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  • Writer's pictureDavid Wadsworth

Top Reasons to Move to Shorter Cranks: Pogačar Already Has

Pro Peloton Trends: Shorter Cranks

Tadej Pogačar changed to 165mm cranks on his road bike this season.  For an already successful rider who started out on 172.5mm cranks, there must be some compelling reasons why he deliberately made such a change.  Let’s take a deep dive into selecting crank length, as it’s relevant for every riders own bike fit and performance.

 

The first thing to note is that shorter cranks haven’t hurt Pogačar's performance one bit.  At the time of writing he has dominated and won every single race he has entered so far this season, with one exception being Milan San Remo where he came 3rd (hardly a bad result!).  I have been selectively recommending shorter cranks lengths for years based on various individual characteristics and requirements of individual riders.  So, what things might indicate a need to switch to shorter cranks?


1.      Leg Length or Proportionately Short Legs

This might sound obvious, but if you have long legs, you are likely to benefit from longer cranks, and if you have short legs those longer cranks may well push your joints too far and lead to problems.  Unfortunately, new bikes tend to come with a very narrow range of cranks (usually 170mm, 172.5mm, or 175mm).  Whilst most manufacturers offer at least 6 frame sizes, none offer 6 proportionately matched crank lengths.  In fact, one year a major bike manufacturer (who shall remain nameless) applied 170mm cranks to every frame size, obviously to save themselves money on a bulk buy discount (consumers didn’t see a reduction in their purchase cost!).

 

So, if you have shorter legs or proportionately short legs (for example with a long torso), then shorter cranks make a lot of sense. Without doubt all junior cyclists should start on cranks substantially shorter than 170mm (unless maybe your child has the legs of a Giraffe!).

 

2.      Musculoskeletal limitations: tight hips

An incredibly common reason I recommend shorter cranks to riders is a limitation of hip motion.  The hips undergo the largest amount of motion in the pedalling stroke, specifically into flexion (in other words knee to chest movement).  If you have tight gluteal or hamstring muscles, or a bony block to hip flexion (such as hip impingement or retroverted hips) then short cranks are likely to be of significant benefit.  If the cranks are too long there is likely to be a lot of compensatory movement occurring such as knees splaying out wide or the pelvis rocking and low back rounding, leading to things like back pain and saddle sores.

 

3.      Hip or Knee Injuries / Pain

Riders with certain knee issues that are aggravated by the repeated flexion motion (bending) that occurs every pedal stroke may benefit from shorter cranks, which reduce the amount of bending required.  The small changes in hip and knee angles and forces are often enough to allow a rider to continue to cycle without pain.  Of interest is that the shorter cranks tend to result in lower peak acceleration of the femur / leg in the pedal stroke, which benefits anyone experiencing overload whether it be the joints (hip and knee) or muscular system.

 

4.      Discipline Specific Needs

Filippo Ganna set a new hour record on 170mm cranks. He is 193cm tall.

Different cycling disciplines obtain clear and unequivocal benefit from selecting different crank lengths when compared to their road bike crank length.  Time triallists and triathletes have been shifting across to shorter cranks in recent years due to clear aerodynamic advantages.  The shorter crank length allows the torso to be lower, reducing frontal cross sectional area and aerodynamic drag.  Triathletes may also find running off the bike easier.  Track cyclists may prefer shorter cranks as they afford faster acceleration in bunch races on their single speed bikes. 




Conversely, in XCM mountain biking,  the seated uphill climbing required is a lower cadence higher torque effort that benefits from a slightly longer crank length, which is why most mountain bikes come fitted with 175mm cranks as standard (to test this try standing and spinning at a high cadence on a loose gravel climb and see how much traction you can get). The more upright torso posture on a mountain bike permits the use of a marginally longer crank, although these days smaller riders can more easily purchase a shorter mountain bike crank that is in proportion to their leg length.

 

5.        Rider Physiology

This may be more controversial and less well validated at this stage by science but consider a lightly built rider (perhaps a climber) who develops their peak power at high cadence, and due to their low muscle mass has limited ability to produce high torque.  Often this type of rider is aerobically dominant in terms of their physiology (think lots of slow twitch muscle fibres) and may benefit from a performance perspective by using shorter crank lengths, which make their high cadence pedalling action easier.  In contrast a well-muscled sprint athlete (think fast twitch muscle fibres) who excels at lower cadence high torque efforts, the shorter cranks might not be their best option; rather a crank length in proportion to their leg length (rather than shorter than normal) is a wiser choice. 

 

If you are struggling to picture the effect of crank length on cadence, imagine a clown riding a bike with crazy long cranks.  At the top of the pedal stroke their knee will hit their chest (“closing the hip angle” resulting in substantial power loss), they will have to sit more upright or round their back or make some other compensation for this forced hip and knee flexion. Now imagine trying to turn the really long crank over – it’s going to be slow and hard to do (lots of torque / force required but the cadence will be really low).

 

bicycle crankset depicting forces resulting in power calcuation
Power = torque (crank length) * angular velocity (cadence).

Before anyone says "a shorter crank will cause me to lose power!" let's examine how power is actually calculated. In cycling the power that matters is that which is applied to the pedal via the crank arm. The physics equation is shown in the diagram above. There is a constant in the equation not shown (the rider - whose power is their power irrespective of what cranks they ride!). So shortening the cranks reduces the torque but increases the cadence side of the equation. The net effect = no change on power production (and this has been shown time and again in experiments on real humans since we all obey the laws of physics). A longer crank increases your torque / force but reduces the angular velocity (cadence) again creating a net effect of no power change.


So why did Pogačar make the change?  He rides 165mm cranks on his time trial bike (a discipline specific choice for aerodynamics) and had made the shift from 172.5mm to 170mm on his road bike with success the year before.  Thus, his change to 165mm was a more gradual, considered switch to shorter cranks and informed by his time trial riding position.  He is 176cm (approx. 5”8”) tall, and currently uses a non-offset seat post contributing to a forward position.  All of this results in a more open hip angle (better for power production, breathing and aerodynamics), yet his torso angle isn’t terribly low compared to his professional counterparts (suggestive that Tadej may have somewhat tighter hips and is willing to forego the aerodynamic advantage of the short cranks for the other reasons mentioned).  Certainly, his results speak for themselves! 


If you are a rider who might benefit from shorter cranks but are wondering if they'll really help or not, consider this. In professionally fitting bikes for 20yrs, I’ve yet to meet anyone who made a (sensible) reduction in crank length who said “these are too short and causing problems”.  I can’t say the same for riders trying to ride longer cranks than their leg length, flexibility and cycling goals would suggest is sensible.

 

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