Your Guide to Crank Length

A blend of science and practical advice about crank length.

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Crank length. So hot right now 🔥

I get asked about crank length almost daily, in particular shorter cranks, because it seems to be everywhere on social media and cycling magazines at the moment, often portrayed as a new concept. Um… spoiler alert - It’s not! To be honest, I sometimes really want to roll my eyes and sigh. I usually jokingly say that “2008 called and asked for it’s crank debate back”, followed by saying ‘it depends’, proceeding to bore the poor athlete who asked with far too much information about the pros, cons, myths, stories and then finally the only thing they really wanted to know - A simple yes or no answer to whether they should change their crank length or not...

Let me backtrack to 2008 so you have some of the background… If you read the article about how I got started as a bike fitter, you’ll know that in 2008, I started working with several triathletes training at the national triathlon training center in Victoria. After the Beijing Olympics, I also started fitting a few Olympians (draft legal triathlon) and that is where the crank length discussion started, as a conversation with their coach. As a result of that, I was doing a lot of reading, sorting through every biomechanics and physiology paper I could find on crank length. In early 2009, a two time medalist, three time Olympian (at the time) scheduled a fitting appointment with me. I packed up my gear for a house call bike fit and no sooner than a few minutes after I arrived, I got asked for my opinion about crank length for triathlon. I felt like this was a make it or break it moment, as my career was just getting started - If I gave him an answer that did not resonate, I might mess up a great career opportunity… I guess my answers made sense because I continued working with him for the remainder of the Olympic cycle, up to the London Olympics (he retired after). Phew, right? In case you are wondering, he used shorter cranks than what was typical at the time.

The crank length discussion is one that I have been having with athletes for the better part of 14-15 years, in particular on shorter cranks, so when someone tells me that going for shorter cranks is a new concept, I find it really hard not to roll my eyes.

I have many crank length related stories, but we don’t have all day and there is a lot of ground to cover here, so I will save those for another time.

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Crank Length Introduction

Cranks are measured from the center of pedal axle to center of bottom bracket axle. If you want to know what crank length your bike has, just look for the number on the inside of the crank arm. Pro tip - Always check both sides. I have seen two different lengths on bikes on several cases (not on purpose), which resulted in disasters.

Cranks are usually somewhat proportional to the size of the bike (in most cases) - Smaller bikes typically come with shorter cranks and the crank length increases with the size of the bike. In the past, it was pretty much impossible finding cranks shorter than 170 on even the smallest bikes, but now many brands equip their smaller bikes with 165 cranks, with the largest bikes coming with 175 cranks.

To be honest, I would be a much happier bike fitter if brands allowed the crank length to be customized when a rider buys the bike… I suppose that’s the beauty of building a bike from the frame up!

On the surface, the crank arm is a lever and as such, any increase in length can potentially provide the rider using it extra leverage. Of course, this is a simplified approach that does not hold in practice because of the human joints that are involved in driving each side of the crankset through extension and flexion.

Below is a bit of science to kick things off, with references at the very end of this article (including papers not directly mentioned but used to write this post). Lets start by going all the way back to 1983, when Inbar et al (4) measured the mean and peak power for maximal efforts using crank lengths from 125mm to 225mm. They concluded that 165mm cranks could be the optimal ones for both mean and peak power, but the differences between 150mm to 200mm were not significant.

So what about metabolic cost of cycling and crank length? In 2002, McDaniel et al (5) showed that switching between crank lengths of 145, 170 and 195 did not change the metabolic cost per se, but that the metabolic cost was dependent on power output and cadence.

In 2011, a study by Martin (2) demonstrated that changes between cranks ranging from 150-190 did not compromise maximal power or change the relative joint power contribution at the hip, knee and ankle. It is important however to control pedaling rate (ie. cadence), as when cadence is constant across all crank length, the longer ones can result in less relative knee flexion power and more relative hip extension power.

In 2017, Ferrer-Roca et al (3) looked into metabolic cost and pedaling technique with crank lengths ±5mm preferred crank length. There was no significant effect on heart rate and metabolic efficiency between crank lengths, but longer cranks increased flexion and the range of movement required at the hip and knee (but not ankle), which was not noticeable with the shorter cranks.

There is one specific circumstance where a longer crank will develop more speed compared with a shorter crank - A standing start with a fixed gear, over a very short distance, AKA sprints under 200m. I am assuming this does not apply to 99% of you currently reading this, or almost all the athletes I work with.

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Why would you want to change your crank length?

If changing your crank length results in little difference to power output, the obvious question is: Why bother?!

Cycling is highly repetitive for long durations, at various loads, using a highly symmetrical machine (the bike) powered by a highly asymmetrical machine (the human body). The proponents of shorter crank length claim that they could:

• Enable a more aerodynamic position, in particular for TT events

• Help with a smoother pedal stroke, hip stability & cadence

• Help with lower back, hip and knee pain

• Improved run off the bike for triathletes (both long course & draft legal events)

• There might be improvement with saddle comfort

• Technical considerations like toe overlap, off road riding considerations, bike geometry, etc

Big claims, right?! Lets break each of them down in (a lot) more detail and explore some of the cons of going shorter too… If you are a free subscriber or a visitor here (welcome!), feel free to get a trial subscription to continue reading, as I get into more detail about crank length as it relates to aerodynamics, pedal stroke, power, cadence, hip stability, velocity, technical stuff, how to decide what is right for you and more! If you are already a paid subscriber, carry on…

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Enable a more aerodynamic position

Going to a shorter crank could allow you to ride at a lower back angle which minimizes frontal surface area, improving aerodynamics. Obviously, if your knees do not come up as high (due to a more open hip angle), the increased angle between the femur and the tibia can reduce the load on the knee, therefore potentially reducing the risk of injury, given the fore-aft position of the saddle is appropriate for the rider. In addition, shorter cranks may facilitate a more open hip angle, helping with getting into a more aggressive position and less restriction through the top of the pedal stroke = Can produce more power in practice, with less fatigue.

This is more important of a consideration for TT and Triathlon positions vs road, assuming you are on the right bike for you and your goals.

A smoother pedal stroke, hip stability, power & cadence

Power: A shorter crank will not increase your power output, but it can be used to reduce restriction through the top of the pedal stroke by opening up a potentially impinged hip angle and/or reducing knee flexion. If we reduce restriction, then power output can increase and / or be maintained for longer durations.

Cadence - I once worked with a high performance Ironman athlete and reduced his crank length by 10mm, then adjusted the overall position accordingly. The conversation after he returned from a training camp went something like this:

• Him: I rode the Ironman course faster than ever before with less effort and was comfortable. But I don’t like the shorter cranks

• Me: ??? But if you were faster and more comfortable, what’s the problem?

• Him: My cadence was higher, I didn’t like that

• Me: Did you change gears to reduce your cadence?

• Him: No. I’ll go back to the longer cranks so my cadence stays the same

• Me: WTF 🤯

Cadence will increase as a result of the smaller circumference. Do you struggle pedaling at higher rpms? Changing your crank length could help, particularly up hills, after taking into account gear ratio, of course. On the flip side, if cadence is not an issue for you, you will need to adjust your gearing if you go for a shorter crank length.

Hip stability - Most people notice vertical hip movement, but lateral hip movement is often an overlooked issue affecting hip stability on the saddle, leading to saddle discomfort and lower back issues, which is often caused by cranks that are too long, especially in more aggressive positions like TT and triathlon. This is also a consideration when the rider has trouble getting their legs over the pedals, in particular through the top of the pedal stroke, which could happen when there is hip impingement (reasons for the hip impingement will vary). Hip stability deserves a post on its own, so I’ll just add it to the list.

It has been suggested that newer cyclists might be able to ride with improved economy and higher power when using a shorter crank length. I suspect that is related to the points above regarding cadence and hip stability.

Help with lower back, hip and knee pain

Comfort: A shorter crank length reduces range of motion at the knee (extension and flexion), hips, and low back.

It helps with hip restriction in particular, so you can reduce the load on the area, as well as reducing fatigue. This includes the lower back, glutes and hip flexors. Everything often feels more fluid and smoother, helping to facilitated better knee alignment.

Running off the bike

This is for the triathletes in the bunch. Back to the considerations around open hip angles and reducing forces around the hip flexors and lower back, shorter cranks can help as the body transitions from being hunched over the bike to a tall running position. It also helps making sure there is minimal restriction with leg extension needed for running, especially when there is a need to run very fast off the bike (ie. draft legal events). Shorter cranks have been a massive help in short course triathlon due to the rules of competition regarding the bike itself (road bike, saddle 5cm behind the BB, etc), as well as the typical courses that often include lots of corners, U turns and the need to accelerate A LOT throughout the bike part and then still run fast afterwards.

Saddle comfort

Peak pressure on the saddle could improve - I have noticed that extra pressure on the saddle often results from tightness around the hips and if shortening the crank can help with that, then potentially there will be improvement on the saddle comfort end of things. As a result of decreased peak pressure on the saddle, if there are saddle sore issues, those might get reduced or resolved. Saddle comfort involves MANY factors that need to be considered, so we will get into that another time.

Technical + other considerations

Technical stuff - More clearance for cornering and obstacles - applicable for off road, crits, cross racing and anything where a high torque is required. Shorter is often better for accelerations and turnover.

Off road riding - A 2010 study (6) found that riders were able to reach their peak power faster on shorter cranks, meaning that in the real world, they might be able to clean an obstacle better. Pedal strikes due to roots, rocks, etc can be a common complaint and shorter cranks could help with that. I suspect that the same will apply to other cycling disciplines.

For the ever growing gravel crowd out there (myself included), when you are on a steep climb on loose gravel, you typically need to stay in the saddle and get lower on the front end to maintain traction (different than road). This can place more load on the hips and lower back, as well as the knees. A shorter crank could definitely help with that! See the article on gravel vs road bike fit for more info.

Toe overlap - Typically not an issue but can be more of a consideration for smaller bikes. Shorter cranks can help prevent or reduce it.

Additional factors that could affect crank length selection include:

• Cleat position - For example, cleats that are set quite far back towards the arch will affect both the saddle height and fore-aft position and could lead to the need for shorter cranks (and / or a more forward saddle position)

• Bike geometry - For example, putting long cranks on a bike with a low bottom bracket can cause issues with pedal strike while cornering. See additional comments on this in the ‘con’ section.

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Should I change my crank length? How do I choose the length?

Remember that article about carbohydrate intake from last summer? We discussed how using wording like high carb and low carb doesn’t make sense and instead carb appropriate is better. Well, cranks are no different! I want your crank length to be appropriate to YOU.

Yes, there is a very good chance you could benefit from a shorter crank, but maybe your crank length is already appropriate for your goals and needs? Maybe there is little benefit to spending the resources (time and money) to change it? Note that there is a much lesser chance you’ll need to go for a longer crank than what comes on your bike, but that could happens too, in rare cases.

Lets remember that short is a relative term. If we think of things in terms of saddle height : crank length, lets compare a triathlete (athlete #1) who has a saddle height of 860 with 172.5 cranks to another triathlete (athlete #2) with a saddle height of 670 with 165 cranks. Most would assume that athlete #2 has a ‘better’ crank length because its shorter, but if we break it down, athlete #2 will need to be on ~135 cranks for a similar saddle height : crank length ratio as athlete #1… This is simply to highlight that crank length is relative and depends on many factors.

Clues that you might need shorter cranks:

• You struggle to get over the top of the pedal stroke, placing a lot of load on the hip flexors, lower back and knees

• Knee alignment issues at the top of the pedal stroke (knee tracking outwards) might mean there is an inability to engage muscles properly and there is restriction leading to this compensation pattern. That said, there are certainly additional bike fit related fixes to explore first.

• Those with chronic hip and lower back issues, very tight hamstrings and hip flexors could potentially benefit from going shorter. Bike geometry comes into play here too, as well as a bike fit, not just assuming the cranks will solve all your problems.

For the most part, someone with experience should assess your goals, injury history, riding discipline and needs, how your body moved off and on the bike, including range of motion and strength. Based on all the information available, the most appropriate crank length for you can be determined. And if the fitter has a fit bike, you can try a wide range of cranks before making a decision and spending the money.

Keep in mind that like anything else, this is dynamic and not set in stone. What is optimal for an individual at one point in time might not be the same months or years down the road, with aging, changes to range of motion, varied goals, different bikes and changes to fitness level.

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Cons of shorter cranks

No, maybe you do not need to go shorter… One size never fits all. Just because many people might want to consider going for a shorter crank length for all the reasons we discussed above, it certainly does not mean that it is always the case! Admittedly, it is more rare that I need to get someone on longer cranks than what came stock on their bike. It typically happens when someone decided to go for an excessively short crank (because the internet and their friends told them to), subsequently causing issues with the fit as a whole.

I mean, someone who is 6’3 should probably not ride 160 cranks, especially when riding a race bike but not having a lot of riding experience, as well as showing poor mobility and the inability to ride in a more aggressive position. Yes, this is a real example… I know we said that shorter cranks can help with back issues, but think of it as a reverse U curve. there is a point of diminishing returns and even potential problems if you have gone too far.

We need to think in terms of appropriate, rather than sweeping statements across the board without critical thinking on a case by case basis.

The cons of going shorter if that is not needed:

• Weight distribution (front and back) on the bike can be negatively affected if the cranks are too short, causing issues with bike handling.

• Shortening the cranks often leads to an increase in drop between the saddle and handlebars and could also lead to reach issues (to the handlebars). Sometimes that is positive, but on the flip side - Can you hold that more aggressive position? Can modifications be made to the bike without compromising the bike’s handling characteristics in order to control this variable? Because if the goal is to reduce the load on the back and then the drop to the handlebars is more than you can handle, that could backfire and be painful, ineffective and expensive.

• The cost of changing the crank could be prohibitive, especially if a power meter is involved. This is better now compared with 10+ years ago when power meters were A LOT more expensive (and there were a lot less options), but it is still an important consideration.

If the only goal is to open up the hip angle, there are other ways of doing that from a fitting stand point - shortening the cranks is not always the answer and should not necessarily be the first resort.

If you decide to change the crank length, shorter or longer, please do not just swap and go ride - You need to adjust the fit, and while it is not brain surgery, it is NOT as easy as shorter cranks by 5mm so saddle goes up by 5mm. You will need to adjust the saddle height, the fore-aft position and potentially the handlebar height and / or reach, because changing one aspect of the fit has a dominos effects on everything else. Its all connected.

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Bike Specific crank length

Lets say you ride a 170 crank on your road bike. Should you ride the same length on your TT or tri bike? How about your gravel bike? Track bike? Obviously, the answer depends on many factors, but for the most part, things usually stay similar with the exception of track and TT / Tri bikes, where you will very likely go shorter than your road or gravel bike.

For reference, both my gravel bike and road bike have 165mm cranks (I’m 5’5).

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What is available on the market right now?

There are a lot of brands making cranks out there… If you are interested in what is available on the marker currently, you are in luck as I did the leg work for you!

The information in the link below is as of January 2023. Thing will likely change down the road as more brands are starting to manufacture shorter cranks... I Keep track on what is available on the market for my day to day work with athletes, so I will update the linked pages as things change.

You can get cranks as short as 120 (!) and as long as over 200 from a variety of brands and within each brand, there is variation of what is available depending on the model. This is not a complete list, but one that includes the major players and a few outliers making things for those who need something out of the ‘norm’.

A few important notes:

• Check in with your mechanic to ensure compatibility before buying.

• Definitely check in with your bike fitter first, and schedule a session with him/her after making the change, too!

• Power meter considerations - Some of the models above come in a power meter option and/or have compatibility with various power meter brands. If you already have a crank based power meter or plan on using one, double check availability and compatibility. Of course, if needed you can consider using a pedal based power meter.

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References

(Sorry, I can’t share full text articles as I get them through a paid database)

1. BARRATT, P., MARTIN, J., ELMER, S., & KORFF, T. (2016). Effects of Pedal Speed and Crank Length on Pedaling Mechanics during Submaximal Cycling. Medicine & Science in Sports & Exercise, 48(4), 705-713.

2. MARTIN, J. (2011). Effect of Crank Length on Joint-Specific Power during Maximal Cycling. Medicine & Science in Sports & Exercise, 43(9), 1689-1697.

3. Ventura Ferrer-Roca, Víctor Rivero-Palomo, Ana Ogueta-Alday, José A. Rodríguez-Marroyo & Juan García-López (2017) Acute effects of small changes in crank length on gross efficiency and pedalling technique during submaximal cycling, Journal of Sports Sciences, 35:14, 1328-1335, DOI: 10.1080/02640414.2016.1215490

4. OMRI INBAR, RAFFY DOTAN, THOMAS TROSUL & ZEEV DVIR (1983) The effect of bicycle crank-length variation upon power performance, Ergonomics, 26:12, 1139-1146, DOI: 10.1080/00140138308963449

5. Determinants of metabolic cost during submaximal cycling

   J. McDaniel, J. L. Durstine, G. A. Hand, and J. C. Martin

   Journal of Applied Physiology 2002 93:3, 823-828

6. Macdermid, P., & Edwards, A. (2009). Influence of crank length on cycle ergometry performance of well-trained female cross-country mountain bike athletes. European Journal of Applied Physiology, 108(1), 177-182.

7. Burrus BM, Armendariz J, Moscicki BM. Cycling with Short Crank Lengths Improved Economy in Novices. Int J Exerc Sci. 2021 Sep 1;14(1):1123-1137. PMID: 35096228; PMCID: PMC8758175.

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I hope you found this article valuable and an interesting. I would also love to hear your thoughts, so feel free to comment below and share this post with others!