Actually, there is quite a bit of literature written about the subject but you're not gonna find it in blogs about cycling, cycling magazines, or the mainstream media. I read 5 peer-reviewed scientific papers about it just today but they were papers I found from my University library website. They were papers from publications such as the European Journal of Applied Physiology (they're quite long, just read the introduction, abstract, and the discussion sections of the papers; the results section won't mean much to you lol). They test crankarm lengths from 130mm to 220mm. What I conclude for them is that going to a shorter crank arm length does not change much your average power output over the long haul, however, with a short crank arm, you can reach your peak power faster. What that means is, if you participate in events like cross-country mountain bike racing in which getting in the best position from the start is very important before you get to stretches where it would be difficult for anyone to pass you, a shorter crank arm would serve you better since you can reach your peak power significantly faster, you can put yourself in a winning position faster. Another research paper found that the optimal crank length for maximum power is 41% of your tibia length or 21% of your leg length. Another paper found that shorter crank arms are more efficient because you consume less oxygen over time. The amount of oxygen consumed is directly correlated to the amount of energy you spend. This is because with shorter crank arm lengths you are able to get into a lower aero position without your knees hitting your chest. As a result, you can reduce the amount of drag by 30% in some cases. Yet another paper found that the shorter the crank arm, the faster your pedaling rate (cadence) using the same gear. That can lead to your going a little faster. Like I said, there are quite a bit of scientific studies conducted regarding the effect of crank arm length on overall performance, but you're not gonna find them just by googling them. You gotta go to those peer reviewed scientific sources.

I've absorbed quite a bit of literature on crank length. Lennard Zinn states if you want to produce more output, go with longer cranks. Here are some considerations if you should go with shorter or longer cranks: 1) your cycling activity dictate how much clearance you need from your bottom bracket (ie: cyclocross) 2) crank length should reflect a ratio of your leg length proportions (ie: Quintana vs Van summeren) 3) your preference of being a spinner vs a masher for cadence 4) the frame size of your bike (related to BB clearance and front wheel turning clearance)

This is awesome! As a bike fit specialist people are always worried about going to shorter cranks when I recommend it, I now have something to show them to ease their apprehension, thanks guy!

The key here is that both your subjects are around 6 ft tall. In my experience, short cyclists are much more cranky.

One consideration of mine for switching Tia short crank length was hip angle. A longer crank will result in a longer leg stretch at the bottom of the pedal stroke and a more acute hip angle at the top of the pedal stroke.

my favorite kind of "science" obtain a single point of referrence, extrapolate graph to infinity.

Longer cranks will give you more leverage and make it easy to turn the cranks by quite a bit but how well that works will depend on the circle size that your leg length makes if to large or small they will take away the point (when pushing down) where you get maximum power for leg length.

I'm 6'8 and ride 180mm cranks, found them to be the most comfortable. Isn't the most important thing when it comes to cranks is if they comfortable to ride in without any extra strain or pressure put on the legs? Gear ratio will do the rest.

There is one very important aspect that you have not considered in this study: what is the ideal crank length that would allow Matt to clip in like a regular cyclist?

I switched to compact cranks and dropped from a 175 to 172.5 arm and found the difference amazing on hills. Maintaining a higher cadence has improved my times with less effort. I am 185cm.

it's great that you have made a video about this, most journalists as well as most bike dealers completely ignore that (to save storage space and to simplify delivery). But the problem with those tests is, that any experienced rider is used to a specific crank length and his/her legs are completely adopted to that. So, even if another crank length would give him/her significant benefits, you will not see that at once. I use 180mm cranks (90cm inseam) and if I go to 172,5 I feel not good and loose power. So I think for my long legs the long cranks are better... but of course there are riders with long legs who can ride faster than me with shorter cranks. On the other hand, riders of custom made cranks as Zinn or Marshall (with extrem range from 130 - 220 mm) are often enthusiastic, so...

I've just gone down from 172.5 to 170mm more on hunch than anything else. I'm glad you've just confirmed I won't be losing anything. Thanks again GCN.

With Shorter cranks a more Compact Body Position and a greater height difference can be used because The knees are lower in The highest Point of The pedalstrole. Furthermore larger riders have Less Problems with Steering while The feet/crank Arms are in horizontal position. Like Compact cranks, Shorter crankarms will be Applied on The Long run.

I did this type of testing for crank length quite awhile back. I'm 6'-4" and have a 38" inseam. So I was keen on learning if longer cranks would work better for my longer legs. I took a slightly different approach. My thought was the important number to know was efficiency at my race pace. So I established a baseline power reading on the standard 175mm cranks for a 10 minute effort at a heartrate of 170bpm. Then I did the same 10 minute effort holding the same power readings, but looked to see what my hear rate was on the longer cranks. The theory being, at the same power output, if my heart rate was lower longer cranks would be more efficient, and if my heart rate was higher longer cranks would be less efficient . The 177.5mm cranks lowered my heart rate by 10bpm. The 180mm cranks only lowered my hear rate by 5bpm. I did notice that the 180 felt quite different, and I wondered if the lower decrease in my heartrate on the 180mm (vs. the 177.5) couldn't be attributed to the different feel and I thought maybe the 180 might be more efficient if I spent some time on them and 'got used to them'. I ended up going with the 177.5 for several years, and was quite happy. Then two years ago I got a new mountain bike that came with 180mm cranks. I looked high and low for a set of 177.5 cranks to swap out, but I could not find any compatible cranks. So I gave the 180mm cranks a go. My previous suspicions turned out to be correct. I got used to the 180mm and noticed a 'noticeable' difference between the 180mm on my mountain bike and the 177.5mm on my road bike. So I swapped out to 180mm on the road bike as well. I highly recommend everyone do a similar test. As 10bpm is a significant reduction in effort. Find a good bike shop that has a fit bike with adjustable crank arm length and a power meter and test the different lengths. I'd highly recommend doing the test 2-3 times. One, it allows you to get used to the different lengths. Two, in my test the 180mm was done last, I think I was just a bit tired from the baseline 175mm and first run at 177.5mm. I would have liked to done the test a second time and started with the 180 on fresh legs.

I'm 6ft3 and went from 170mm to 155mm and then even to 130mm. It takes a bit of getting used to but once there, the shorter cranks are at least as efficient as the longer ones. The reason for me having such short cranks is for one that I fit in a smaller velomobile and secondly I found that my knees feel better after a long brevet with the short cranks. I took up a bigger sprocket on the cassette to counter for less leverage of the short crank on climbs.

I'm 5'8". I recently got a Cannonade CAAD10 with 172.5mm cranks. I swapped them with a set of 165mm cranks off my vintage Bianchi... it was much more comfortable, and I could maintain a higher cadence.

05:09 fake tea drinking :-)

Just recently went to 167.5mm cranks purely on the basis that they were fitted to the secondhand bike I bought. What I have learned in the weeks since is that you will be happy with whatever length is on your bike and you can find justification for one side of the debate or the other to make yourself feel good about the choice you make (or have thrust upon you).

You guys do some really interesting tests but unfortunately they provide little more than entertainment value with such small sample sizes. Not knocking your efforts, would just love to see these GCN Science videos with an N value of more than 1 :)

From years of mucking about (44 to be exact) ...shorter cranks on long rides=less fatigue...apart from that no difference , just use the gears to compensate and adjust cadence....All my bikes have 165mm cranks at 6' ( i have disproportionately have long legs). Worth trying for long rides and climbs....plus when on a fixed less chance of grounding out....Smaller circles I think is the reason for the reduced fatigue, and possible efficiency according to an engineer friend of mine who commented on this subject, he has changed down too.... Worth noting crank length was initially decided by penny farthings single gear to get it rolling, so one would surmise that longer cranks would've been the preference, so no science and thus the conclusion of ironman triathletes who have studied this (ie papers) that 140-150mm for the 112 mile section are the most efficient for aero and efficiency when racing..... As usual the burden of History holds road cycling back as well as our friends at the UCI, love em or loathe them, Triathletes are at the cutting edge...Ask Greg LeMond, (alas you can't ask Mr Fignon RIP).

I think you need to do the tests over separate days due to performance dropping due to fatigue.

Very interesting as always, guys, but I can’t help thinking you’ve missed something important. For years, knowing your ideal crank length was essential when you ordered a frame to be made for you, and the (metric) formula that I always used was / is Inside-leg measurement in centimeters (barefoot) X 1.25 + 65 = crank length For me it is 80 X 1.25 = 100 + 65 = 165 ... my optimal crank length is 165mm (6½ inches) I have experimented over the years - 165mm = ideal 170mm = OK but be careful 175mm = knee problems Any measurable performance is immaterial. Today bicycles are sold as complete "units", the manufacturers determine the crank length, and the forums are full of people complaining about mysterious knee pains that won’t go away.

Why only the 162,5mm, 172,5 and 177,5mm cranks? Wouldn't the 165, 170, 175 and 180 be more logical? (Or at least more logical to include them)

A little basic physics is needed here. Riding at the same speed it should be fairly obvious that the same power is required whether using short or long cranks. With shorter cranks a rider must compensate for the lower leverage by either increasing pedal force, or increasing cadence (as power = torque x cadence and torque = force x lever arm). All other things being equal, when riding at a given speed, switching to shorter cranks will tend to encourage the rider to select an easier gear and spin a little bit higher (putting more load on the cardio vascular system), whilst switching to longer cranks will tend to encourage the rider to drop cadence a little by selecting a harder gear. Ultimately most riders will adapt to whatever crank length they are using, and given the range of difference in crank length is quite small (+/- 3% - 4% from 165mm to 177mm relative to a 'standard' 172.5mm) other factors such as comfort are more important.

I can definitely see advantages to shorter cranks. You might get a slight increase in aerodynamics as shorter cranks will let you run a slightly higher saddle allowing for more drop to the bars while also making riding on the drops more comfortable as your knees won't come as high on the upstroke. Also shorter cranks will have better cornering clearance allowing for more peddling through corners. I also remember Simon commenting in the video of Wiggo's new bike that he was running shorter cranks.

Interesting indeed. Has GCN investigated mid foot cleats?

This is my favourite series. Apart from the ones you arrive at, the viewers, I'm sure are able to form their own conclusions as well. Thanks for the great content, cheers!

Guys, you need to get back to this one. You forgot to adjust the saddle height! When Si went from 172.5mm to 162.5mm cranks, the bottom of his pedal stroke shortened, so to adjust he needs to elevate his saddle by 5mm to readjust both the minimal and maximal knee angle. He could also increase it to 10mm to get the same maximal knee angle but a smaller maximal angle. The saddle also needs to go back by 10mm in order to adjust for the knee angles at the horizontal position.

i think there's a lot more that could be done in this subject. For instance, Simon is obviously used to his 172.5 cranks. it shows in his cadence and the numbers done lie. There muscle memory involved in that as well as the riders perception. It probably would be a better study if they were to use someone whos had shorter cranks for a much longer time. Compare this with someone who's been exclusively using longer cranks for a similar amount of time, and have them both switch. Simon is right smack in the middle in terms of crank lengths, so his numbers would obviously show that he's average compared to both crank lengths. From my experience, i went from 172.5 cranks for a year, to 170 another, then down right to 155! Initially, i found the same findings these GCN scientists found. I was unable to generate much torque power for climbing off the saddle and sprinting with short cranks that i could easily find comfortable in longer cranks, however my cadence stayed consistently at 90 RPM, where my cadence with longer cranks were consistently 70-80 rpm. In my opinion, crank lengths are generally a personal preference. These guys had the same findings i did, however i found more pros than cons with short cranks than longer cranks. Given time, short cranks also help with your pedaling stroke. Simon would not notice this because he is a very experienced rider, but for most of us our pedaling technique sucks! Short cranks help even out your left and right pedal stroke in the long run... it helped a little for me, but then again im only mortal :) You've gotta keep working on pedal technique tho with single pedal drills or the expensive and controversial POWER CRANKS? i digress... bottom line, try different cranklengths and find out for yourselves what works for you. * im not a scientist or a professional or anything in between those.. just a dude, who likes to tinker with bikes every now and then :) peace!

Excellent guys, very interesting to explore this variations!

Awesome vid guys. I'm dead set the same size as Mark Cavendish (wish I could ride like him!) 171cm - 5'6", 70kg and short legs. I started out on 175mm cranks and quickly changed to 170mm ones. I'm also more of a natural sprinter, but it made a huge difference to my comfort, loading of the knees and especially climbing efficiency. So in conclusion... totally agree with your findings!

after 20 years on 177.5 , i dropped back to 175 for my road bike & bought a cyclocross bike that had 172.5 my knee pain of the last 3 years has gone away and have found i am spinning more on lower gears too proving that aging bodies, long cranks & big gears are not a happy combination and that as you progress you need to change to reflect your capabilities.

New winner for 'worst ever fake tea drinking'. Christ Matt - you've even gone for the lick of the lips!

I'd agree that slightly shorter cranks can be better. That said, I have a 970mm inseam and I use either 180mm cranks or 200mm. I know the 180mm for me are faster than 175mm, as proven in races. 200 for me are fine for everyday but long for racing. I reckon optimal for my leg length is between 180 and 190. So perhaps a crank length ratio of between 18.5% to 20.5% of leg inseam could be pretty close to ideal. Keep your crank length slightly shorter if you're using them for racing.

i am 5'7 and use a 180 on my left leg and a 162.5 on my right leg and hang my big old head all the way to the left on a 43 degree angle for a counterlever effect. the hardest part is the constant whiplash from all the head bobbing. once i reach 40km per hour, the aero effect really kicks in !!

Love your videos guys. As a science guy myself I love the perspective you have. One consideration you didn't include in the video is pedaling through a curve. Assuming the bike is the same, if you just swap the crank arm length then you can't lean into a corner as much with a long crank length as you can with a shorter crank length without striking the ground. This is especially important in crits and for guys who use a pedal with a larger body like the early Look clipless design.

My Synapse came with 170 crank length which I have always thought was odd. I no longer question having them. Thanks

That I want GCN retest again!

So many variables to account for with crank length.. One thing worth thinking about is adjusting saddle height and set back to maintain similar knee extension and knee over foot positions between each tested crank length. The main rule of thumb I've always gone with with good results is basing crank length recommendations off of hip flexion mobility. No matter how much mechanical advantage or leverage gained by longer cranks, it will always be eclipsed by the loss of power from having to 'go over the top' of the pedal stroke through mobility restriction or redistricted movement. FYI, at 6'2 I've been loving 170mm cranks for a few seasons now, able to have a lower handle bar position and ride in the drops very comfortably :)

There is a ton of variables to this question. The main variable for me was my shins are longer in proportion to my thigh bone. At 5'10" a 175mm caused my knees to hit my ribs. Going down to a 170mm allowed for a faster smoother cadence

I am a very short 5'2 rider (158 cm). I have rode on 165mm cranks over the last several years. When I puchased my current bike in November it was very difficult to find a 165mm crankset for the force 22 component set I am riding. The 172.5mm set that came with the bike occasionally touched the ground around corners and I have had no such issue and a generally more comfortable ride with the smaller crank arms. They do not make 162.5 for the force 22 and the Red set is out of my budget. If you want to send me a pair of 162.5 Red cranks I would love to test them and report back! ;)

Matt's drink of a cup with no tea was actually quite funny!

From what I understand, there's a movement in triathlon towards shorter cranks to encourage a higher cadence, leaving the legs fresher off the bike.

Simon, did you adjust your saddle height so that your leg extension was the same in all 3 tests? You've opened up a can of worms with this video, I would like to see this issue investigated much more thoroughly. This is one of cycling's biggest controversies. Good job guys.

I really should have started to watch this channel before... i'm a short rider (1,69m) and was lead to change my crank lenght (170mm to 175mm) cause that is what every other rider in my region uses... Anyway, great channel, great tips. Keep up with the great job!!

every damn bike question i have... GCN has a video for it. this world is an amazing place.

Good video guys. This topic was definitely begging to get a "GCN does science" video done. It'll be great if you guys could see how your conclusions fare against some of the pro-riders and their cycles which you have already reviewed.

Good subject for the upcoming pro season vids - height of pro riders versus their crank length and performance record?

I went from 175mm cranks to 170mm cranks. my sprinting power actually was slightly lower than before(even with the right gear), but my max cadence went up to a whopping 150rpm from 138rpm. Especially when time-trialing and at threshold pace, higher cadences are a lot more comfortable for me. 100-110rpm average is normal during those sessions. Plus, i get less of that stomach kicking feeling from my legs compared 175mm cranks when using aero extensions and having that low upper body position. Im 5foot 11" or 182cm tall, so no odd size there with relatively normal sized legs compared to the rest of the body

I had tried 2 different crank length, 160mm and 170mm. What I don't agreed that by shifting of gears you can achieve the same speed. I had tried on a 1km stretch down hill at different gearing the 160mm crank best result is only about 56km and the 170mm crank had a speed of 59km. So torque come into play alots, just like you are powering up a climb , down hill or even a flat, then initial advantage will put you ride at the front.

I use 165mm for two reasons. First reason, after a crash (my knees always take a knock when I come off) I can return to cycling sooner with shorter cranks. Longer cranks mean I have to bend my knee more at the top of the stroke, so 165mm means less discomfort. Second reason because they are shorter there's less chance of grounding when powering through a roundabout or corner.

that was the worst fake drink of coffee matt! (5:05)

Thanks fellas! I was really excited when I heard on the GCN Show that you were finally getting around to posting this video. One suggestion: Test your shortest (Tom?) and your tallest (Surely gonna be The Boss) side by side and see if you can get a more conclusive result. Thanks regardless. (This was my Facebook question that you answered live, in case you'd forgotten.)

Interesting video. My bike came with a compact 50/34 170mm cranks. Was tempted to try a bigger chain ring as I was finding I was riding in 50-11 a lot. Mentioned it to a mate who gave me a 52/39 chainset. Fitted it and only then noticed it had 175 cranks. My legs did have some funny aches for a while after fitting but it subsided. I have found that the longer cranks make me feel stronger on climbs particularly when out of the saddle but I don't reckon I can spin them as fast. Overall pace averages out the same. I'll keep the longer ones as 105 looks much better than the square taper FSA I had before! BOO! ( just in case you had dozed off ) :D

best is simons: "uhm" kind of sound at the very end :D put that in a loop, FANTASTIC!

Si you mention you have a 'preferred cadence' but it was noted on the long crank your cadence was slightly lower. Maybe this could be attributed to having a higher leg speed for a slightly lower rpm, and it's the leg speed you are comfortable with and not actually the rpm? A trick that some employ to effectively lengthen any crank length is to move your cleats back on your shoes to increase your leg speed for a given rpm. I think for very long legged riders with legs of high inertia and mass, a longer crank is advantageous due to the greater time in the window of the power arc (say 2 oclock to 6 oclock). Would be interesting to see the results for say a 185mm crank and Q rings to see the extremes. For blood lactate and possibly HR the readings could have been within the error boundaries.

I use 165 s on my enduro as I get less peddle strikes during suspension sag , I find short bursts between jumps out of the saddle are quicker in fact any out of saddle peddling is great but I do miss the all out tourque and grunt of a longer crank. HOT TIP ! I'm going go fit a cheap lever action dropper post to my gravel bike soon and I think you guys should to !

I think it was a mistake to measure power at the pedals only. Wouldn't it be possible that the longer the lever the less power you need to achieve the same output power at the back wheel?

I like these videos, how about one on how different tyres effect rolling resistance.

Well l have all crank lengths on all 3 of my bikes and I have discovered the differences .first mtb 170mm 1x 34/32 gears fast spinning. Next steel road bike also 1x 46/32 gears stiffest gears low cadence, lots of torque with 175mm cranks !! Finally carbon road bike 50/32 speed/torque but medium cadence with 172.5mm cranks perfectly suited here!!

My wife went from 170mm to 165mm. She used to have a terrible time at about 3-4 hours in the saddle. Either we'd raise her saddle and she'd have awful seat pain. Or we'd lower it and she seemed to have trouble at a tempo speed (which for us is 15-18mph on flat roads). Heck on the longer arms and at a lower saddle height I was able to pass her on a 12% incline hill and I weigh about 2.5 times as much as her (she's petite and I'm over 100 lbs overweight still). The shorter arms seem to have allowed more of a sweet spot for her saddle height where she has enough power without too much pain. Definitely something to consider if you've had a terrible time with finding a good fit on your bike. She is using a woman's bike (Trek Silque) but has relatively short legs for a woman. The 5mm difference seems to have been huge for her in terms of comfort while maintaining some power. Now if only she could get out of the habit of riding at about 75-80 cadence in a higher gear. She seems to get knee fatigue on 50+ mile rides and we're both working on practicing higher cadence riding when we are on the trainer inside. Me so I can get used to climbing low to moderate inclines at a higher cadence (I always tend to switch to 75 soon as the incline slows me down which is about 2%. I'm trying to teach myself to spin up those less steep hills and the hope being my quads don't burn quite as much on hillier rides. But at my current weight I know it will just hurt. More motivation to keep losing!) and her on the flat sections.

Matt's pronunciation of "Ability to Sustain" is about as good as his clipping in.... on a bad day ;) 1:40

Of course crack length matters. You don't need to watch the video to understand that torque = force x radius so if you have a bigger radius, then you can apply more torque... Although I'm sure you don't want to go over a certain length because of muscle composition and other stuff I wouldn't understand

I found the max power results interesting but I had expected that the main reason for using different crank lengths is injury prevention and comfort. I have two cranksets, one that came with the bike - compact (175mm) and one I bought as an upgrade - full size (172.5) and the only difference besides my chain rings is that with the 175s I have to be conscious about when I pedal through corners

The new thing in My local area Mid Atlantic USA is to have shorter cranks and compact gearing, better on Your knees and faster to spin out!

For really short people: cranks can be found as short as 125 mm (these are triples), with both 145 and 155 mm readily available as well. Recumbent specialists will know where to find those. Even for 'normal' sized people a little shorter may be nice, especially if you have sensitive knees. Just make sure you downsize your front blades as well. I'm 176 cm tall, and use 155 mm cranks on my recumbent, and I love it. Yes, your cadence will go up, the (linear) speed of your feet will stay roughly the same. Note that crank-arm calculators will limit themselves to what the major manufacturers are selling (typically 162.5 to 177.5 mm), not necessarily to what you may actually need.

Can't shorter cranks benefit TT riders? When pretzeled down into the TT position, don't most people find it slightly harder to raise your foot over the top part of your pedal stroke? In this case shorter cranks would give more room?

I rode for a while on my commuter bike with crank arms that were too long for me. This caused me knee problems after several months. Switching to shorter crank arms solved my knee problems!

As if we needed anymore proof....Sci's max power was only in the 900 range while Dan's was over 1,000 watts in the previous video, confirming once again he is the boss.

It would be interesting to see how the shorter crank length affected hip angle at top dead centre and therefore whether h'bars could be lowered to improve aerodynamics and reduce frontal area & reduce drag. I think this is something pursuit teams have been looking at but could also be relevant to TT and triathlon

I've always had a thought that shorter cranks could be beneficial for TT/aggressive positions. If your position on the bike remains unchanged with a shorter crank length the hip angle would increase at the top of the pedal stroke, meaning you could either produce more power with the same position or become lower at the front end/more aero for the same hip angle as the longer crank... = going faster for free!

Riders who used 180mm cranks: Marco Pantani, Johan museeuw.

As others have suggested, it would be interesting to see this redone for a time trial position where shorter cranks allow for a more open hip angle.

But... but... How do I find the proper crank arm length?

I'm 6ft and when i had a bike fit was given some 165's to try and help with an old knee injury. Been on them ever since.

They tested for several things but failed to mention the only thing that matters, speed and acceleration. It's not about how hard your body works, it's about how fast the bike goes. Crank length doesn't really vary with height it should vary with leg length. There are formulas to calculate crank length based on leg length. In the past I have used one devised by Greg Lemond but not sure where that is. That gives a ballpark but there can still be variation for femur to tibial proportion and even length of foot. As well if you want to wind the bike up faster in a sprint shorter cranks can be helpful. OTOH more torque for climbing or TT may benefit from longer cranks. Anyone is likely to be biased toward what they are used to riding. Anyone who doesn't think crank length matters should drop or raise their saddle .5cm and see if they notice. The .25 increments on cranks effect top and bottom of the stroke so each one is effectively .5cm in the saddle. Mentioning these factors would have made this much more informative. As is it's largely just tea drinking and yakking.

I read the "Well Built Triathlete" and it says to go shorter for better run results. Watch this, now I may just after all!

GCN Does Science: What is the optimal level of tea consumption for coming to conclusions? and how about How to Make Tea Like a Boss?

Thanks for the video. As a 5'5" rider, needing shorter crank length what are brands the that makes 155mm - 160mm

thank you Simon for your sacrifice, for science.

i used 170 and 175. but i feel more comfortable with 175...im 5'7'' tall. im not in competitive cycling but i ride my bike a lot. i think crank length is a matter of preference.

gcn im a track cyclists and i ride my track bike on the street so since we dont stop pedaling 165 crank arms help us do more sharp turns

I went straight to the conclusion part of the film and it agreed with what I intuitively felt. I'll watch the rest the film,

I'm 186cm tall 88cm inseam. On my roadbike I have 172.5mm crank, on MTB 175 and on CX 170. I'm quite comfy on all of them :)

The larger the crank arm is less effort more work done. It’s basic laws of physics. It’s called Folsom theorem. Then it gets into size of rider and comfort of peddling stride.

A few companies supplying shorter cranks... Middleburn, Lightening, TA, and Rotor

Actually the crank length influences directly the torque on each pedal stroke, changing gears will impact the distance moved per stroke and also the required torque. So, when comparing one pedal stroke in the same gear, same power input, longer crank will indeed produce more torque. That's pure mechanics.

Shorter cranks are definitely advantageous for short riders trying to achieve an aero position, especially during a time trial/triathlon. The shorter cranks let your knees come up less so that they do not inhibit your breathing, therefore you can achieve a lower, more aero position.

My wife has had a total knee replacement & just cannot get her knee to bend enough on the up stroke using the 175cm cranks on our hybrid bike which we use on a turbo trainer. Current cranks are FC-M311 Shimano. 150cm would help enormously but where to buy affordable substitutes? SE Essex.

You should try this test again with different size people. Also in different gears for a complete test.

What are the pros using? Is Nairo on shorter cranks? Is tom Dumoulin on longer cranks?

shorter ones are easier on the knees. mike burrows has done a lot of work on the subject. at the other end of the scale Ryder hesjdal and Adam Hansen both use 180mm

My LBS changed my crank length from 172.5mm to 170mm when updated my drive-train to Ultegra Di2, they recommended it as I am 5 8" , but to be honest I can't really tell the difference at all.

Fit trumps nearly everything, however all things being equal, the longer cranks should give an advantage due to fulcrum length, however the overall motion of the foot travels nearly an extra 100 mm with each cycle. Keeping that in mind, it does explain the lower lactate and the higher watts at sprint speeds. Again going back to fit, none of that matters if the longer cranks force your knees into a disadvantages position. Best example would be that a squat of only 1 foot distance is significantly easier for a person that has a height of 6 feet opposed to someone 5 foot 6 inches. Geometries are always the name of the game.

Isn't this a bit like that other timeless question about length?

I use different crank lengths on different bikes, case in point my road fixie I use shorter cranks (165) to be less likely to strike a pedal on the ground while cornering while not able to stop pedaling. most of my bikes came with 170mm cranks but one bike I had for years has 172.5 and it took years until I found out they were not 170's. In actual riding I really don't notice the difference.

A friend of mine is at his optimal with a different lenght for each side. He kept on having some knee pain and found out that it was related to his leg lenght not being equal on each side. Since then his knees are good and he said that he gained about 5% performance wise.

being as a 5'8" rider. I am more comfortable riding on a 170cm crank arm as I've always used to riding it ever since I started cycling (not from childhood). If I change the length of my crank arm that will involve changing the height of a seatpost which I would rather avoid messing around with.

I'm 5'8" (with pretty stumpy legs!) and after a bike fit changed my cranks from 172.5mm to the recommended 165mm and find it much more comfortable. I can get a higher cadence and also my hamstrings, which are pretty tight, are much happier.

For years I didn't know there were different lengths available (bike shop wasn't helpful in that regard) I suffered with shin splints with longer cranks. Absolute agony. I now ride 165mm and they are perfect. It does frustrate me that it is impossible to buy groupsets with 165 though.