Short vs. Long MTB Cranks | Physical Therapist Perspective

just change chap your backside then I'm about to make you mad than a mosquito and a mannequin Factory let's talk about short Mountain bik [Music] cranks so in case you're thinking about ducking out early let me say out front this is not a sponsored video I didn't have a brand send me a box full of short cranks or is it coming from the perspective of someone that just got their pair of first cranks and I'm going to take them out ride them twice and tell you how much you need short cranks because I've enjoyed them in these two rides for well over a year now I've been running 160 mm trailbike cranks and 155mm ebike cranks more recently I've even been testing out some 155 mm regular trailbike cranks for reference I'm 5'9 with a 31in inseam so from the perspective of being a live long mountain biker I like looking at new products I like looking at things that might help me improve my performance and overall enjoyment and maybe even keep me a little safer on the bike from the perspective of being a doctor of physical therapy I do occasionally look at things through the perspective of biomechanics that is the study of human movement and how forces acting on and from the human body can affect our performance on the bike and things like injury prevention and recovery and so from those two perspectives it's my humble opinion that most mountain bikers and definitely every bike brand should be taking a more critical look at cranklen so consider this if a bike brand released a new bike that had geometry specs and components from 10 years ago we would laugh that brand straight off from the pink bike comment section if a bike brand released a new bike with 20year old standards we would think it's an April Fool's joke and yet pretty much every bigname bike manufact facturer now in 2024 are still shipping sized small medium and large bikes with 170 and 175 mm length cranks that one size fits pretty much everyone based on Antiquated standards approach just doesn't play out with the science or what myself and many others have experienced and that is exactly how I want to break this down I want to briefly look at the science on the topic now I also want to share with you my personal experience and from there you can take it or leave it on short cranks so if we're going to talk about the science of short versus long cranks we'd really like to at least in part go past the opinion piece articles and look at the actual peer-reviewed research in actual scientific journals so the best that we can do is borrow from a handful of studies that have been done utilizing mostly Road bikers always in a lab environment always using clipless pedals these handful of Studies have pretty much been regurgitated now in every article in video before this one and I'm not going to do that but I will summarize them as saying that even if you find them valid and applicable to mountain biking what you're going to find that these studies indicate that pretty much no commercially available crank length offers Superior maximum power output and yes that's even when testing cranks even well below these 155 mm cranks and even when going above the old standard 175 mil cranks pretty much all the studies have found that there's no advantage to Shorter or longer cranks for maximum power output one study that I will mention is a 2021 study that was published in the international Journal of exercise science where they took 14 novice cyclists they had them perform at a 60% V2 Peak what they were testing was the difference between 145 mm Cranks versus 175 mm cranks and they were measuring what they called cycling economy and average power output the higher cycling economy the more efficient they were may come as a surprise that these novice cyclists averaged a higher power output and had higher cycling economy with those 145 mm cranks now this study does have some limitations in that it was a Nova cyclist and it wasn't a lab environment but I would argue that maintaining a 60% effort for 30 minutes could mimic a long Fire Road climb in mountain biking and at least points Us in the direction that there may actually be a slight Advantage toward those shorter crank links and that flies in the face of what is the most common thing to say in a video about short versus long cranks and that is long cranks have more leverage long cranks for more power and BMX well the reality of the situation is what they're generally referring to is torque and certainly torque is force times the length of the purp perpendicular lever arm this case the lever arm is the crank length and assuming that the force that you're able to put into that crank is the same between crank links certainly there will be a little bit more torque in the longer crank arm but there have been Engineers who are much smarter than I am in physics that have quickly explained this away by suggesting that any torque difference that may exist is quickly done away with with a simple gear change maybe even a chain ring swap to a slightly smaller chain ring size additionally torque is not power power is actually measured over time and it is well established that when utilizing a smaller crank arm you're actually going to generally average a few more revolutions per minute with using a longer crank arm which means that you're getting that crank back around to The Sweet Spot where you're actually able to apply Force into it more times in a minute I would also argue that from a biomechanic standpoint I don't think that you're able to put Force into long longer cranks as efficiently as you're able to put Force into shorter cranks so if we'll imagine an imaginary long crank arm situation the longer crank arms bring your knee and your hip into a greater degree of flexion or bend and so as I come around that pedal Revolution and I get back to the 12 or 1:00 position I'm getting to that point in the pedal stroke where I can start to really apply force and in this position with the longer cranks my hip and my knee again are closer to their maximum ranges of motion and that is not an optimal place to generate Force whereas with shorter cranks it's subtle but you do let some of the bend off in your hip and knee and it's getting closer to the middle of the range of motion where both your glutes and your quads are going to be able to demonstrate more Force into those cranks so if you've ever spent any time in the gym doing squatting with an actual weight bar you know that the hardest point in the movement especially if you have a significant amount of weight weight on the bar is when you go to reverse Direction and go back up you know that when you get here closer to the middle of the position you've probably got that movement whipped to me cycling with longer crank arms puts you closer to this more maximally bent hip and knee position whereas cycling with shorter crank arms have you closer to that middle of the range of motion where you're going to be more powerful over a 2 to three hour ride would you rather do 3 hours of full depth squats or would you rather do 3 hours of partial depth squats which do you think would have you feeling more beat up the next day and speaking of deep knee and hip bends even if the power output or the energy expenditure was the exact same among crank links what about your comfort on the bike with longer cranks it is very well established that your hip and your knee go into a significantly deeper Bend or flexion range of motion than shorter cranks and as a physical therapist I want people to have full range of motion I don't even think that it's wrong to exercise within those full ranges of motion but in the case of cycling it is in fact cyclical and it happens over many many repetitions and even for an average weekend warrior style Rider who rides 3 hours per week and they spin at an 80 RPM Cadence that is over 14,000 knee and hip bends in a week and 748 th000 knee and hip bends in a year here if you're a more Avid Rider and you're averaging 10 hours per week that's a whopping 54,000 Revolutions in a week and over 2.8 million knee and hip bends in a year and so while utilizing your full range of motion inherently shouldn't be bad doing it 2.8 million times in the same exact way per year can certainly predispose an individual to an overuse injury shorter cranks are going to predispose you less to an overuse injury in your knee and hip a rider that's comfortable is going to be much more motivated to go and pound some miles and one other thing worth considering and thinking about the biomechanics of shorter cranks is that your stance will become slightly closer together with shorter cranks if you sort of exaggerate it just so that you can see the point you can really extend that stance and then try to twist your body and you'll find that a lot of that movement is trying to come in in your knees and your ankles and you really just don't move move well that way versus if you bring it a little closer together that frees your hips up to be able to rotate a lot more which is pretty important for cornering and so there is an argument that that slightly closer stance with the shorter cranks helps people feel more confident in their maneuvering on the bike and some people even report feeling more stable all right enough about the science let's get down to the meat and potatoes of the issue and that is how does short cranks actually play out here on the trail so today for the sake of experimentation I've actually borrowed a buddy's 165 cranks and then I've got some 155s we're going to do some back toback testing on probably the worst climb that we have here locally it's not a long climb but it is definitely Steep and janky it's hard to keep traction on it I'm going to be keenly interested to see how the power output and the traction FS going from 165s to 155s let's check it out all right first pull with the 165 I know I said I've been running one 60s but I wanted a little wider spread than 160 to 155 woo back my second attempt here on the 165s I don't know if I get underestimated how wet it is today today here's the fourth pole it's the problem I'm having is nice and wet these leaves fifth try 165s it's just too slick it's interesting going back on these 165s after being on 160s definitely feels a little long in the tooth but nothing crazy all [Applause] right you can definitely feel that longer stroke 165's off 155 is on let's try it again all right so quick sort of acclamation spin on the 155s the circles obviously feel shorter it's not insane the difference but you can definitely tell a difference it's uh it's also crazy how much more upright you feel on the bike I actually left the same chain ring immediately what I'm feeling is it feels like you're able to keep it in the power section of each pedal Revolution better that's that's the best way I know to put it it's like you're back around each side of the crank to be able to hammer into them quicker with the short ones actually going to try it's big brother dollar heill couldn't get it with the 155s I'm not [Applause] sure I got it wo I could not get it with the 165s the first try with the 155s nailed it so there you have a rather unscientific but certainly raw and honest back-to-back test here on my local Trails where I pitted 155s against 165 mm cranks on a short burst Hill Climb where you definitely need near maximum power but also a lot of traction out of the bike and I'll be straight I was surprised at how much of a difference I could actually tell between the two especially as it related to how much quicker it seemed like those 15 5S would spin up to near Peak power but also how much smoother the pedal Revolution felt on those 155s which yielded a noticeable Improvement in traction and so I've been able to spend time with these 155s on three different bikes and this is not only further solidified the fact that I'm a short cranks fan but it's actually shifted down what I perceive to be the sweet spot for crank link for me personally to 155 again I love how quickly they seem to spin up I love The Stance f when you're in that standing pedals level position it's a half a cm less likely chance of pedal striking compared to even the 160s that I've been running before in my honest opinion it is that pedals level stance ready position on the bike that will prevent us from just all running 120s a few years from now because the stance may start to creep in and feel a little bit too narrow it's the same reason why I can't just make a blanket statement to recommend 155s to everyone watching this video because taller Riders May certainly start to creep in to too narrow of a stance for what they feel is comfortable but I definitely believe wholeheartedly that our scale of mountain bike crank length does need to shift down with one of the main reasons being one thing that generally doesn't change from extra small to double extra large mountain bikes is the height of the bottom bracket and as you already know modern geometry has gotten lower and this needs to be reconciled in part with shorter cranks we out of the shop here have put multiple Riders well over 6 ft tall on 165 mm cranks and not only have a handful of them reported less knee pain we've not had any negative feedback about how they performed and felt on the bike overall and so my strong but biased opinion is that the top end of the scale could in fact be 165 mm and so I would ask everyone why would you not want to run the shortest possible Crank that you can run while still feeling natural in that pedals level position while enjoying the benefits of quicker spin up a smoother pedal Revolution and decreased pedal strikes so how do you choose which crank length is right for you well I can't answer that question because I don't believe that there is a one- siiz fits-all answer and I certainly don't believe in any of the formulas or tools that are floating around out there because they're not backed by any solid research and they tend to recommend crank links for Toler riders that are way longer than I think are necessary so in the absence of anything truly concrete it'd be wrong for me to give you any definite recommendations what I can say is consider my own experience with a healthy grain of salt for those that are on the taller end of the spectrum or for those that are only marginally curious about short cranks I think you would be quite safe in trying 165s for those of us in the more average or even lower end of the height Spectrum or those that are just dog tired of pedal striking because of their super low slung bike you may very well appreciate crank Links of 160 or shorter certainly if you're anyone that's dealing with a nagging knee hip or maybe even lower back issue shorter cranks could be part of the recipe for you to get rid of that problem so what about swapping chain Rings everybody really wants to drive this one into the ground and my humble opinion it's a little bit overplayed I can actually ride everything with these 155s with the same 32 to chain ring that I used to use on the 170s I do prefer dropping down to a 30 to my recommendation start with the chain ring you have and if you need an easier gear or two in your climbing gears drop down a couple of teeth so sorry this one's definitely been a little longer than my normal videos we're going to cap it up here definitely check out Link in the description below for a YouTube short supplement video If You unsure about which crank link size you need and you're in the South Central Kentucky area swing by summer cycle we'll rent you a set we'll then apply that rental toward the purchase of your own cranks or if you're getting long great with longer cranks keep sending it please consider subscribing to the channel definitely on this one leave a comment below to let everyone know your experience with shorter cranks as always thanks for [Music] watching

Channel: Dr. J MTB

Views: 44,155

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Id: dV-xuw5KFJ0

Length: 17min 52sec (1072 seconds)

Published: Thu Feb 15 2024