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I went from 172.5 to 165mm. I am 5'11 with a 32" inseam. Due to arthritis in my right hip, I shortened my crank length because of pain in my hip on the up stoke while pedaling. After doing so, I saw an increase in speed, due to the lack of pain!!...so, yes crank length does matter! Bottom line, everyone is different, so find what works for you! Smooth is fast!!!

From 172.5 down to 165 on my TT bike and i'm 6f1inch (185.4cm). Theres's a huge diference on my position on the TT bike and my cadence is up... I like it!! On my computrainer I still put the same power (ftp) but I'm more aero and stay easy at 95-97 rpm for a long period... really better for me. I hope this will help some who are hesitant at least for TT bike. (excuse my english, I'm french speaking)

Thanks for a great explanation I have several road bikes with same gearing 53/39 and 13-29 and different crank lengths 170 &172.5 mm Same frame geometry & stem length I really notice the pick- up and speed with the longer crank which suits my riding style - not a spinner but long distance recreational cyclist these days :) 68 yo riding steel

Cycling Bio-mechanics equals muscular considerations (bio) and non muscular(mechanical) considerations. You need to consider what is lost not just what is gained. A longer crank length gives a mechanical advantage of strength (force). A shorter crank length gives a mechanical advantage of cadence (velocity). Power is Force (strength) x Velocity (cadence). As crank length goes up - force goes up and velocity goes down (say 2FxV.) As crank length goes down - force goes down and velocity goes up (say Fx2V). 2 F x V = F x 2V . In practice the power is the same. The dominant factor here is the muscular considerations: muscle length, tendon length, ligament length, the length of the limbs and feet, the speed of contraction and where the maximum power is in the contraction. There is no difference in efficiency because muscle shortening velocities are the same. British cycling have experimented with this and found that there is only a difference at the extremes 1120mm and 220mm. length cranks. The main purpose for different crank lengths is to change the bike fit position - hip closure and hip angle without changing other fit coordinate. Riding a smaller crank will open the hip angle allowing a more prone (aerodynamic) position. In track cycling a crank length of 165mm is used for safety reasons and nothing else. No-one can spin a 165mm crank faster than say a 170mm length. Not even Chris Hoy. Cyclists get good at what they use. Train with 170mm you will get good at this length and so on. E Merckx used a 175mm crank length for time trials and 180mm crank length for hill climbs in the Tour of France.So longer crank length use is not new in pro cycling. I read M Cavendish is using a 182mm down from 187mm. Another cycling myth on the internet.

It also depends on the type of use or discipline of biking you do. Most MTBers go for longer cranks and the reasons are obvious. You need more torque and the longer arm helps in that. Plus in many instances, you don't really need to spin as fast. RB's may be more demanding and if I were a serious or advanced rider, this should already be included in the bike fitting. That may not be 100% or even 90% in some instances. Only long rides and actual intended use will one eventually find out what is good for them. Riding only for 1-2 hours and not for the intended use, may not reveal the problems or issues that can crop up. It's not like any different with saddles. You really have to ride 3-6 hours and do that several times to find weed out issues with your saddle. And one must take it to the conditions one intends to use it or the terrain one is often exposed to. It's really a long repetitive use that brings out the kinks if there are any. And a single ride may not to be smart to conclude anything, especially if one is still adapting to a new crank arm length. Smaller wheels like in folding bikes, means it will be harder to consider longer crank arms simply because those arms can be limiting due to the lower bike stance. Though I have used 172.5mm ones, in 20" tires, it can be tricky not to prevent them from hitting the ground in speed bumps, or some road anomalies. Most folding bikes also tend to be more upright, so those hip and knee angles tend to be not an issue. RB's are usually make the riders lean forward in aggressive aero position which makes those angles smaller. But this is not true for folding bikes, or even other recreational bikes. Hence the issues raised here my not be applicable for some types of bikes. Recreational riders, may not concern themselves with this. If you just ride maybe less than 50km or even 100km, leisurely you can opt out of finding out what's good for you, unless you have long or overly short legs, or some other problem (arthritis, one leg shorter, et ) and the like. Most bikes normally come in 170mm and likely 90-95% of the population will have no problems with those. Of course, the bottom line is for you to experiment for yourself. Everybody is different as well. My guess is if you are a pro, or serious racer, or advanced enthusiast logging in hundreds of km a week, finding out the right crank length can maximize or optimize your potential. It can even help avoid getting injuries.

Nice work on a tough subject, I'm an older rider and I discovered a few years ago that I have less knee pain with shorter cranks, even when bike fit is adjusted.

Crank length is important. As a keen cross country unicyclist, I find choice of crank length is vital. Shorter means I can spin faster but with less leverage; longer gives me more leverage for hills, but a slower cadence. A unicycle is direct drive (fixed gear) so crank length and wheel diameter are the main two variables, and crank length is the easier one to change. However, with very short cranks, you use a smaller part of your range of muscle contraction, and with very long cranks, you move the mass of your legs further. On a bicycle, you are able to choose the gear ratio between the chain ring and the rear wheel. Therefore, it makes sense to choose the crank length solely for what gives you the best, most comfortable and most efficient pedalling action. About 170 mm for a typical adult male, a bit shorter for someone who is shorter, and possibly a bit longer for someone who is very tall. Think of the legs/cranks as the engine. Optimise the engine, then use the gears to direct that power to the rear wheel.

This is a great idea and you should really do this video again, it is certainly worth while! You acknowledge the confusion between Cadence and Pedal speed in the notes you added, but it is not clear when you are using the right terminology and when you are not (thus I suggest a redo!) At the same time, the analysis needs to go both directions. A longer crank gives you more ability to climb steeper hills (by creating a lower gear so to speak); a shorter crank allows higher maximum velocity for a given foot speed( though it requires more force on the pedals) In addition, air resistance is always highly relevant. It would seem that shorter cranks should reduce wind resistance (less overall average frontage because the foot does not go as far from the hip) In addition, there is likely an optimum length for muscle efficiency, as other comments have suggested.

The main benefit of a longer crank (longer end of "normal" range) is when "jumping" in to an acceleration. IOW, when operating at peak torque. This is rare for most athletes. And it's a compromise because you might be losing top end (high cadence) power development. Study power and torque curves of internal combustion engines to understand the torque/power dynamics and then remember that with your own "engine" you risk over-stressing your muscles - an additional risk. OTOH, if you're really fine tuning your form for sub-maximal performance over long periods getting the length optimized can theoretically help with endurance/economy. The bottom line is to err on the side of the shorter crank unless you have lots of testing to validate your reasoning for extending the length.

Thanks, easy to understand. Thanks Angus below as well. I've got a similar problem at age 72. Might try the shorter cranks and keep on pedaling.

You explain things very well. Thanks.

I have used cranks between 165 mm and 175 mm. I found that in effect the main advantage of a longer crank was in hill-climbing. In the end I settled on 172.5 mm as a less tall than average cyclist at 1.68 m. I find with the longer the crank that, within reason, similar results can be achieved in terms of speed [progress with similar effort] with a slightly lower cadence, or as you might observe, a gear one higher than you might manage with a shorter crank. A disadvantage of longer cranks is that you can more easily hit the road with a pedal when cornering at a road junction ... for example. You live and learn on that! But short cranks seem to stress the knees more over a long ride, or even, when weary, starting off. Off course it is all down to personal taste. But if you ride a bike every day, then experimenting is fully worth the effort. Give it a week and decide what option is more “comfortable.” My lowest gear is 44 over 24, which is not really a low gear at all!

Started riding 12 years ago with 175's. I am 5'9".s 31.5 inseam. Use 170's now and could no the happier. 53 x 39

i tested 172 and 175 and difference is noticable, shorter gives more ability to accelerate, it easly rotate on higher rpm. with longer i felt centrifugal force on legs and it accelerate slower, and is not good for high rpm but is better for lower rpm on uphill and if tilt too much in corner longer will touch ground earlier when rotates

Best explanation yet on crank length. 5 stars! Seems awash in the middle ranges of crank length as the multitude of gear choices dominates most rides anyway. Thanks!

This is one of the best videos on crank length out there.!

Here goes something no body has heard, train on bike with smaller cranks to improve speed, then when you race go with the longer cranks to generate peak power

Very educational, I use 172.5 for this reason. I find, for me, it’s the best combination of leverage, cadence and torque effectiveness. I have long legs compared to a short torso, and tend to power my gears, but love to spin to unload my muscles as well as when climbing then apply more power cresting the hill.

Super happy with my upgrade to 180mm

Very good explanation. I am about to order a Falkenjagd Hoplit titanium bike, and given the expense, it really cleared some issues. Thanks a lot! Congrats!

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6 foot 1. Swapped from 175 to 165 on my aero road bike. Have noticed a lot less knee pain and things just seem to feel better. Have not noticed any power differences on rolling terrain.

The shorter you are, the more sensitivity you have to crank length. I swapped 170 for 165 mm cranks on my track bike and found improvement in comfort and position. I am now accelerate seated faster while seated (essential for track racing) so it's totally worth it if you're 173 cm or shorter in height

11:30 If you're spinning out a 53x11 Sir Brailsford would like to talk to you.

My bike fit guy reduced my 172.5 to 170 as I am too crowded (top of pedal stroke) when in the drops. Thigh hits chest etc. My case is I have long legs and short torso, so although my long legs can push the larger crank (175mm on MTB) my upper body is short so the upper body angle is compressed due to a higher seat relative to drops. Its all a compromise. Best fit for road bikes are DUCKS. short legs/long body means you can get 'low as' and not have a ridiculous seat to bar drop. I'd prefer longer cranks as I am less of a 'spinner' but the bike fit says otherwise. SO I had to learn to spin.

The cadence or rpm stays the same but the foot has to travel faster along a larger arc with a longer crank hence foot speed has to increase to maintain a given cadence with longer crank and and slower foot speed with a shorter crank. Foot speed and cadence are 2 different metrics!

A mishmash of facts and info, some of the comments are on point. Changing crank length effects gearing choice. Shorter cranks allow a more aero position and can open up the hip angle which is generally a good thing. I used 170 for years tried 172.5 and 175. Hated them. Am 6' 1''. Am going to 165. Had 167.5 on my track bike I used a few times on undulating super hard training rides. Put something like a 92 inch gear on the bike. Uphills were a grind, steep fast downhills had to break a bit. It is a single speed fix gear track bike! Very efficient feeling on the flats. Get to the front to take a pull spin like hell and just seemed so fast. This is in non aero days, did affix both front and rear rim brakes for group street riding.

im a mountainbiker and im 1.87m tall, but i prefer 170 cranks instead of 175 because my knees feel better with the shorter cranks on longer rides

Excellent video. Explains my recent power average drop since going from 172.5 to 165mm crank. Reason I went down was comfort / bike fit. I'm 5'8 but have long legs and shorter torso. I had a hard time on the flats on a complete aero tuck. My knees would hit my chest so I couldn't get my body low enough. Sadly I seem to have a hard time averaging big cadance numbers (shoots my heart rate to sky) hence the little power drop on my rides. Hopefully I can make it up with getting a little stronger or just practice spinning fast more / improve endurance.

I like to think about the problem in terms of force and radii only, since then you don't have to deal with power and cadences. I approach it as follows: Let f_p = tangential force applied by your foot at the pedal. Let r_p = the radius of the crank arm (i.e. crank length). Let r_gp = the radius of the pedal gear (i.e. the chain-ring). Let f_c = the tension force on the chain. Let r_gw = the radius of the wheel gear (i.e. the rear wheel cog). Let r_w = the radius of the rear wheel. Let f_w = the tangential force the tire applies to the road, at the contact patch. ANALYSIS: Pushing on the pedals produces a torque (T_p = f_p * r_p) on the bottom bracket axle. This pulls on the chain with some force (f_c = T_p / r_gp). The chain, in turn, pulls on the rear wheel cog gear with the same force, producing a torque (T_w = f_c * r_gw). This torque causes the tire to produce a backwards frictional force (f_w = T_w / r_w) on the road, and the road then produces and equal and opposite forward force on the bicycle. The whole equation then becomes: f_w = T_w / r_w = f_c * r_gw / r_w = (T_p * r_gw) / (r_gp * r_w) = (f_p * r_p * r_gw) / (r_gp * r_w) = f_p * (r_p / r_w) * (r_gw / r_gp) Where I've deliberately grouped the radii together in the last line in a rather suggestive way. Let's look at a simple example, where the front and the rear gears have the same radius. My Trek 520's middle chain-ring and its biggest freewheel cog both have 36 teeth, so this isn't just academic. Then the equation becomes: f_w = f_p * (r_p / r_w) If I have 700c wheels with a radius of 350 mm, and my crank-arms are 175mm, then the relationship between the forces is: f_w = f_p * (175 / 350) = f_p / 2 So the force pushing my bike forward is exactly half the force I'm pushing on the pedals with, at any given instant. That's when the gears are both the same size. This implies that a longer crank-arm (or a smaller rear wheel!) will give a bigger wheel push for a given pedal force. Of course, changing the crank length affects body mechanics, and shrinking the wheel radius reduces how far you roll per revolution, so those are the tradeoffs. Next, let's change gears. When the gears were the same size, their ratio was 1. But the bigger the (back to front) ratio, the bigger the push will be, so we want to maximize this ratio. This means we'll get the biggest push on the smallest chain-ring (r_gp) and the biggest rear cog (r_gw). My smallest chain-ring has 26 teeth, and my biggest cog is 36 teeth, so the ratio is: 36 / 26 =~ 1.38 and therefore my maximum push on the Trek is: f_w = f_p * 1.38 / 2 = f_p * .69 So the highest force transfer I can get is about 69% of my input. Now, let's turn it around and see what it looks like at the other end of the gears. My weakest gear ratio (back to front) is: 11/48 = ~ .23 so: f_w = f_p * .23 / 2 = f_p * .11 When I'm grinding, the bike is only getting pushed at 11% of my input force! To get the same push as my strongest gearing, I have to crank about 6 times as hard: 69% / 11% =~ 6.3 The conclusion to all this is that smaller front to rear gear ratios push the bike harder, but you have to spin faster to keep up with the wheels. That's the trade-off for gearing. Incidentally, that's probably where that clickbait ad about the maximum cycling speed being 60kph comes from: 100 rpm * (48 / 11) * .7m * 3.14 = 959 m/min = 57.5km/hr Guy probably just looked at a typical road bike and plugged in what he thought was a super fast cadence. :P

As a short rider i have come to the conclusion bike manufacturers don't want me . You make lot's of good points about 170mm v 160mm , but have you tried to find 160mm cranks on a bike ? Even small , extra small or even extra extra small bikes from the cheapest to the very expensive all come with 170mm cranks , if you are very lucky you might find 165mm , but anything less is custom or very rare. All bike manufacturers are very quick to tell us about their new shiny technology but fail to give us even the option of 160mm or 155mm on small or extra small bikes , this is my main gripe. Many short riders have bikes languishing in sheds after riders give up trying to push 170mm or worse 175mm cranks on their extra small bike .end of rant . Thanks i enjoyed your video .

I just thought crank length was correlated for inseam length, short legs get a short crank set.. I'm 30 in inseam so I switched to 165mm from the standard 170mm, and it feels great now.

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Your video is very in depth and scientific in its analysis. With the growing advent of one by cranks on gravel racing bikes it makes things dificult to choose crank length, size of front sprocket and cassette range. Many riders buying or building a gravel bike are coming from traditional r oh ad bikes. Can you do a video on how you would best take a riders road gearing ( 2x10, 2x11) they are used to and how to best choose crank length, drive gear and cassette range for a gravel bike? Riding off road you obviously want lower gearing than you do on the road but I see riders all the time choose too small of a drive gear and too wide a range of cassette for gravel. There has to be a way of equating a riders road gearing and power output to a gravel equivalent to at least be closer than a guess.

Also rembember shorter cranks can produce less max torque but more even torque throughout pedal stroke. And also it's easier to lift on the upstroke on shorter cranks. Another thing you didn't mention is that if you have poor flexibility its harder to get power through the stroke on longer cranks because the muscles can't fire properly.

There is a benefit to shorter in mtb' ing In that a shorter crank gives better ground clearance when pedalling through rocky sections and later pedalling into a corner and earlier pedalling out of a corner - this would also affect fixed wheel bikes when cornering on road as you - whether this advantage would outweigh the leverage ratio difference would be down to your body dimensions and riding style - there is one other difference more relative singlespeed and fixed wheel riders in that with shorter cranks there is less vertical movement of the legs which would affect rear stability when spinning out a gear - marginal of course but still a difference nonetheless relatable to the engine stability difference of a rotary engine vs a conventional V shaped piston layout.

Great video on a difficult subject. It makes sense to me now why my track coach set my crank length shorter than my road bike 160 v 170, as a juvenile we were restricted with the gearing 45/14. We were coached to spin fast and smooth, something I was unable to replicate with a longer crank. Crank length and gearing in track cycling is very important. This video sorta proves track cycling tried and tested the science way before it was challenged by the biomechanics and engineers. I tried longer crank lengths later but I just found them uncomfortable. It just comes down to what you feel is good and I guess what your body prefers or is used to.

My current bike is 172.5 and I have 29 in inseam. I think I will benefit from 167.5 cranks in my next bike mainly because my knees won't be forced up into my gut like they were with the 172.5 and I will be able to ride more comfortably with a lower bar position.

All this are fairly important to me. I have to race my neighbour to the market and see who get the freshest fish every day.

With shorter cranks you mostly pedal fast, and long - slow, i could ride a 165 but do 170's for all-round use, hills etc... spinners are winners, literally tho at some point you have to push slow gears on a bike, if you go up a rise/false-flat hill...so you have to get back the momentum if in a competitive group sitiuation. Cycles are sold with waaay too long cranks and SHOULD BE selectable, i even dismissed a buy of a bike in a shop once as they didnt have my length of crank and they looked at me like i was crazy!

I have SHIMANO, Claris, 50t, 34t, 8 Speed 12-30 Cassette. 170 CRANK. So far so good, never had any problems.

this was the best discussion on the issue of crank length that I have encountered, mostly because it is universally ignored. I wish the subject of leg length had been brought into the discussion. I am 6'3" and usually ride 175s, but I am a grinder, not a spinner, perhaps longer cranks would suit my riding style. being over 50, my cadence ain't exactly speeding up.

You do realize that there are those of us who do not race but happen to like speed and less knee problems? I ride with 153 mm crank arms and they are fabulous for my 6'1" body. Higher rpm, less flex of the knee, and all the power I require.

I wish I could like this video a dozen times, this was so well explained

There are two more considerations for me. I ride both a road bike and a mountain bike. Mountain bikes typically historically come with a 175 mm crank. I want my road bike to be the same so I'm in no discomfort going from one to the other. The other thing is where does my knee align when my cranks are parallel to the ground. This takes into account both upper and lower leg lengths and should require that a longer leg use a longer crank. In my case I'm 33 inch inseam (838 mm) that also guides me to the 175 mm crank based on using a plumb bob and fit kit.

I find the part at 4-5 min confusing. Seems cadence and foot travel distance is being mixed up. If torque and power is the same then cadence is also fixed. Only crank length and force could vary while maintain equal torque. A nice thing to analyze futher would be the ideal crank length to a certain inseam length. At which radius do we keep our leg muscles working in their optimum most efficient range? Seems to me the more we bend our legs the less power we have. But how short crank is too short then? Also what about the issue of hard accelration (sprinting) requiring maximum leverage (torque) compared to just maintaining even power output (tt?) requiring constant force (power). Maybe less energy is wasted with short cranks if the power is kept constant.

I have gone to 170mm cranks on my TT, Road and Track bike. However have just gone to 172.5 on my TT bike and I use a 60T chainring. The shorter crank length gives me more aero abilities via open hip angle.... I set my fastest flying 200 of 10.9 on a 172.5 track crank.... on a 127” gear (57/12) I find no real issues with 170 or 172.5 in regards to getting on top of a big gear. I have found that I really like 170mm even though I am 6”0.

I'm 5'7" and wear a 30" inseam pant....I use 170mm cranks. I tried 172.5mm with my last bike, and spinning at higher cadences was much more of a chore - plus my hip angle was more acute as my seat was slightly lower (and overall more uncomfortable as well). I haven't noticed any real differences in overall power output however between the 170's and 172'5's with my power meter...however, it was marginally easier to climb steeper grades with the 172.5's.

WELL l did find going from 170 to 175 very odd at first but after proper adjustment of my seat to fit better ,l really liked it along with changing out chainring from 53/39T to a straight 46T with a 12-32 8spd rear cassette on my old steel road bike making a 1x system to simplify my drive train .AS my commuter bike this works great and simplified riding around my relatively flat city ,along with 32c tires to smooth out the bumps :)

there is an error at final on both situations the benefit is from long cranks you can apply more power with longer cranks the cost is on long time efforts when you use longer cranks the push effort is less but since the travel is more the cost you pay is an earlier fatigue.

Short answer - longer giver better torque, but.. foot speed increases & therefore O2 consumption increases .

I absolutley love your no BS approach. One thing I'm missing here is the biomechanical part. What part does leg length play? And especially what part does the length of the upper leg play?

I'm 75 inches tall. I switched to a 180 mm crank from a 175 mm crank, and my regular cadence dropped from 92 to 89. I think it is more comfortable for me, and I feel my leg muscles are working more powerfully. I have always felt inefficient in higher cadences, such as 100, and lower cadences feel more satisfying.

Love the video (and others that you do) and you are very close...at time=4:30 you refer to cadence where more accurately you should be referring to foot speed: To output the same power with more torque (because of longer cranks) the cadence is lower. You do discuss the larger pedaling circle but do not mention that obvious fact that at the same cadence with longer cranks the foot has to travel faster. Might also be worth discussing that many people are considering shorter cranks to allow lower torso due to lower leg lift, and this may improve aerodynamics...

Yeah Crank length matter because with lower and lower BB we hit roots much faster with those long 175mm cranks. 160 FTW

I find longer cranks are less tiring,managed to do stelvio-gavia-mortirolo in one day in attrocious conditions. Just couldnt get power out with shorter cranks.used 175mm vs 165 ultegra which are hollow btw and flex. Im a big heavy guy but power is much better with 175. I rarely get out of saddle on climbs and keep it smooth to save energy particularly past 2300 meters .

Good explanation

You kept relating longer cranks to faster cadence, I think by accident. Tq = F x D. When D is larger, Tq is larger, if Force is the same. P = Tq x Cadence. If P is same and Tq is larger, then C is smaller; so when Distance is increased, Cadence is decreased to yield same Power output. C = P/(F x D).

Great video, the issue I have after a knee replacement I'm unable mechanically to bend more than approx 75° so I have to have a crank shortener on one side so that I can ride, without it I'm not able to cycle.

from 4:32 till 4:53 not true; in that context the cadence remains the same. at 9:40 "bigger crank will enable to generate more force". nope, it's about more torque. my point is this: if you start the name of this video with the word "science" then... just do it for good. in science there are no such mistakes/confusions. regards, Mircea

I read somewhere that as a rough general rule, a longer crank lets you better sustain ave power over time but a shorter crank allows you to produce a higher peak power. Not sure how accurate that is. It might explain why they opt for shorter cranks on the track and for bmx. I've also heard the same thing said about small wheels which would also make sense for bmx. That smaller wheels accelerate quicker for a given power output but aren't as efficient for maintaining high speeds.

Excellent video! Love this explanation

I've done many back to back tests on my mountain bike with 175, 180, 195, and 210 mm cranks. The 210 mm cranks result in 5% faster hill climbs compared with the 175 mm cranks (210/175=1.20 more torque). I'm 6'0" with a 32" inseam. I've worried that the extra leg angle and movement might result in some wear or injury. After 30 years of hard riding with 210 mm cranks I'm still going strong.

This is all new to me I just looked at my cranks to see that they are 175. No wonder I’m a grinder.

Thank you for your videos

Thank you very informative.

Yo utilizo manivelas muy cortas, 125 a 130mm y puedo decir que el pedaleo se convierte con ellas en auténtico placer, la cadencia puede subir hasta las 140 ppm (pedaladas por minuto), implica un ángulo de flexión de rodilla menos agudo, lo que resulta ser fisiológicamente más natural para el esfuerzo de su articulación, músculos y tendones. Tengo que decir que uso una bicicleta reclinada pero creo que el acortamiento también sería conveniente en las verticales, es cuestión de probar, como hemos hecho los usuarios de bicicletas reclinadas

Hard to believe but the most popular cranks only vary in length by 10mm. While a stiffer crank waste less energy, it can cost you money later in life, depending on how fast you are at crank removal. A limber crank rarely gets you in trouble, but your ride will be very unsatisfying.

You can gear up and reduce the cadence as you increase the torque, which requires less oxygen and making more efficient, moreover there is a balance

no no no, cadence is hot the speed your legs are moving but the number of revolutions. longer crank, same cadence, your feet are traveling faster, but you need to sit lower and your knees come higher, restriction the aero position. Therefore, it is beneficial for TT and tri to have a smaller crank. But easier to have longer cranks for hill climbs and more upright positions

Ergonomics of crank to leg length is key for maximum efficiency.

P = F x L x C; if P and F are held constant and L increases, then C must decrease. In other words, at constant power and force on the pedals, longer cranks result in a reduced cadence.

You broke this subject down “Barney style”, a.k.a. clear&concise. Your analysis is on point! Thank you for your contributions!🙏🏾

well i tried 175mm ones then 170mm and then 165 mm ones and i am not sure of anything .....my weight is 170 cm and 81 cm from foot to crotch ....but for sure i know with 165 mm i feel my knees in short of time maybe directly after 4h ride /depends on intesnsity/ .....but yeah my natural cadence is quite low 75-85 rpm

I just found your channel and really enjoy this series; excellent work! Could you please consider creating a video about types of chain rings including osymetric and q-rings?

I love your channel... I love the intelligence/science behind it. But I'm not sure if I would agree with your statement about how a smaller crank length would help you go faster. I can sort of understand where you're coming from about going faster with a shorter crank (you could get more rpm's)... but in the real world, when I think about going as fast as possible, or better yet, faster than my bike can go; I think about the times when I'm going downhill and the speed from gravity has maxed out what my peddling can accomplish. In essence, if I'm at the highest gear but when I peddle it feels like I'm peddling without a chain... no apparent force is being added/applied... in effect, the higher rpm that's needed can not be achieved; I physically can't move my legs any faster. So based on that, wouldn't a shorter crank actually make it worse? A shorter crank would require a faster cadence to equalize what was being done before. So in order for me to go faster I would have to peddle faster, but I have already concluded that I physically can't peddle any faster. So wouldn't it actually be more beneficial to increase crank length in this situation? ... lengthening the time for one revolution so in effect shortening my cadence and therefore giving me the room to add more energy to my peddling... getting more from my maximum peddling speed? I believe the fact is more that it is always better to go with the longest crank length as possible as long as your body's dimensions allow and the terrain/riding-style allows; I don't believe there is any benefit to going shorter in crank length. I believe crank length should be viewed as measured in maximum only... as opposed to a minimum to maximum range. If I am seriously flawed in my thinking, please try to explain... I haven't been classically trained/taught in the sciences.

Would it be reasonable to say that the leg movement/motion is not too dissimilar to walking up stairs. I compared the recommended Australian Stair height from the CSIRO Australia with that of crank lengths and it falls in the same range. It states that the step height is to be not less than 150 and not higher than 180. For health reasons alone - crank length should be considered.

obviously now one has watched the video until its end as they admit within ranges between 120 and 220mm, the crank length does NOT have significant (within 1 or 2%, which is within measuring errors) effect on power output.

Oh... that was a true epiphany. I am on my way to a long adventure and all of a sudden I realize why I have always hated cykling, what it is that is wrong. Only time I really felt comfortable was when I had a huge 28" Kenhill. I sold it because it was to big for me but it probably had the right crank length for me because ever since I have had that feeling of driving this little kids bike.

Thanks for a nice explanation.

Why would it be harder or slower to accelerate a bicycle crankshaft of longer length when it is easier to turn a longer lever? Shorter cranks will not increase your speed going down hill. If anything you may go slower and as you will produce less power at the crankshaft to push through the wall of air. The longer crank is easier to turn thus you can turn it at the same speed or faster. The larger circle created by the increase in length or the time it takes to turn the crankshaft one rotation does not decrease the pedalling efficiency. The front sprocket (constant lever) size is what matters in that regard. The crank arm and from sprocket rotate at the same RPM even though one travels further than the other. The larger circle means the duration the force is applied to the front sprocket is longer thus a smoother or less pulses on the rear wheel as you would hear on a indoor trainer. The loner crank also means you can more use of your muscle especially your hamstring muscles. When you do leg curls do you limit how far you contract your hamstrings to left the weight, I am sure you lift weight at lest 90 degree. I use cranks with a length of 210mm and it is much smoother, cadence is still high (105-115), ride a smaller frame, pedal does not hit the ground. The only thing that really took getting used to going from 180mm to 210mm cranks was when you stand on the pedals. climbing Leaning forward felt weird (like being on a step climber in the gym) not inefficient, just different. But if you position yourself over the seat....holy crap the bike shoots forward!!!!! IT felts smooth and you feel the force you apply to the pedal going out the rear wheel!!

... to put it simply. the bigger the chainring/cog ratio, the bigger crank length required for pushing power, based on leg inseam length.

If we consider the crank to be a wheel and axle machine, changing the lever length wouldn't make us any faster or slower than adding a smaller or larger cog to the cassette, right? Our bodies are the source of horsepower, not our gearing. But as you said, comfort is what matters. It's called a crank (and not a lever) because it converts the linear movement of the connecting rod (our leg pushing down) into rotation. Biomechanics is the only question.

im around 5'10.5", with 32" inseam and i went from something around 165 to 175mm, and luckily i really nailed it. if i used the currently favored formulas (height x .095 or (inseam x 1.25) + 65) i should supposedly do 170mm.. maybe its because im a pedal masher but 175 really feels optimal to me

It's the same as with diesel vs gas. Diesel produces more torque due to higher compression ratios enabling diesel engines to have longer cranks, but they don't produce high power because they can't rotate these cranks fast enough. So they produce more power than gas at lower rpm. Gas engines have shorted cranks they can spin quickly producing more power at higher rpm. What I'm trying to say is that shorter cranks will help you produce more power if you can maintain higher rpm. Also, when sprinting, it's better to go at very high rpms instead of crunching the gears slowly. For example bmx racers will hit 200 rpm with 2000+ watts when sprinting out of the gate. So do track sprinters. But for humans there's also the stress you put on your muscles and joints when pushing low rpms with high torque. My conclusion is shorter cranks are better either way, because they allow you spin faster, even if you think of yourself as a diesel.

So, you should first decide on the crank length based on your personal pedalling "comfort". Given the selected crank size choose then the sprockets/ chain rings to not run out of gears.... The confusion is because people tend to think in reverse order.

Buy a variable length crank, and see what your power meter tells you. I think that the body is adaptable to some extent, and all variations provide opportunities for strength gains. Three versions I've come across are: 120 to 160mm, 150 to 190mm, and 180 to 220mm variable cranks. I'd love to see a variable length crank designed for permanent use that is extremely light, and you could alter it on the fly with some type of stable nano motor. (I'm dreaming now) Note that the seat post should be adjusted as crank lengths adjust. These variable length cranks can be heavy. Maybe permanently install on a training bike for strength gains. careful about cornering when at the long ends. A high positioned bottom bracket provides the greatest clearance. I think we should be able to rent them for a period of time, learn what you can while renting them, then return them so someone else can do the same. www.hscycle.com/Pages/adjustablecrankset.html

im guessing this is why pantani was running 180s in the mountains. easier to turn around the 39/25 on the steeper grades. i live in an area where you run out of gears even with a 34/32, so the longer cranks do help on the over 12% grades i find. not sure why gravel bikes come with 1x, just not enough gears, not easy enough and get spun out to easy also

I got a bit shorter 170mm cranks to avoid touching the street with the Pedal in corner

Also to add with longer cranks you might find yourself hitting in the chest with your knees.

The crank arm length certainly is important and this subject is misunderstood. But this video is riddled with errors. The author is to be credited with recognizing the value of proper crank length but he is in way over his head regarding the details. The crank arm length has zero effect on the calculation of the gear ratio. He's calculating something else -- not the gear ratio. The biomechanics of the leg and foot during the pedal circle is explained incorrectly and the significance of pedaling efficiency to crank length is not explained correctly. It is not a simple mater of leverage -- it also changes the length of the arc where force is applied efficiently and comfortably. Cadence is repeatedly misused in the explanations. Cadence is simply rotations per minute -- nothing more. Because of the many errors in this video, it undermines the very real need to understand this subject. Finally, the rider's body geometry is ignored yet the optimal crank length is strongly affected by it as well. For example, in a forward-leaning aero tuck (think a TT bike), the body mechanics require a shorter crank arm compared to a more relaxed geometry.

So there is no real change in average power or efficiency, but long cranks are more likely to get you out of trouble (stalling on a steep climb, somebody jumps in the last km...). So if you train your way through the niggles and set up your bike properly, go for long cranks. Spinning out on 53/11, on British roads, ????

I'm 5'6" and presently using a 177.5mm crank on my road bike and i like it. Based on my height i should be using a shorter crank like 172.5mm. My previous crankset was actually 52- 39 with cranklenght of 172.5mm and the right frame of 52cm . My bike weighed 9 kg at that time ( i'm 52 yrs old andmy weight is 83 kg). Every saturday we have a 20km race (mostly flat) which i enjoy participating even if i always find myself struggling and finish the race dead last. The ride is really fast abt 47kph average and i begun to admit that it's the age factor which dictates my performance, until i watch some You tube videos which discuss this interesting topic about crank lenght., compact crank, proper cadence etc. The next morning i look at my bike and did some experiment. I went to a bike shop and have my crankset changed to compact 50-34 and crank lenght to 177.5mm furthermore i changed my wheelset with aero type but much heavier which made my bike 11 kg total weight . Afterwards i did some rides alone and one thing i noticed about the long crank is i can really feel the roundness of my pedal strokes. I'm not sure if it's the cranklenght because 3 weeks after and until now i've never experienced getting dropped in bunch rides with speed ranging from 45-53 kph in this 20km flat ride. One thing i noticed with long crank is it helps in getting high speed and momentum. Maybe it varies in each individual but could be the reason why Greg Lemond used this long crank in his epic Time trial and victory the Tour de France in 1989.

Great info. Thank you.

Lots of great information...I also wonder what effect a 5 pound ballast weight at the end of a crank arm would accomplish...Wouldn't that turn your crankset into a pendulum...Making it easier to maintain momentum...Which theoretically should translate into climbing hills easier...Just curious...

Leonard Zinn SWEARS that taller riders need longer cranks. I am 6'3" with normal length legs for my build and I use a 175 on my road (race) bike and 180 on my TT bike and can't really tell a performance difference. I want the clearance during criteriums so I don't see any reason to go past 180 as I've scraped a pedal a few times just with 175s. And thats scary at 30 mph in the middle of a corner!

NOW on my carbon race bike l have a 172.5mm crank mated now to a 50/39T chainring and 12-28T cassette .Being fighter bike l can use a higher gear ratio than the bike below overall but l spin them faster and l get pretty much the same top speed between the two at around 46km/hr which is more than quick enough .AND on windy days around 35-39km/hr ,which is also fine . Funny how both bikes with different set ups end up same results BUT different feel between the two. RACE bike feels zippier and old steel more relaxed :)

thank you for the video, it is helpful. There is just one thing I cant get my head around, the relationship you mention between crank length and cadence is the other way around, isn't it? if 160mm requires leg to travel 1005mm while 177.5mm requires leg to travel 1115mm you need to rotate more times with the 160mm, all else equal, to produce the same effect, thus more RPMs = higher cadence. So the smaller the crankarm, the higher the cadence all else equal.

short crank makes you climb faster?long crank makes you go faster on flat?