Should You Change Crank Length?

Without launching straight into a rant about a subject that has been the point of what I’d call  ‘enthusiastic’ debate amongst fitters, bike manufacturers and riders alike in recent years, I’d like to go over some disclosures; these are my own personal views, arrived at through years of riding all kinds of bikes, through various stages of fitness / injury and having performed close to 1000 bike fits for people with varying degrees of body functionality on many different types of bikes. With that disclosure out of the way, let’s talk about crank length…

Why Too High Feels ‘Normal’

There are many theories as to how to arrive at the ”optimal” crank length ranging from the inseam (cm) x 0.216 method to ”I’ve always ridden 172.5mm so why would I change it?”

One of the most common things we notice in the studio is that most people tend to ride with their saddle on the higher side of optimal (or sometimes, even on the higher side of sub-optimal!). Cool story bro, that’s why people come for a bike fit; to sort that kind of thing out! But why? Why is it far more common to see a saddle that’s too high as opposed to too low? Here’s a theory…

Bike riding is weird – from an evolutionary standpoint, we’ve refined the human ‘design’, for want of a better term, to do upright things; to run (the most natural expression of human movement IMHO), walk, lift heavy stuff (don’t get us started on that!)… you get the picture – primal stuff. That’s one of the many things that sets us bipedal humans apart from the rest of the animal kingdom. When we run, we have this amazing triple extension of our hip, knee and ankle as we enter the toe-off phase of our gait (if you want an example of what this should look like, watch Eliud Kipchoge in full flight). 

Eliud Kipchoge demonstrating triple extension of the hip, knee and ankle

When we ride bikes however, we’re in a hunched over, compressed position that somewhat restricts this natural instinct to extend our limbs. Kind of like when we spend 9+ hours per day at our desks, and we all know how bad that is for us! 

Sorry guys, cycling is just more sitting…

The obvious answer? Raise the saddle! By raising the saddle height, we can further extend our legs, reduce compression in our hips at the top of the pedal stroke and all of our natural instincts around how we want to move will be satisfied, right? Maybe… or maybe not. We might have solved one problem and potentially created more, if we’ve gone too far.

Making Problems For Ourselves

Whilst we now FEEL more open and ‘natural’, with a higher seat height, we may have also created some, or at worst, all of the following problems:

– A potential reduction in pelvic symmetry and stability on the saddle (rocking & rolling hips!).

– Lower levels of overall saddle comfort (excessive pressure from saddle pushing up into you).

– A likely loss in power / pedalling efficiency, increasing dead spots at the bottom of the pedal stroke.

– Increased plantar flexion (toe pointing) at the bottom of the pedal stroke to compensate for the additional distance to the bottom of the pedal stroke.

– A likely increase in bodily asymmetry – we’re all wonky by default… but the body will ‘save’ one side of the other.

– Greater pressure on the hands, arms and shoulders as the rider braces themselves against the handlebars.

– Greater stress on the knee and lower leg joints.

The list can (and does!) go on…

I Thought This Was About Cranks!

So, what’s the relevance between all of the above and the length of your cranks? Well, it’s complicated.

In short, to power a bicycle, a complex system of levers need to be engaged to apply human generated force through the pedals that the bike then converts into forward motion. A wonderful system designed by our Victorian forefathers. Splendid. Some levers are attached to the bike (cranks, chainrings, cassette, chain etc) and some are attached to our bodies. The levers attached to the bicycle can be adjusted and it’s all relatively simple stuff – gearing can be changed, crank length can be altered to achieve desired outcomes (climbing mountains / time trialling along the A414 on a Wednesday evening etc), and we generally know what the outcomes of altering the ”leverage” at certain points of the bike will be. 

The human levers – the musculoskeletal system, is a much more fickle and complex beast. How long your legs are / your inseam measurement often is not a reliable way at all to really find out what crank length may be optimal for you. The range of motion through your hamstrings or how tight your hip flexors are for instance might give better insight into what may work better for a certain individual.

Thank you to the Victorians for inventing the diamond shaped bike frame & the body reduced to ‘levers’ is far too simplistic

We need to consider how a rider actually moves and what their limitations in functionality might be to make better decisions surrounding not only crank length, but their bike position holistically.  A rider who is 190cm tall with a huge inseam measurement, but with limited hip and hamstring mobility might actually be better off with a shorter crank length compared with the ”industry standard” 175mm, if it allows that rider to pedal the bike more efficiently, with less postural stress.

”But, I’ll lose power if I switch to shorter cranks!”

Nope, you won’t. A longer crank doesn’t necessarily mean ”more performance”. Besides the case for a potential increase in more efficient bodily function on the bike, longer cranks don’t directly equate to more power

Pressure on the pedal x crank length = torque
Torque x RPM (cadence) = power

Torque alone and the ability to generate power are different and can have greater levels of importance in different riding situations. 

For a World Cup level XC MTB racer, generating sufficient torque is important, especially when climbing very steep and technical terrain where having changing gear under very high load would mean a loss in traction or, at worst, an exploding rear derailleur. Having more torque available helps in this situation to get the rider over a particular piece of terrain without loss in traction or having to make an unnecessary gear change. 

For submaximal cycling (what the vast majority of us actually do) on bikes with gears, the ability to generate huge amounts of torque isn’t as important, as we can make subtle alterations to the torque being put through the system by changing gear to overcome the terrain that we’re riding.

The Math

Here’s where the rubber really meets the road. To travel at the same speed in the same gear, a rider will require less effort to maintain the same foot speed when riding a shorter crank as opposed to a longer one. This is down to the reduction in the distance the foot has to travel to complete one revolution of the pedals. The longer crank will require greater input from the rider to achieve the same foot speed, as it has a greater distance to travel. Another way to think of this would be two riders riding around the velodrome. One on the black line at the bottom of the track and one on the blue line further up the banking. The rider further up the track has to ride with greater foot speed (read; more effort) to match the rider at the bottom of the track to cover the same distance in the same amount of time.

Shorter (than average) Cranks Solve Many Problems

Crank length can also be a useful tool to help alleviate an array of discomforts and suboptimal movement patterns on a bike for all kinds of riders. The bike is a symmetrical object, humans are certainly not symmetrical but, we can strive for better symmetry! 

One of the most common things we see in the studio is an excessive pelvic rock when pedalling, whereby a rider hitches their pelvis (usually more on one side) as a compensation for something in the complex system of levers that isn’t allowing for efficient movement of the body. Commonly, this is a lack of mobility /capacity somewhere in the body to deal with the level of compression during peak flexion at the knee (i.e. the top of the pedal stroke) forced by the length of the crank. This can create a bias towards one side (usually the more dominant side for that particular individual) creating at best an imbalanced / not very efficient pedal stroke and at worst, a whole heap of other issues not limited to those that we mentioned earlier on.

By shortening the length of the crank and making the necessary adjustments to the saddle position (the length you take away from the crank needs to be put back into the system, so the saddle height needs to be raised at the same time – see below), the body doesn’t have to deal with as much compression at the hip when the knee is in peak flexion. This creates less postural stress in the body and as a result, very often a more stable position on the saddle and the pedals. The other way to think of this is like stepping up onto a box… you have to step up onto a box and back down to the ground again consecutively for an hour or two, but there are two boxes; a tall one and a short one and you can choose which box to use to perform this task. Which one are you taking? The short one, of course!

Superb illustration of how different cranks lengths affect your hip angle @appleman – check these guys out for a really deep dive into cranks!

Cranks For Triathletes

Another application for shorter cranks that can have great potential benefits is in a triathlon / TT context. A shorter crank may allow for a more aerodynamic/aggressive position on the bike, whilst also maintaining stability and protecting the hip flexors from taking a beating in the process. It could not only unlock some pretty hefty cycling gains, but it could also have a potentially HUGE positive impact for your running too. And we all know it’s a bike for show, run for dough…

Cranks For Shorter Riders

Finally, size does matter. Although there are no hard and fast rules when choosing crank length based on inseam length / rider height – it is obvious that if you are a shorter 4ft rider and have 175mm cranks, you are going to run into problems at some stage! Currently, shorter riders (often women and juniors) are ‘under-served’ by the bike industry. With limited crank choice being the default, crank length is often not considered as part of a rider’s overall position. Some riders are not even aware there could be a choice! The opposite is also true, very tall riders are also ‘under-served’ by the bike industry in terms of crank length choice.  

Why Are There So Few Options?

Crank length is not a often considered variable because bike manufacturers don’t make a wide range of cranks sizes (compared with the great variety of body shapes out there. Think about all the different saddle options available!) Cranks sized between 165mm – 175mm is the current status quo. 

The landscape is changing slowly with small manufacturers offering some great options (Thank you Appleman, Hope, Croder, Rotor) and recently Shimano introduced a 160mm crank length to its line up, but they’re still super hard to source! Until the big manufacturers start providing more choice as a default, we’re going to be fighting an uphill battle to educate and draw attention to crank choice. And riders will continue to think it is normal for cycling to be uncomfortable, to the extent they may even step away from the sport due to discomfort. 

If you want to read a bit more on this, Nichole Oh recently highlighted crank choice, in her excellent article for Cycling Weekly, about the challenges women and shorter riders face when it comes to setting up their bikes in the face of the status quo.

Don’t Be Your Own Worst Enemy

Once you’re aware that there are different crank length options ranging from 100mm – 200mm out there, then you still have a choice whether or not to change your current setup or not. 

Price is often cited as a reason why cranks are not changed and, yes, they can be pricey components, especially if they have a power meter attached. One of the most difficult conversations we have with riders is trying to convince them to change their crank based power meter because they could benefit from a different crank length. The power of the sunk cost fallacy is strong! 

You have to look at the big picture. If you were driving down a road in the wrong direction, then found out the right direction to go in, would you continue driving in the wrong direction just because you have already spent a good amount of time and effort going in that direction?

If there is a biomechanical advantage to getting shorter cranks, simply sell your power meter, and get a new one! 

We make around 10,000 pedal strokes an hour. If changing to shorter cranks produces 10,000 better pedal strokes, would you make the change? Of course you would! Remember you are investing in your HEALTH and your RIDING for the long term.

Appleman fit cranks go down to 100mm!

And Finally…

As with everything bike fit related however, there are no hard and fast rules of thumb or gross generalisations that we can take as gospel. You are an experiment of one and it’s important that you find out what works best for you. Shorter cranks might not be necessary for you. You might not notice a difference, or you might need that extra torque for a hilly MTB XC or Cyclocross race in the mud. What I will say though, is that if you’re having some issues on the bike and you don’t know what crank length might be best for you, I would strongly urge you to find out.

Words by: (one ‘t’) Mat

Phew! If you’ve made it to the end of this article, thank you! We really appreciate your time and hope this was useful for you.

If you’re ready to explore what could be the best crank length for you, hit the link below to find out more about your Fit Before You Buy service.

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