Why Your Mountain Bike Crank Length is Likely Too Long

Why Your Mountain Bike Crank Length is Likely Too Long

With few exceptions, most XC and Trail oriented mountain bikes shipped today come with 175mm cranks. While some brands spec 170mm cranks, it is often only on their smallest sizes. However, the evidence leans towards mountain bike crank lengths being too long in general. Why are current lengths not optimal for many riders and why isn’t anyone doing anything about it? Good questions. I only have answers to the first.

Why are Short Cranks Better on a Mountain Bike?

Here are some reasons why shorter mountain bike cranks should become the norm.

  • You don’t have to be Rachel Atherton to know how often cranks and pedals can strike the ground on high sag/low BB height trail/enduro based mountain bikes. With wide platform pedals, it isn’t hard to touch down once or twice even on some of the easier mountain bike trails around me in Vermont. Cranks striking the ground is not a good thing. You may not need a higher bottom bracket as much as you need a shorter crank…
  • While shorter cranks do create slightly higher gearing, shorter cranks accelerate through the top and bottom of the stroke faster than longer cranks.
  • There is no tangible maximal power loss to shorter cranks. One of the most respected researchers in cycling mechanics, Dr. Jim Martin, studied this very topic and published the results in 2001. https://www.cervelo.com/en/engineering-field-notes/a-new-spin-on-crank-length.  The bottom line is that most riders will not give up any power riding a shorter crank and many will actually gain a little.
  • Muscle Balance. I know I’m likely to get arguments on this one in particular, but if you truly want to maximize your power and efficiency, you want to develop a high cadence. Don’t want to believe me, talk to an exercise kinesiologist about the cadence characteristics that tend to define the most powerful and efficient cyclists.

Shorter cranks don’t increase your power on their own, but they do make developing a powerful high cadence stroke and accessing a broader range of muscle groups easier. In turn, this makes developing higher levels of sustainable power easier and creates more consistent traction.



  • Reduced Joint Load. Shorter cranks put less torque and load on joints and muscles, thus reducing the chances of knee, hip, back and other pain while riding your mountain bike.
  • The first mountain bikes were built from pirated road bike parts. Mountain bike crank length was simply transferred from whatever road bikes were using in the ‘80’s and haven’t changed much since. Road bike cranks are available in a lot more lengths than they were in 1985…

So, Why Aren’t There Shorter Cranks on Mountain Bikes?

  • Bike manufacturers need to start asking/insisting on more crank length options to be available if component manufacturers are going to start building them. I don’t think any/many bike manufacturers are asking.  They should.  I bet a bike where the crank doesn’t strike the ground on a demo ride sells better than one that does.
  • Not enough riders are asking for it. Just because we get used to something (like a certain length crank) doesn’t mean it is optimal.

Pro riders and bike manufacturers need to be the impetus that drives the change to shorter crank possibilities for XC and trail mountain bikes. While a few months of muscle adaptation may be required before the full benefit is realized, I encourage many pro mountain bike riders (especially those on the shorter side) to try a shorter crank. I would not limit this to just smaller riders either; a number of Team Sky’s pro road riders used shorter cranks this year on the road.

And to bike manufacturers, I ask why a 170mm crank on a 48cm road bike is almost universally considered unacceptably long today and the same is not true on mountain bikes?

Dogma is the Death of Innovation

Treating things as dogma goes against the spirit of innovation that has been a hallmark for the bicycle industry since before the Wright Brothers. A spirit that always looks for ways to improve the experience and the performance of riders.

For an industry that has put so much effort into changing axle or bottom bracket dimensions by a few mm, the laissez faire attitude on something that can potentially improve how a bike and rider perform as much as crank length seems strange.  The time for shorter XC/Trail MTB crank length options is more than here.

About Ian

From first time riders to Olympians, Ian has helped thousands of athletes achieve their cycling and triathlon goals. Ian develops much of the Fit Werx fitting and analysis protocols and is responsible for technology training and development. He is regarded as one of the industry leaders in bicycle fitting, cycling biomechanics and bicycle geometry and design. He is dedicated to making sure the Fit Werx differences are delivered daily and provides Fit Werx with corporate direction and is responsible for uniting our staff and initiatives.

Find out more about Ian Here


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38 Responses to Why Your Mountain Bike Crank Length is Likely Too Long
  • Dalton Bourne

    Replacing a bike crankset is needed whenever you discern signs of wearing and tearing on your component. Some indicators are knocking noises, a visible bent, or damage that could mean you have to purchase a newer one. The three factors to consider when choosing the optimal crank length you need are your height, cycling discipline, and preference.

  • jay

    this is what I’m currenty facing. my current groupset on my mtb is worn down and its time for an upgrade. my current bike has the stock 175mm cranks but figured now is the time to change.
    I am a 5″87 rider and tbh I occasionally get the hip and joint pain.
    I was first advised to save up for the groupset before going for a fit, now I’m left unsure of what to buy. should I go with 165 or 170?
    help me out please

    • Ian

      While I don’t know all the details of what you are doing and your situation, based on the hip and joint pain alone, I would go with 165mm. Except in rare circumstances, there just isn’t much downside for a rider of your height and a host of potential benefits.

  • Jonathan Hughes

    I am 6 2″. I went up a steep hill in Cazadero in northern California in a 39 – 21.I was using Murray cranks set at 155 mm. I would have bogged down with a 175 MM crank with those gears. I went on a ride with the Santa Rosa cycling club. They have strong riders. I was behind them going along Austin Creek Road to cazedero. I shifted into what was my lowest gear passing the riders when the climb started. They were surprised when they looked at me, going by with great ease. It felt like I was walking up that steep hill. One attacked passing me when I was at the top, aproaching the next climb. I went to attack putting more force to the cranks. The cranks could not stand the force, ripping in two. Murrey replace the cranks. The next problem was the clamping area for the pedals. It is made of compressed carbon. That did not hold up.

  • Grant

    Please read the comment posted a few minutes ago first……apologies. I left the reason out of my message on why I was reading your article in the first place.

    Post ride knee ache.

    Specifically not pain while riding but an ache that can linger for a day or two post long, hard rides or becomes particularly obvious during stage races. This discomfort is not debilitating, but a pain in the ar…knee. 😉

    I don’t feel any obvious set-up issues other than moving around on the saddle a bit, but that’s the norm when XC riding as far as I am aware.

    Thanks again.

    • Ian

      Hi Grant,

      I don’t think test riding crank length tells you much. Crank length effects where the rider has access to different muscle groups, but can’t force a rider to pedal one way versus another. For this reason, when you change crank length, you may feel a certain way about the change or feel you gain or give up power initially. The data says that these are temporary markers though and that the rider can adapt their muscle pattern and regain that power over time. What is more universal is that a shorter crank, within a reasonable range, can reduce joint loads for the rider. For this reason, I think a shorter crank is worth a try for your issue.

      Hope this helps.

  • Grant

    Hi Ian

    Several years down the track since you posted the original article, but thank you for writing one of the more informative and balanced opinions on the crank arm length topic.

    Being mountain bike specific and providing reason to your perspective makes me want to try 170mm crank arms on my Scalpel. 173cm ‘tall’ with a short inseam, approximately 78/79cm, I have been curious as to what difference I would feel, as well as potential power output changes.

    It’s just such a shame that these things are so difficult to try before you buy due to the limited options at the ‘local bike shop’.

    Thank you again.


  • Adam N.

    Thanks for this great article. I am 5’8.5″ and ride in rocky terrain almost exclusively. Pedal strikes are a constant for me and break up my flow and speed. While I am generally in good shape I do have some knee issues and I have thus decided to size my cranks down to 165. I’m glad I found this wile specing my new bike.

  • Michael Duval

    I’m a singlespeeder and have 1 bike set-up 175 (Misfit Dissent), the other 170 (Carver Gnarvester). Both 29ers. Tough to compare because of diff geometry, 1 bike has supsension fork, other rigid and also 1 bike geared for mountains (32:19 vs 32:18). At 5’11” and 32 inseam which length should I be moving towards?

    • Ian

      Hi Michael,
      The science supports heading towards the shorter length. If you look at what many track riders do, even tall riders are often on 170mm or shorter. This being said, there are a lot of different mechanics going on with a single speed on a mountain bike as your crank length becomes an even more integral part of your gearing. All else being equal, I would go with the 170mm. Hope this helps.

  • Judd

    I currently have a SWORKS epic with 172mm next face cranks. After many miles I developed hip impingement which permanently damaged my hip. I did tons of research on hip impingement and cycling. After much research I decided I absolutely needed to shorten my cranks. Because of my hip impingement syndrome I found only two companies that make custom short cranks. Canfield bicycle and Zinn cycles. I purchased 150mm custom cranks from Zinn. I’m 5’7 and normally I would of wanted cranks between 160-165 but because of my limited hip rotation I ended up with 150mm. Yes crazy short. These short cranks have been amazing and less stress on my hip and knees.

    • Ian

      As you noted, for those with significant chronic issues, going much shorter on crank length can be a real boon. In addition to the companies you mentioned, JCobb has offerings that start at 145mm while Rotor starts at 155mm. Enjoy!

  • ben

    I have a herniated disk in my lower back(l4-l5), and the is a big difference between different crank lengths. I am 172cm, and my 170mm is a litle bit too long, and after an hour my back hurts. when I use a shorter crank the pain is just gone. simple proof – the only problem is that when I want to buy a new bike, there are no options for the crank length. most are 175mm(mtb) standard, and I have to specifically find something that suits me better…

    • Ian

      Shorter cranks can help with such issues. Glad that is working better for you. Bikes are likely not going to come with cranks from the factory in the length you want. This is where a good dealer will work with you to get it set-up right with an aftermarket crankset. We view a bike as it comes out of the box as just a starting point. From there, changes almost always need to be made to help the bike match the rider’s needs.

  • Don

    Another rare diamond in a veritable (internet) sea of … stuff. Thanks for that.

  • Connie Epp

    Here is my dalama I am 5ft tall I just got an extra small trek rosco 8 mountain bike. It came with the normal size crank arm I have trouble standing up when needed with the longer crank arms, I was wondering if shorter crank arms would work better for me. I also just turned 72 yrs old.

    • Ian

      A shorter crank would make a lot of sense for your height and situation. While there are a lot of factors that could be playing into the trouble you are having standing up, the crank could be a part of that and it would make it easier for you on a number of fronts regardless.

  • Lp

    If I shorten my crank length, will I need to slide my seat back further?

    • Ian

      Yes, you would want to adjust your saddle up and back whatever the difference is between the existing crank and the new shorter crank. If you go down 5mm in crank length, raise the seat 5mm and push it back 5mm. Hope this helps.

  • Gregor

    Good story but the fitting Cool-Aid just is not a simple blanket of shorter is better. Like the title suggest. Many riders have pointed out some of the pitfalls. Yes some riders need longer cranks. Even if that means they might hit a rock from time to time. That’s like I gotta cut my bars down they don’t make it through the trees. Also not recommended! Very little science behind the short crank concept that seems to get replayed every 15 years.(Has an ironman ever been won by a man on 165 cranks?) If you could try three lengths and look at power, speed, heart, and cadence you might find the real story for the rider. It has all been tried before trust me. The real truth is there is very little difference but do your own test and see what it tells you. Cheers

    • Ian

      Hi Gregor,

      If the article wasn’t titled what it is titled, would you have even found it? The title says, “likely” and the article does not say that shorter is better for all. It states that, in general and on small to medium mountain bikes in particular, mountain bike crank lengths are disproportionately long and that they present some design limitations.

      There is a good deal of quality science on short crank and performance. The science demonstrated that maximal power was not harmed to go shorter for most riders and that joint load was reduced in most cases and many riders saw benefits in oxygen transfer. Look up the studies by Jim Martin (who I have spoken with and seen present at cycling science symposiums) and John McDaniel on the topic (the links in the article will get you there). This being said, I will agree that crank length can be a very personal topic and trends have come and gone.

      While 5’11” Craig Alexander won Kona on a 167.5mm crank, men winning Kona on shorter cranks isn’t relevant to the topic. The article was designed to point out that small to medium height riders in particular are riding disproportionately long crankarms on mountain bikes in particular. Regardless of height, 80% of the top 10 women at Kona in recent years have been on cranks shorter than 170mm. However, a woman buying a mountain bike won’t find anything below a 170 on their new bike and many will find 175.

      What it comes to bike fit and topics like crank length, addressing what tests best now is not always the best goal if you are trying to help someone improve as a rider. Sometimes you have to take a step backwards to take future steps forward. Modifying pedal stroke through crank length change is an excellent example of this. We’ve worked with many smaller athletes in particular who have always had to push disproportionately long arms (that is what all their bikes came with). Many, understandably, have a low cadence and struggle in the hills at least somewhat because of it. While the comfort benefits can be more immediate, when most of these people switch to a shorter arm they have an adaptation period where they have to get used to pedaling at a higher cadence and with different muscles before they see the speed benefit. People are adaptable over time, but tend to perform best at the moment doing what they have trained their body to do at that time. This is why power based performance assessments in bike fit is all but worthless. In an athlete riding a biomechanically reasonable riding position (within the normal ranges), if you want immediate performance benefits, you should spend a lot more time looking for aerodynamic improvements.

      The main point is that the available lengths on mountain bikes in particular are not proportionate to the range of riders being served. If you have a rider with a 80cm saddle height and another with a 63cm height (17cm of saddle height difference), should their crank length really only be separated by 5mm of crank length? In the mountain bike world, should everyone just be on 175mm as many brands seem to provide? I agree that there is more research that could be done on this topic, but my money and experience (and the science to-date) says that the answer is that how it is now is not optimal. There should be a bigger range available and it should be more size proportionate.

      This all being said, you say there if very little difference in performance across crank length. If this is the case, why wouldn’t you ride a shorter crank on the mountain bike for the reasons listed (less ground strike, the ability to design a lower center of gravity bike, etc…)?

      Thanks for reading the conversation. Ride on!

      • Christian

        Hey there Ian,
        I’ve just been trying to get a handle on crank lengths regarding road bikes by doing general searching and here you are on the topic!
        Most of my life, I’ve been a keen road cyclist, but since turning 50 back in 2011, I’ve gone MTB mad. I figured, since I had never crashed and injured myself on a road bike, it was time for a change!
        Anyway, sure enough, all 5 of my MTB’s in England and in Australia, have all got 175mm cranks. Seeing as I ride Black graded trails, with mainly platform pedals, rock strikes are a thing and so are tough climbs over long distances.
        Not to mention, at nearly 60, consideration for knee joints is due.
        My question is how can a shorter crank arm be easier to climb with? Don’t normal rules of leverage apply here, like, we use a longer handle on a tool socket for extra torque with less effort, to loosen a fastener, for example.
        Finally, does the theory apply likewise to road bikes?
        Cheers, Christian.

        • Ian

          Hi Christian,

          Good questions. I view crank length as something that helps make it easier (or harder) to access a specific muscle group at a particular point in the pedal stroke more than something that has significant bearing on maximal power generation. While longer crank arms can offer greater basic leverage at the front of the stroke, that can come at the expense of maintaining/increasing momentum through the rest of the stroke. I would never underestimate the benefit of momentum and higher cadence/RPM when it comes to going over obstacles and climbing efficiently.

          A shorter crank length on a road bike make it easier for the rider to access transitionary muscle groups at the top, bottom and back of the stroke and maintain a higher cadence easier. However, I suspect that the equation is complicated a bit by the more consistent and smoother motion of a road bike compared to a MTB. You are also less likely to dab a pedal on a road bike… This all makes the costs of momentum loss on a road bike harder to factor than it would be on a MTB going up a moderately technical climb.

          In the end, I would think about crank length as a way to encourage different muscles to be available at different parts of the stroke more than I would a method of absolute power generation. Per the study linked in the article, even when crank lengths were grossly disproportionate from current norms (really short arms with really long legs powering them and vice-versa), the biggest maximal power difference that was created was 12% when a crank length was changed by 4-5cm. Thus, our small 5mm of length adjustment with a crank that is not grossly disproportionate to leg length is likely going to have a net effect on maximal power that is well under 1%. Trading a fraction of a percentage of maximal power for adding a few more key muscle groups into the equation, encouraging high cadence and reducing joint load is a good trade for many riders. You could even think of this as the difference between trying to address sustainable power versus just chasing maximal power.

          Hope this helps.

  • Nick Wimpney

    Shorter cranks give an effectively higher climbing gear, not lower as you state. Also, while it’s true that many riders may benefit from shorter cranks, some long legged riders may have an easier time with longer ones as well. The force required at a given cadence and power output is lower (though there is more range of motion and foot-speed) I’m pretty sure that the change from 175mm to 180mm on my road bike made me faster, and feels better on my knees, especially when sprinting. I seem to be able to spin just as fast, even with the long cranks.

    • Ian

      You are correct on all counts Nick. I used the word “effectively” to mean that a shorter crank creates the sensation of lower gearing for many riders as they pass through the “dead spots” in the stroke faster. The words “lower gear” were poorly chosen and incorrect. Thank you for pointing that out – the article has been updated accordingly.

      You are right that shorter cranks may not be for everyone – the extremes (tall and short) often get missed in exchange for servicing the average. Your anecdotal observations on your knees feeling better with longer arms shows that there is rarely one universal “solution” when it comes to bike set-up. I suspect that, partially because you likely rode proportionately short cranks for years (before you got your 180), you have a pretty well developed/smooth stroke that is active in the transition portions between power and recovery phase. Thus a change to a shorter arm wouldn’t have done much for helping you access already developed muscle patterns and you preferred the additional leverage of the longer arm through the power phase. What type of cadence do you tend to ride?

      Riders on disproportionately long cranks have a more limiting challenge. Riding disproportionately long cranks from day one of your riding life frequently makes developing a higher cadence and active muscle patterns at the top and the bottom of the stroke quite difficult. This can create a tendency to exaggerate joint moments and singular parts of the pedal phase. Shorter cranks directly address this issue and allows these riders to finally feel like they can access more muscles and spin better.

      Thanks for the great comments!

      • Nick Wimpney

        I ride with quite a high cadence in general. Usually around 90-95 RPM, and up in the 125-130 range when I sprint. If I had to guess, I think the longer cranks just let me put more power into the useful range of the stroke, as opposed to on the 175mm cranks, or the 170mm I have on my track bike, I feel like I’m still pushing down too late into the stroke and bouncing myself upward.
        It’s admittedly a fairly subtle difference, but we’re only talking about 5mm of difference, and I’m quite tall, and with long legs for my height(194cm, 1000mm inseam), so I expect my ideal crank length is likely a bit longer yet.

        I’ve just found it strange how the logic seems to work on most bike fitting blogs, etc. There seems to be a general consensus that short people are riding cranks too long for them, average height males are probably around the right length, and tall people are probably fine with average cranks too.

        Sure, it works, but is it best? Not likely.

        • Ian

          You definitely fall well out of the “average length” when it comes to leg length/height. You are right that even longer cranks may feel even better to you. This being said, I suspect that riding on what may be considered proportionately short cranks helped you develop what sounds like a pretty refined pedal stroke. As you implied, biomechanically, the biggest thing that crank length does is play a role in muscle recruitment options and favoring certain portions of the stroke. Longer crankarms favor a different portion of the stroke than shorter lengths.

          There is not much research that I am aware of that shows direct benefit to longer cranks or how to relate leg length to crank length. Everything is pretty anecdotal. Meanwhile, there is the research that shows that even fairly short lengths don’t compromise power across the leg length spectrum. It would be great if there was a joint moment study done on taller riders across a variety of crank lengths so that there might be greater clarity when it comes to the biomechanical loads. As it is, we tend to size road cranks based on what the rider is experiencing, what muscles we want to try to encourage and general proportion.

          In the case of this article on mountain bike cranks, there are a host of non-biomechanical reasons why shorter cranks on many mountain bikes make sense. I’m around 5’7″ and I hit my pedals riding 170 cranks on the full-suspension bike I ride most frequently at least once a ride. Bottom bracket drop doesn’t change on many FS MTB frames based on size and thus riding 180mm cranks may make sense biomechanically for some tall riders, but functionally they would be close to impossible on many bikes/trails. This functional aspect is why I think that the MTB world should consider a crank length below 175 as the standard bearer.

          Thanks again for the comments and there is clearly still research for those in cycling related academia to pursue when it comes to crank length.

  • Olivia

    Can’t shorter cranks help with hip impingement? I have some impingement on my right side, whereby by hip externally rotates at the top of the pedal stroke to compensate. Or is the benefit eliminated as you have to lower your seat anyway. Thank you

    • Ian

      From a fit perspective, shorter cranks are one of the more effective things you can do to reduce hip impingement. This is actually where the concept of shorter cranks really gained ground – in triathlon aero fitting where the shorter crank impinged the hip less and thus allowed the rider to go lower. Based upon what you have said you are experiencing, a shorter crank would be a worthwhile investment for you.

  • Bill

    I’m 198cm tall. I’m concerned about a mtn bike trend to steeper seat tube angles. Manufacturers are chasing longer reaches but maintaining the same effective top tube lengths. So a rider with a long leg is now pushing the knee further forward over the crank end. My knees hurt already on a xxl fuse frame. This will only be worse with these types of frame changes. dropper posts which are common today, work best when centering a seat over the working angle. Thoughts? Also why aren’t more manufacturers extending rear chainstays on larger frames. It seems ludicrous to see the same distances from xs to xxl?

    • Ian

      Hi Bill,
      In our fit studio, we haven’t seen much of a correlation between seat tube angle and rider height. However, you are right that all riders should be concerned about finding a bike that will support their saddle and riding position correctly – thus why we take the fit first approach to bike selection. With dropper posts and bike geometry in general, riders of your height will find that many bikes and some stock seatposts are likely not a good match for you (or your knees). One reason we carry brands like Ellsworth is that the stack and reach of some of their models is bigger than many other brands.

      I haven’t seen much information on the correlation between rider size and chainstay length, but one reason why there likely isn’t variety in stay length has to do with the price of manufacturing multiple rear triangles.

  • Lisa Saunders

    I switched to 145cm on my road bike due to knee arthritis (5’8″) and my fitness and speed have improved while keeping my joints happy thanks to a fitwerx fit by Dean Phillips.

    • Ian

      Thanks for working with us Lisa and glad your fit and changes helped your joints. As you mentioned, shorter cranks tend to put less strain in joints in general.

  • Brian Nystrom

    I think it’s important to point out that not everyone will benefit from shorter MTB cranks. Taller riders who use longer cranks on the road are one example. Matching your MTB crank length to your road crank length (assuming the latter is optimal) is a good idea, as it eliminates the need for adaptation when switching bikes.

    • Ian

      Hi Brian,

      Thanks for the comments and thoughts. I think what you said about matching optimal length is a good point. I don’t think the article stated that short cranks were immediately beneficial to everyone, but it touches on the point that the way crank length and rider height have historically been correlated is not what it has been made out to be from a power perspective. From a power perspective, regardless of rider height, the research shows that there is little to no maximal power difference across a wide range of crank lengths – people can train their muscles to produce power a number of different ways. However, from a biomechanical perspective, what crank length affects is the ease of access you have to specific muscle groups through the stroke. If you have been riding 180mm arms for years, 165mm could feel weak and slow initially, but this is more a reaction to an effective change in gearing and unconditioned muscle activation than the length not being optimal. Once muscle adaptation has happened, quality power can be produced across a wide array of crank lengths. In many instances, and for triathlon and TT in particular, we’ve put riders well over 6′ on 165mm and 170mm cranks and had it improve their comfort and performance. “Optimal” really depends on what you are trying to achieve when it comes to muscle recruitment and joint load. Going longer tends to bias the front of the stroke more and going shorter tends to help riders transition through the top and bottom more actively. This link offers more detailed information on some of the findings.

      Based on the muscle adaptation potential some taller riders may want to consider a shorter crank on their mountain bike because bigger bikes usually don’t have any more ground clearance than smaller bikes.

      Keep on riding and thanks for taking the time to post.

  • Allison Murray

    As always, an excellent article with terrific information explained in a thoughtful manner. I always learn something from Ian.

    • Ian

      Thanks for reading Allison!

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