the same muscle contraction (can you lift more weight doing a half squat or full squat?). If pedal force increases relatively more than crank length shortens then both torque and power can increase. It is all a balancing act trying to optimize the amount of useful work the muscles can do in propelling the bicycle.

  • Frank Day

    If longer were better infinitely long cranks at zero rpm would give maximum torque. The data of Martin is clear, there is a wide range where power is hardly affected but if one is either too long or too short then power goes down. Again, according to Martin, the most important variable in generating power seems to be pedal speed. Whatever your crank length you can achieve optimum pedal speed by adjusting cadence appropriately. The major benefit to most when they go shorter comes from improved aerodynamics.

  • Frank Day

    Congratulations on being willing to experiment for yourself and giving PC’s a try. The torque on the hills issue is easily answered through gearing. Shorten crank length 10% all one need do is ride a 10% smaller gear (20-22 cog) and total torque to the road is exactly the same.

  • Chris

    I borrowed a set from my LBS back then and could not tell the difference from normal 170’s other than I got ankle rub. If the concept had been proven, we would all be riding them today. It was BS then and probably BS now. I’ll stick to my 170’s and round rings.

  • blair houghton

    I don’t know. Treating the crank as a rigid object, its shape is utterly irrelevant. But it’s not rigid, nor is the frame in which it’s spindling, and its shape can change how things flex. The USCF results could be perceptual; it’s not clear. The article doesn’t say what the MIT folks found out, and science doesn’t care about hints. So did they prove anything?

  • Chris

    Read the article again. What do you think?

  • blair houghton

    Well? Did the MIT professor’s strain tests prove anything?

  • blair houghton

    At infinite RPM, they would be.

  • blair houghton

    “better RPM, and this can improve pedal torque and help to eliminate any ‘dead spots’ in your pedalling action”

    Huh? All three things occur, but I don’t think they’re causally related, rather, they’re all three results of the crank length and maybe gearing change. If RPM went up and torque went up, and there was no gear reduction, you’re putting way more power into the stroke, but there’s no indication power is going way up. But they say they kept the same gearing. If RPM went up and power and gearing were the same, torque went down. But that would imply less power to the wheels. But they’re not seeing power drop. Which means all of this improvement is coming from lower wind resistance, not mechanical efficiency. Lower wind resistance means more speed for the same power. And more speed for the same gearing means faster RPM, and at the same power that means less torque. They’re results, not causes.

    Dead spots are reduced because the range of angles that the lower leg and foot have to cover is much smaller on a shorter crank. Nothing to do with RPM or torque.

  • it’s funny, you’re given the data in the article, and you’re still in disbelief. it’s like being shown a satellite photo of the earth as obviously spherical, and you’re still going, how can that be? it’s so flat! LOL

  • reece46

    It’s one of the few non-negotiables for me now, inside leg 30″ and 165’s made a huge improvement to knees and climbing efficiency/performance. Inconvenient but worth it, even the fit experts who downplay crank length will obsess over 1-2mm of saddle adjustment, why -because it’s cheap and easy.

  • David Sundheim

    I too am a sprinter (the Bane of being a 225lb 1/2 German 1/2 Norwegian, I can’t climb worth a darn) I was on 175s for 3 years. I switched to 172.5s when I bought my Power2max crankset.

    While I can’t say I feel any difference, can see the difference in how certain things have gotten easier, for instance I have noticed on climbs I can stay seated a lot longer, where I used to stand almost as soon as the slopes began. I also have a slightly higher cadence 10-15rpm, thought that could be cause I have really been working on it, too, its hard to say how much was the Crank and how much was concentrated efforts. Just my observation anyway.

  • RobTM

    That’s actually a very small 1.5% difference, it’s very odd you’ld perceive “a lot less leverage”. If you’ve moved your saddle up by 2.5mm, then at top stroke, surely your knee is only 2.5mm lower? The difference in distance between knees ought indeed be 5mm, double the crank length.

  • RobTM

    I think it’s just a bit easier to spin slightly shorter crank arms, so you perhaps can use a lower gear. More pedal resistance, means more leg force can be applied, perhaps that’s confused with “torque”?

  • Gordon Morris

    Yeah, you are right. If you go from 172s (my road bike) to 170s (my track bike), your saddle goes up by 2.5 mm to compensate for the change in distance from saddle to pedal, but at the top of your stroke your knee will be 5 mm lower.
    A couple years ago I tried 170s on the road. I found it felt very different; I could spin it up fine on the flats but on hills I felt I had a lot less leverage.
    The irony for me is that I’m a sprinter, so while I theoretically could benefit from shorter cranks at maximum speed, longer cranks benefit acceleration, which is also key. As it suggests in the article.

  • blemcooper

    Seems to me the 2nd expert fitter’s opinion is right on the mark, while the “shorter is better” mantra is just as silly as any other unqualified, universal statement when humans are involved. If “shorter is better” is all there is to it, then 0 length cranks would be perfect!

  • James McDiarmid

    I tried Frank Day’s powercranks a couple of years ago. I bought the adjustable length ones and ride them at 135mm for a while. On a flat TT course they are faster – less torque for the hills though

  • factor41

    I thought the same. I can understand that spinning faster can give higher power output, in the same way a high revving F1 engine has low torque, but high power at high RPM. Would imagine the torque per revolution would be lower though, unless there’s some weird positioning benefit which comes from not having to raise your knees as far?

  • RobTM

    How would shorter cranks increase torque? Force x distance, means a shorter lever needs more force on it for same turning moment. Longer cranks reduce the effective gearing, as your feet move further for same distance wheel travels, than with a smaller diameter circle moved with shorter ones.