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  • dllm

    I think longer cranks can have more leverage at very steep slope (1x%) that some cyclists have to resort to biggest cog and the cadence is still only around 50. Other than that I think crank arm length doesn’t matter too much to performance directly.

    I agree it’s about fitting more than performance but how to determine the best length? I hope someone could lecture us…

    • Hexsense

      which you can compensate by shifting gears.

      more leverage but take longer to complete a circle
      or
      less leverage thus need lower gear but have smaller circle circumference which lead to higher cadence.

      that’s how crank length effect gearing.
      imagine 53/11 on longer crank which your max cadence is 110.
      but with 50/11 on shorter crank which increase your max cadence to 120 (both smaller circle and better bio-mechanical movement) . 50/11 at 120rpm is faster. With that, you gain 34t chainring to aid climbing vs 53/39. etc.

      things gone ugly if you compare long crank with 34t and big cassette already to a short crank though. There is just not low enough gear to move to.

      • dllm

        Yes, I agree that switching gear saying.

        But my case is that the rider is already at the lowest possible gear, so longer crank will have more leverage.

        Apart from the fact, how one values the leverage (with minimum use case) is… up to everyone to decide their own.

        • DaveRides

          Except that the switch to a longer crank may make their pedal stroke less efficient or put them at risk of injury if their legs aren’t long enough to fit the longer cranks, in which case they should keep their current crank and instead think about changing their cassette.

          • dllm

            Yes, but when they fit then the longer arm more leverage stands. Again, it really depends on fit or people.

    • Alex Simmons

      As Hexsense says, the cranks are not the only lever available to you on a bicycle. This article below by Tom Anhalt about his personal experiment of riding a steepish hillclimb on both 175mm and 150mm cranks illustrates this pretty well:
      http://bikeblather.blogspot.com.au/2014/07/crank-length-whateverwithin-reason.html

    • Tom Shield

      Just like car engines, riders will be either torque limited or power limited in any given situation. Steep climbs or acceleration from stopped are both torque limited cases and then a longer lever arm will help. If you are power limited then both force and speed are involved and crank length just trades off between the two with little effect.

      • dllm

        this is the best explanation.

        • Tom Shield

          Thanks. I should have added that changing gears lets you pick which limit you are at until you run out of gears one way (low cadence lacking torque for steeper climbing) or another (high cadence lacking power for higher speed).

      • ShawnBot

        Respectfully (and I may be wrong), I don’t think it’s so simple.

        Ex: Steep climb -> torque limited, as you say. A longer lever arm will definitively help, is the assertion made.

        Sure. Except if that longer lever arm puts you outside of your efficient range of motion.
        Which a longer crank arm on a very steep climb can well do. Very much more noticeable out of the saddle, under full effort.

        One length creates punchy pedal strokes, another (longer) creates the feeling of thrashing around or swimming through longer strokes, i.e. ‘going too far’ between top and bottom of that stroke to feel efficient.

        There’s just a whole lot of body mechanics and dynamics involved. For sure you have a longer lever but you also have a larger travel circle, greater distance to cover under a fixed muscle firing rate. Maybe that fixed firing rate just isn’t applicable to the length of time it takes you to travel around that circle. Switch gears? Maybe. But also maybe your body is too contorted in the high/low leg positions to develop the torque you otherwise could.

        This is my experience for the last two years after switching to longer cranks. Haven’t been able to train my way out of it.
        So it seems like a biomechanical interaction, which adds up, rationally, to me — but I’m not a student of this.
        Thus I won’t make any claim to a higher truth! :D

        • Tom Shield

          I was only commenting about why crank length has an effect in one case and not the other. I was not intending to imply anything about fit, which does seem like the more important thing to worry about.

  • Andy B

    I personally feel Q factor is more important in respect of performance

    • Great point, Andy. There’s a piece in that, for sure.

      • Alex Simmons

        My UK colleague Xavier Disley did a study on this:
        https://www.ncbi.nlm.nih.gov/pubmed/22612455

        • Wily_Quixote

          Link Broken – full thesis available here:
          http://etheses.bham.ac.uk/5523/

          • Alex Simmons

            Thanks, although the PubMed link seems to be working OK for me.

        • Andy B

          Very comprehensive Thanks for sharing

      • James Huang

        Add it to the list, Matt!

      • FrankDay

        The Q argument makes no sense to me. First, can anyone come up with a mechanism to explain why narrower would be more powerful or efficient? But more importantly take a look at weightlifters, do they narrow or spread their feet when trying to exert a lot of force? In addition, an argument can be made that bringing the feet closer together might increase wind resistance. Worrying about Q just seems so much like worrying about how many angels can dance on the head of the pin.

        • Alex Simmons

          Frank, cycling is not weightlifting. If you really want to use a poor weightlifting analogy, you need to assess stance width of single legged squats ;)

          I’d suggest reading the above linked paper for some clues but I’m not holding my breath given your track record.

          As for aero, narrowing Q factor can go either way, or neither.

        • Andy B

          From personal experience across many bikes with different q factors I know that not having the right setup effects comfort, pain and power output hugely (for my body)

          This will come down to how adaptable you are but personally if the q factor isn’t right, my power and endurance is affected

  • Finx

    I’m very tall and long legged, but have quite a lot of leg strength. I have a fairly low cadence at ~85 or so. I can manage crank lengths anywhere from 170mm up to 180mm, but settled on 175mm and it’s working fine for me (I do use XT 180mm cranks on my hardtail MTB).

    However, I have a female Asian friend who recently bought a new bike. It was an XXS frame, basically about as small is you can get (she’s 5′ tall). The bike came with 170mm cranks, which were way too long for her. Her hips and knees were bent at uncomfortably tight angles, and she ended every long ride with sore knees.

    We had some 155mm cranks made for her (cut down aluminum cranks from Bike Wright) and it was like night and day watching her ride after that. Her cadence was up and her HR was down. She could ride much more comfortably and much longer with these shorter cranks. And best of all, NO MORE KNEE PAIN!.

    Some people are just more sensitive to this ‘setting’ than others. I could probably get on just about any bike and make a good day of it, assuming proper seat height relative to the bottom of the pedal stroke. But people with shorter than average legs are going to have much more difficulty trying to adapt to a relatively large pedal circle.

    • mcalista

      What kind of manufacturer specs 170mm cranks with a XXS frame??? It should be obvious that if someone is buying an XXS frame, it is because they are “height challenged” (no disrespect to your friend), and the cranks should be sized accordingly.

  • Wily_Quixote

    I went to 165mm cranks on my road bike to accommodate a hip injury.

    Shorter cranks mean less trunk/femur angle at the top of the pedal stroke which assists my capacity to keep cycling on a road bike.

    Not that I am concerned about performance these days but, as the research states, there are no performance disadvantages to a shorter crank. I went to compact gearing at the same time so the gear ratios are relatively preserved.

    • Velt

      What’s your inseam/height?

      • Wily_Quixote

        my height is 173cm no idea what my inseam is but my trousers fit at 32 inches.

        I had to go to flat MTB pedals as well, unfortunately

        • Velt

          Hmm, I’m the same height but usually go a 30 inch leg. Might have to look into a 165mm crank. Thanks!

  • Jim

    I thought there was something to do with foot speed being important, so longer cranks you pedal lower cadence and shorter cranks you pedal faster but that in the end the crank length that enables your highest foot speed is the crank length you are best off with.

    any thoughts?

    • Alex Simmons

      It’s more helpful to think in terms of circumferential pedal velocity (CPV) since this relates to muscle shortening velocities. Same cadence on different crank lengths means a different CPV. IOW to achieve the same CPV, cadence is higher on shorter cranks.

      • LeeRoy

        I’ll admit I’m extremely “limited” when it comes to understanding anything physics related but I wonder whether pedal/foot speed is a factor for racing in Junior categories where the gearing is limited and the only “lever” that can be changed is crank length? The argument is that the longer the crank the greater the foot speed required to achieve a given time/speed over a certain distance (say, a flying 200). Therefore, in junior cycling, where footspeed is a big factor, wouldn’t you be better off on shorter cranks…assuming you can smoothly pedal a higher cadence…as most juniors can.

  • Alex Simmons

    Nice item. There are many perpetual myths about pedalling, crank length, cadence and so on.

    One other factor to consider, which comes under the heading of bike fit, is the potential for gaining an aerodynamic advantage by modifying crank length as this *may* enable a rider attain more aerodynamic body position. It can be a double-edged sword though, as while a shorter crankset might enable a lower front end set up, it usually also requires an increase in saddle height and these two factors can work against each other when it comes to the impact on aerodynamics. It’s a classic case of something that’s individually variable to be assessed on a case by case basis.

    • Wily_Quixote

      How would a higher saddle increase drag? The area of leg presented in the frontal plane is the same with a higher saddle and a shorter crank as a lower saddle and shorter crank.

      All that is being changed is knee angle of the leg at full flexion, this still presents the same frontal surface as before. Leg extension at the hip is unchanged at the bottom of the pedal rotation, so how is it possible that the new position affects surface area of the leg?

      We know that a lower trunk and head angle is possible with a shorter crank so, overall, frontal surface area should diminish with a shorter crank. the only element of the bike/rider complex that is lengthened is a couple of centimetres of seatpost.

      • DaveRides

        If you think simply in terms of frontal area, a longer crank would give a slight reduction on the area of the leg at the top of the stroke, as the bottom of the raised leg would be higher up.

        But aerodynamics is about much more than frontal area, so you would need to test that in a wind tunnel to check for sure. Even if you could confirm it did give an aero improvement, it would need to be weighed against the impact on the pedalling action.

        I think it was Tony Martin who had an “improved” position for time trialling a couple of years ago and went back to his previous one because it was restricting the amount of power he could put down.

      • Alex Simmons

        Note I said it *may* increase drag. I know this because I’ve tested it on various riders (I regularly test cyclists’ aerodynamics) and for some lowering the saddle results in a reduced CdA (in one case it was worth about an extra 0.3km in an hour record).

        As we know, CdA is the product of both Frontal Area (A) and coefficient of drag (Cd). The former is fairly straight forward to understand and is a measurement of the cross sectional area an object presents to the air flow. Cd (at similar Reynolds numbers) is essentially a function of an object’s shape (and surface roughness and various complex interactions regarding boundary layer and flow separations). Every time you adjust a rider’s position on the bike, you are likely making changes to both Cd and A and hence may impact their aerodynamics. This is when computational fluid dynamics (CFD) analysis can help to visualise what’s going on but nothing beats aero testing to ascertain the actual impact.

        Changing saddle height may or may not impact rider power and comfort, which is why this is still a fit issue. Once you change saddle location, you generally also need to adjust the front end set up as well. Fit impacts comfort, power, stamina and aerodynamics. Optimising the combination for the target event is what we’re after (e.g. what’s best for a 4km pursuit, a 40km TT and an Ironman is likely different as the specific demands are different).

        In my experience, the shape the rider assumes can have quite sizeable aero impacts, and changing saddle height and crank length can impact the shape the rider assumes.

  • Stewie Griffin

    “The cost of a new crankset will be better spent on formal training with a coach.” Try explaining this to all triathletes out there spending €12k on equipment but find a coach too expensive..

    • FrankDay

      If your equipment is sub optimal for you then you are simply limiting your potential and the cost of a coach is also somewhat wasted.

      • Stewie Griffin

        Sub optimal… if you can only put out 180 watts for 2 hours, good luck riding your bling tri ‘optimized’ setup for 6 hours in an ironman.. Fit to bike & fitness first, before optimizing your rig. I’ve been coaching some triathletes together with my brother, these guys are going to Kona. But it is striking that they find $100 a month expensive one day & then spend $2500 on wheels the next day. Mind you, we spend on average 4 hours of analysing and finetuning their schedule on a sunday and are always tracking their training efforts. On average over a year their performance improves 15% (depending on their baseline), more improvement than any wheelset

    • Luis Lopez

      Stewie I have seen this at many ironman races, men with beer bellies 120kg, riding bikes with disc wheels and teardrop helmets, they are after quick solution, they will walk the whole marathon, swim bike & Walk, nothing about being an athlete and only achieving a bucket list. you have to understand that they have different goals like recreational cyclists, commuters & elite riders.

      • Stewie Griffin

        Although I find these iron men of 120 kg in some way admirable, it’s not pretty healthy way of going at it and I’m pretty sure every doctor would not approve. I do sometimes wonder if the admission to ironmans should do more medical screening. They too, would benefit in investing in a coach for 6 to 8 months, losing X amount of weight and ride a less expensive setup and end the race more comfortably. A more cost effective and healthy way of achieving their bucket list. But then again, we (still) live in a free world, don’t we?

  • oonnoo

    I used to use 170mm cranks on my road bike. Then I started track riding and I felt much more comfortable in every way especially the drops but couldn’t put my finger on why. I eventually realised the main difference between my track and road bike were the cranks. 165mm on the track bike. I then fitted 165mm cranks and the road bike and have never looked back. I have more space between thigh and stomach in the drops and just riding over flyovers or small hills is much different-I barely notice the inclines in comparison to the 170’s. Climbing is nicer. The top dead centre is almost unnoticable too. I am 170cm tall with shortish legs so this is probably why I notice so much difference.

    • slowK

      I recently went from 170 to 165 mm cranks too (but I’m 5’3″/160cm). I should have done it years ago, but that’s what my bikes came with. So far, no downsides. Saddle raised 5mm to compensate, more comfy in the drops (as you say, less thigh getting too close to torso), less toe overlap, and just more comfy overall.

      I’m still just as slow and pathetic though.

  • Steven Andrews

    The scope of material acquisitions to worry about and blight an otherwise superb bike ride is simply without limit.

  • FrankDay

    I would like to point out one thing regarding the Martin study. While indeed he found “no difference” between 145, 170, 195 that was a scientific “no difference” when, in fact, there was an obvious trend and the highest power was seen with 145. If there had been more people in the study it is quite possible there could have been a “significant” difference. Plus, he didn’t do the study with the riders in the aero position or correlate to rider size.

    We have been encouraging people to experiment with this and have found that about 80% go substantially shorter with most of those settling on crank length between 135-155.

    • Oldan Slo

      “While indeed he found “no difference” between 145, 170, 195 that was a scientific “no difference” when, in fact, there was an obvious trend and the highest power was seen with 145. If there had been more people in the study it is quite possible there could have been a “significant” difference. ”

      Either that or your ‘obvious trend’ would be different. The Martin data shows a small trend and large standard deviation. I would suggest reading ‘Statistics for Dummies’. ‘Fooled by Randomness’ is also another good book.

      • FrankDay

        ??? Statitics for dummies? One doesn’t have to be a PhD in statistics to see trends or understand issues with small sample size. There was an obvious trend in the data but the power of the design was inadequate to determine whether the trend represented something real or not. The error Martin made in that study was in the discussion/ conclusions where he said there was no difference when he should have concluded this needs more study. Edit: because of that conclusion this study is erroniously used to argue that crank length has been proven to make no difference. It does no such thing and actually raises more questions than the one it didn’t answer.

        • weiwentg

          I am a statistician, so I will bite.

          There is an obvious trend in the data. They showed that mean power with 145mm and 170mm cranks was higher than 120 and 220. Fine, so we can assume that few riders would want to have 120 or 220 cranks.

          However, they can’t conclusively show that the highest mean power is generated at 145mm. The difference between 145mm and 170mm is very, very small. They can’t distinguish mean power at those two crank lengths with their sample size. The difference between 145 and 170 is so small that unless they have a physiological theory for why peak power might be optimized with cranks quite a bit shorter than 170, I would say that yes, there’s an absence of evidence that peak power is at 145 rather than 170.

          That said, this is frequentist stats. We can only assert an absence of evidence here. We can’t assert an evidence of absence. So, again, was there a physiological argument?

          Side note: They went and fitted what I assume is ordinary least squares regression with some polynomial terms. They used a correct method (repeatedly measures ANOVA) for the first analysis, which accounts for the fact that they’ve got repeated measures on 16 people, not 16*4 independent measures. It’s not clear that their regression analysis accounts for that fact. Methods are available (linear mixed effect model, or generalized estimating equations).

      • Alex Simmons

        Oh, what a shame. Cycling Tips has become infected with the Frank Day virus.

        • FrankDay

          Why don’t you offer some perspective and facts to the discussion rather than ad hominem bs. A pretty good article deserves serious discussion and back and forth.

          • Alex Simmons

            I have done exactly that to other comments that make sense Frank. Somewhat in contrast to the nonsense you bring everywhere you show up.

  • FrankDay

    I’d also like to make a comment regarding crank length formulas. There are so many variables affecting proper crank crank it is impossible to have a one-size-fits-all formula. Power – more power should require longer crank length. Flexibility – the more flexible the rider the longer the crank length they should be able to ride. What kind of riding / racing do they do- The aero position will generally require a much shorter crank. At Cetra. The only way to really know what the best crank link for someone is is for them to experiment on themselves with the kind of riding they do. This takes time. It should also be done before one gets a bike fit in my opinion.

  • Ali89

    “… For those riders with greater cardiovascular strength, a shorter crank works better because they tend to ride at higher cadences.”

    Couldn’t this lead to a Chicken & the Egg argument; I thought crank length played a part in determining cadence?

    • FrankDay

      two things should determine cadence but another thing does for most people. Higher cadences are needed for higher power and shorter duration efforts. Lower cadences for lower power and long duration efforts. Sprinters putting out 1500 watts for 30 seconds will be at 140-160 cadence. A 30 minute tt effort at 400 watts may be best at 100 while at 200 watts best at 85. Then there are the long distance races where cadence drops even more. What most people do though is try to emulate their favorite pro even though they may be putting out only half the wattage. Do what is best for at your level of training and for the kind of riding you do.

      Edit: let me try to clarify a bit. At any given power and duration there will be an optimum pedal speed. This combined with crank length will determine your best cadence. But, also, for any given duration there will be an optimum cadence (sprinters have faster turnover than marathoners) so this is another basis for finding your optimum crank length so you can race at both the optimum pedal speed and reciprocation rate for the kind of riding being done.

  • Mike Szwaya

    What I don’t see in the study is the % of inseam length that these crank sizes are (145mm to 200mm). To me, that’s a more appropriate correlation. They note that poor results are at the extreme ends – which I get. But I’m 6’6″ with a 36″ inseam. I have observed, in real training & racing settings, that riding anything at or below 170mm produces less power.
    I generally ride 175’s and 180’s if I can find/afford them (I haven’t gotten motivated enough to get Zinn custom cranks yet). I do know that when I get back on the bike(s) with 180’s, it’s like…ahhhh sweet. It feels like I can use a fuller range of motion with the longer cranks.

    • FrankDay

      That is just one of the problems with the study. We must assume his riders were around average in the 5’9-10″ range. Conventional wisdom would suggest that 170 is probably best for them but the Martin study suggests that much shorter is better. Doesn’t prove it but suggests it. Many of my customers who have done this testing have gone shorter, substantially shorter, but not all. One about your size settled on 200 primarily because he lives in a mountainous region. Lots we don’t know about crank length.

    • Alex Simmons

      There is a section in the Martin study discussing crank length to leg length ratios as well as for femur length and tibia length (each was measured). “Second order polynomial regression analysis was performed to determine the optimal crank length (as a ratio of leg length, femur length and tibia length) for maximal cycling power”. I’d invite Jim Martin to the conversation but unfortunately with Frank here sucking oxygen I doubt he could be bothered.

  • Luis Lopez

    I’m a lifetime athlete, 30 years of ironman racing, some years ago I looked into using a shorter crank and took this seriously, I went from 170mm to 165mm, I even tried 175mm before hand. I have 770mm inseam / 169cm tall, I was able to improved PR on the Bike 20 years later at the age of 47, also the course changed and more difficult. efficiency is more important than little accelerations as I pay for them later on in the race.

  • bugwan

    Don’t tell anyone, but I was so desperate for a power meter about 18 months ago that I bought a Stages, 172.5mm one. I forgot my drive-side is 175mm.

    I’ve been riding different crank lengths for a year and a half without issues (so far).
    *awkward emoji*

    • FrankDay

      2.5mm is such a tiny difference that It is unlikely anyone could tell the difference on blind testing. Doctor ignore leg length differences this size because they are considered normal

  • pervertt

    I’ve never understood why bikes have to come with cranks of fixed length. Why don’t more manufacturers follow LOOK’s example with their Zed crankset, where crank length can be adjusted between 170 – 175mm. That way you can experiment without having to replace a perfectly good set of cranks.

    • FrankDay

      170-175 is a 3% difference in length. Riders can vary as much as 30% in height (or any other variable you can think of) so that is hardly much of an experiment.

      • pervertt

        Wasn’t suggesting that a Zed crankset would resolve all sizing issues. 170-175mm would probably cover the most popular crank lengths among riders. For anything much shorter or longer, a new crankset would probably be better.

  • David Alexander

    I’ve found crank length most relevant when it comes to saddle height. I have very long legs and a comparatively short torso. Most endurance frames don’t have enough stack; I end up in an aggressive forward lean and, with a typical 73D seat angle, my weight way over the back of the bike. A set of long cranks (and low-stack pedals and a cleat-back contact point) allows me to bring the seat down enough that a borderline frame can start to fit. It’s an expensive fix, though. Used cranks over 175mm are somewhat rare.

    • FrankDay

      Can’t stack height be increased? Or a longer stem if you are too far back?

  • Dave

    Let’s face it, for 99% of us, whether you ride 165mm or 175mm cranks or anything in between, the torque advantages are close to irrelevant. Ride what fits and treats your knees well.

  • xuxumatu

    too much blah blah for explain a simple concept: shorter leverage needs more cadence less muscle travel longer leverage needs less cadence more muscle travel.

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