Does Crank Length Affect Your Cycling Performance? The Science
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- čas přidán 27. 03. 2020
- Does your crank length have an impact on your cycling performance and how do you determine the optimal crank length for you? I go into the science as well as discuss how leg length affects optimal crank length and how changing your crank length can affect your cadence.
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The studies I used in this video:
www.tandfonline.com/doi/abs/1...
link.springer.com/article/10....
link.springer.com/article/10....
www.nrcresearchpress.com/doi/...
www.clinicalbikefit.com/wp-co...
shapeamerica.tandfonline.com/...
www.tandfonline.com/doi/abs/1...
www.sciencedirect.com/science... - Sport
Hey you mentioned me!!!! Thanks
I'm 5'6" and always had 170 or 172.5 (what came on the bike). after decades of cycling and knees getting progressively worse, I finally special ordered a 165mm crank. it really reduced my knee pain. Crank length might not affect peak performance, but it will alter your bio-mechanics and might reduce the strain on your joints. definitely worth experimenting.
Definitely agree with this. Ex-competitive skier with ancient (mid 80's) ACL replaced right knee (also scoped several times over the decades), lots of arthritis - no more repair is possible so next step down the road is knee replacement. A few years ago I got an indoor trainer that I set up identically to my road bike with the exception that it had 170 cranks. It was amazing how much less knee pain I had when indoor training vs outdoor. So I decided to change the cranks on my road bike (from 172.5 to 170). When you have compromised cartilage or arthritic surfaces even tiny differences can make a big difference in comfort. With slightly shorter cranks, my knee is less extended at the bottom and less flexed at the top. For whatever reason, this now keeps my knee more on the remaining cartilage than aggravating the arthritic surfaces. I can now cycle long distances again, and go multiple days cycling without any knee pain. Definitely worth experimenting if you have bad knees.
This!!! I was expecting the video to cover this scenario and others related to crank length and bike fit, body and joints injury prevention. I have had knee issues for the last 5 years or so, moved to 165mm cranks and it has drastically reduced the knee pain I feel. Pair that to actually keeping an eye at cadence and I can produce more power and be safe fory joints!
How about saddle position and clip position on shoes?
@@umaxi96 yes I was always adjusting those too trying to get the perfect most pain free position, but it wasn't until I switched to the 165mm that I was able (along with new saddle and toe position) to really dial it in. It has to do with making the distance from max top to max bottom smaller so there was less extreme bend at the top of the stroke for my shorter legs. With the 165mm my knees were 10mm lower (less bend) at the top of the stroke.
Interesting. I’m 5’6” as well and my 175mm cranks are driving my knees nuts.
Hey, Dylan! At 2:40 you said something that really caught my attention. You mentioned that a change in saddle height can make an 8% change in power. How 'bout doing a video analyzing that? I would really like to know if my saddle is too high
Stephen Starks +1
@@markstevens6887 +2
Stephen Starks +3
+4
+5
According to this study, If I want to keep my 172.5 mm dura ace crank arms, I must shorten my legs by 2mm
🤣🤣🤣
You can probably try a cycling shoe with a thinner sole
Go skydiving that shortens people if they land hard too many times
Most dependable, accurate cycling info on YT. Thanks for successfully avoiding the "Lets just throw some content out there so we keep getting hits" syndrom. MUCH appreciated!
tomorrow GCN will have a video on this topic
meanwhile, on GCN: how to clip in to clipless pedals... AGAIN
But you get all those British accents!
Or how to watch a race like a pro. Talk about good timing
@@mileshall9235 And we get marketed bicycles with out-of-round bottom bracket holes! What more could we want?!
yeah its youtube's way of directing us to "properly controlled content" no offence to GCN, certanly not the hosts but its about $$$. my kids carseat was made by essentally cannondale(parent company)
Haha, and the only difference from the first two clip-in videos is that someone launched some new stuff they want some cool advertisement for!
At 6'2 w/33" inseam, 165 is my fave across all disciplines. Good cadence on road/gravel, and maximum clearance on MTB. Great vid!
I am the same height and my favorite is 165 to 170 but I will not go over 170. Its awesome on the MTB to go shorter, you can hit those higher peak powers quick and accelerate better in tight and technical terrain.
And yet another question thoroughly answered! Thanks, Dylan.
The man who never blinks. Never flinches and always come with strong solid research to back up that unblinkinging profile. Thanks for this. I’ve always wondered about this being 6’3” tall.
Great vid, as usual, Dylan! Thank you for all of the well-researched data and thoughtful analysis!
Astounding! A bike channel that actually refers to different sources of research. Well done and thank you!
Dylan, congrats for the brilliant research and thank you for sharing such a useful information !!!
Finally well made video on the topic. Thanks mate!
This makes complete sense to me. Due to a knee bending issue I went down to 115mm cranks (yeah, like 4"). I have no problem keeping up with any of my cycling buddies whatsoever. My cadence is higher however, the actual foot speed is lower as the peddling circle is much smaller. My times up local climbs from 20 years ago are about the same even though I'm 68 now.
115 mm cranks? custom made? never heard of any pro cranks this short
Great info!!!!!!
I ran an [unscientific] experiment some years back where I tried riding my mountain bike (the same bike) on the same routes (both road and offroad) using 170, 175, & 180mm cranks. I noticed the same effects on cadence that you've mentioned. I also felt that I generated less torque (like when accelerating out of a corner), but a higher RPM (like when riding fast down a straightaway) with the 170mm cranks than the others (so better top-end). Because of this I found myself sometimes selecting a gear lower and riding at a higher cadence to get my best performance.
On the flip side I felt that I could produce noticeably more low-end to mid-range torque (to put it in automotive terms) with the 180's but at the expense of top-end RPM. This was very good when that extra grunt was needed to get up and over punchy climbs, accelerating out of slow corners, etc. But because I felt that my top end cadence was somewhat limited I found myself shifting into higher gears earlier (instead of "winding them out") to compensate and take advantage of the greater torque at lower RPM's. Maybe it was my imagination but the effects and differences felt very real to me.
Hi Dylan, great research and video...keep it up 👍
Maybe it would have been worthwhile noting in the video that shorter crank length could be beneficial in aerodynamics on a time trial bike and for “opening up the hips” on a triathlon bike.
From a medical point of view, if you're old, this has been my experience: czcams.com/video/CQvLIyOiYGs/video.html
Great video Dylan. When I rode track, the key advantage to shorter cranks was less pedal strikes on steep banks at slow speeds
Great work, Dylan. Thank you.
I've tried to educate myself about this topic multiple times and seemed to always find conflicting information. This video straightened it out for me, thank you!
excellent video Dylan. much appreciate the efforts
Thanks for making this! I've been debating whether or not to switch from my usual crank length with my new groupset, but now I think I'll probably just stick to what I'm already using. I think that one of the most important factors (and this has always been the case) is considering pedal strikes, which is really only an issue in specific scenarios anyway.
Excellent video and just the primer I needed on crank length!
Exactly what I was looking for. Thank you!
I usually don't comment about my cycling experience... but this hits a huge part in my cycling experience... First, I think its individual preference and can go either way... for my experience, I'm 5'3 or 160cm tall, I started with 170mm crank. I built an Allez with 160 crank, and kept my Ridley Helium at 170. I noticed a drastic difference. I noticed the 160 took more pedal pressure on climbs than 170 (makes sense with how torque is generated). I then tried to see if my sprints were better with 160 (Just like the video concluded, higher rpm, optimal power output)... and they were. I settled back for 170, cause real world riding have inclines everywhere and I felt my sprint gains weren't advantageous enough than the lost in climbing torque during my rides
or... just fit lower gear ratio with the 160.
You produce less torque but can spin (and prefer to spin) faster. So dial down the gear ratio.
@@Hexsense I actually did that too, I went with 50/34 on the 160 and kept 52/36 on the 170... the gearing was still not enough. Maybe with this new Sram AXS, 46/33 paired with 10-33 cassette, maybe... but for the price...
What gearrange are you in, and what gears do you have?
@@mreyes2633 change from 170 to 160 reduce torque by 5.9%. Changing from 36 to 34 is 5.6% lower gear, which is pretty close. One more tooth in the cassette would overcompensate it by many percentage.
Once you have sufficient low gear to reach comfortable cadence, torque would not be the limiting factor anymore. It shift back from torque to power as the limiter like most of other situation.
@@Hexsense ok cool, torque and power are directly proportional as well as rpm... check this:
Power = torque * rpm
Given a steady pedal pressure....
170 crank > torque than 160 crank
If a rider can max spin a pedal at 130 rpm both 170 and 160 pedals... 170 has > power than 160....
Which isn't real world case cause I can max spin a 160 crank > than a 170 crank...which supports my finding and the videos finding that shorter crank can produce more power...
What I noticed, was with reduced gear with 160 at 50/34 chain ring, I'm still producing slower speed up inclines.
50-28 gear (160) vs 52-28 (170), the 170 gave me faster climbing speed given 90 rpm for both.
It makes sense for track riders, cause there's no incline in a velodrome. I've invested enough money and tested as objective as I could to understand that I'm better off with 170 than 160 based on real world riding.
Great timing...I was just wondering about that the other day!!
For triathletes / people spending time in tuck / aero position, shorter cranks are often said to help, as they constrict breathing less (you don't get you knees up your chest so much). Now whether there's a study to show that, idk. But if it subjectively improves comfort, then it's probably worth it.
Hey Dylan. I am paralyzed and ride a handcyle. For me I found using a longer crank arm gave me a little more torque, but it also caused me to use a higher gear because I couldn't spin at the cadence I like. Great video!
My girlfriend said crank length matters
😝
She told me it was girth
Yep, she told me that she likes my longer crank.
She's just messin' with ya, eh.
@@richardharris8538 lol
with a longer crank arm your foot has to travel farther and faster to produce the same cadence, this fact may explain why preferred cadence goes up with a shorter crank because the speed your foot is moving might determine your preferred cadence
Basically what I say above but you did it with 20% of the words. It does explain it, along with preferred resistance.
But there is also another consideration - heart rate.
With divergent heart rate and cadence the perceived effort can increase.
I worked it out one day and to have the same leg speed with a 180mm crank and a 172.5mm(I think it was that one I was comparing it to) the 180mm crank needs an RPM of 95 while the 172.5mm needed 100 RPM to have the same leg speed
Hey Dylan, great stuff! I sat and lugged at a very slow cadence for years; like in the 70's. I virtually never stood, even in XC races. I also sat super high all the time, very far forward on my road TT saddle over top of the BB, as I could get super low with the dropper post when I got scared! But on Gerry Pflug's suggestion I moved from 175mm to 170mm. The different was huge! I found I could spin faster, stand more, and lower the seat as well. It didn't hurt as much to spin at a lower angle, something I could never do at 175mm. I also had more clearance. I think the only drawback is you end up raising your centre of gravity when standing, by about 2.5 mm,. I'm not dead sure on that, but it is because the pedal at the lowest point is a bit higher off the ground. All in all, the experience has always made me want to try a 165mm crank, but I never have! Even with the 170mm my cadence is slower than than everyone around me. I'm comfortable I think around 80rpm; but frankly just don't have a lot of data to know for sure as I never measured it racing.
Hey Dylan, love the channel. I'm an older guy that does not race just loves to ride. My wife, who pretty much won't touch a bike loves to watch also. We wait each week for your new upload and put it up on the 60 inch screen! Never disappointed. Some times I'll start out a sentence when speaking to her. "Dylan says..." and you really have taught me a lot. So thanks! It'd great to have you follow me on Stava. Wishing you success going out on your own. God speed.
Well, that’s a surprisingly interesting finding!
Two things that were missed:
- As using shorter cranks indicates a higher optimal cadence, then gear ratios also should be changed - shorter cranks, higher cadence, lower gear. As well, of course, longer cranks, lower cadence, higher gears - for the same speed & effort level.
- Higher cadence makes it easier to react to speed increases in group riding. To match a group acceleration, it’s more effective to spin up than it is to mash the pedals at lower cadence (& higher gear). For one thing the pedals are coming over the top sooner at faster cadence.
Also, what’s the data on knee (other joints too) injury related to cadence at the same load (wattage)?
it being "more effective to spin up than mash" is making some assumptions about what's ideal for the rider. If I'm doing 90RPM on my 180mm cranks (typical for me), and want to speed up 10% to match a group acceleration (99 RPM), that's not any harder than if I was doing 100RPM on my 175mm, or 130RPM on my 165mm, ans speed up to 110RPM, or 143RPM respectively.
Anecdotally, I get sore knees when I do longer rides on shorter cranks, so the seemingly conventional wisdom of shorter cranks being easier on the knees is definitely not always true. That said, I'm tall with very long legs, and already ride with a relatively fast cadence most of the time, so what's better for my knees is probably very different than someone who's short and naturally mashes at a low cadence.
While I'm likely better off spreading out the power over more of my comfortable range of motion (reducing force) at the same power, someone short who's pushing the limits of their range of motion is probably going to benefit from bringing it down to something more reasonable, while maintaining their power through a higher cadence.
@@nwimpney Good point & well-said. Indeed, it would have been better if I had said something about cadence being relative & so for each individual spinning at the higher cadence of their comfort range in order to better stay tight in a group. Right?
Thanks for another informative video.
thanks for the science article review, it helps a lot ^^
Female, 5’5” tall, long femurs, 155 cranks. That was one of the profound changes I made to my fit about 1.5 years ago.
I always had a pinching on the right front of where I contact the saddle. After zeroing in on a good, low saddle height for myself, I visited my fitter and his rig can adjust crank length. As I rode, we shortened down from my 170s and 155 was the magic number that removed that pinching. It was the length that created pelvic stability and a pressure down on the whole saddle through the entire pedal circle. I had never experienced pelvic stability like this before.
Essentially, anything longer than 155 resulted in the front sides of my pelvis lifting as my leg came over top of the pedal stroke.
I had lived with saddle sores for 11 years before I got my bike fit + crank length sorted.
what if u went to 145mm? maybe u would be able to remove spacers and go lower?
@@Dralbastaki less crank length creates higher seat posts
I’ve wondered about this - another great summary to put it to rest. Would be great to see a video of general body form/pedaling form... some tips for generally more efficient riding for those of us who haven’t ever had a coach or physio watch us ride on the road to offer tips we may not notice looking down.
Great video Dylan, Thank You
This is well put together. My takeaway message is that if I change from 172.5 to 165 then I'll finally be able to use my aerobars properly (due to higher saddle) - well that's the plan! I just have to see if I'm comfortable and generating my normal power with the changes.
Thanks for vid ..great presentation ..you made it all clear
As a triathlete doing Ironman I am looking into 165 to open up hip angle
As a semi-fat non triathlete: what does opening up the hip angle entail?
Jesper Andersson When on a triathlon bike (or drops on a road bike) you are put in an aggressive position, where the longer the cranks the closer your legs will get to your chest when pedaling. With a smaller crank length the angle between your back to pelvis to knee is not as extreme, thus the term opening hip angle.
I use 162.5 on my triathlon bike. It helps immensely in getting aero.
I am 5'11" and I ride 165s. I like to spin, it helps me spin smoother. It keeps my knees and my hips much happier then 175s or even 172.5s. I can get into more aero position because of the raised saddle height. I actually would consider going even smaller if I was going to replace my cranks again. On my old TCR with 175s my knees would be pounding my chest if I was in the position I can ride now.
A bigger chain ring and lower cadence with the shorter cranks works perfectly for Ironman. John Cobb has done heaps of work on this topic.
Good vid ! A subject that's been re-hashed over & over but it is important! During the last 25 years I have tried every length in the book, made my own 180mm with D.A. Octolink, etc. MTB finally tought me that 175mm were the best for me. At 5'9" my imseam is almost 34". It'all about comfort level at the top of the stroke, bottom of the stroke is easy to deal with. Also, longer cranks are more manageable with relaxed seat tube angles (for me!).
Thanks. Your findings match what I've learned as a kid, riding adult sized bike, pedalling through frame. What matters is - cranks shouldn't fall off BB spindle.
Could you make a video about: the benefits of training/living at altitude and what difference does it make.
?
I'm 71 years old. In the past several decades, I've used 165's to 180's for extended periods. I was 6'3" when I did all these changes (I'm now 6'2"). Thanks to the U.S. Army, I learned that my leg length is disproportionately in my femurs. That coupled with size 48 shoes, I'm pretty far out on the crank compared to most. I liked 180's but my knees didn't. I've been on 175's for the past 20 years and it works. Where your leg length is and how long your feet are is more important than just an inseam number. All said, ride what's most comfortable.
Interesting !! . . . I've just changed down from 175 to 170. I decided to do it as I felt a 'dead spot' when peddling from around the 11 o'clock to 2 o'clock position, the change seems to have improved my perceived peddling action and making riding easier and more efficient . ..
fasdiablo what is your Height....currently im using a 175mm crank...it's hard to spin fast
Very helpful thanks Dylan
1:43 Good to see Bike Fit James.
Great video!
I am under the impression that the recent movement to shorter cranks in the tri world has to do with the reduced air buffeting from shorter cranks rather than an increase in power production.
An analysis of the aero aspects of short vs long cranks would make a very interesting video!
Great video! Information was very helpful as I was thinking of changing my crank from 170 to 175, as my intent is to use my MT bike more as a cross-country bike (i.e., riding more on non-technical trails), as I was thinking that this would help increase my pedal efficiency. I am 6'2" and prefer riding through the woods on long trails, but still have the bike to handle any bumpy type single trail, but was concerned that if I went to a 175 that this would increase the chances of a pedal strike. Most likely will stick to 170. Thanks again for the great video!
I am 5’4” with a 26” inseam. I went to a shorter cranks 155cm and my decision was not for power or cadence it was for comfort. Let me explain. When you are vertically challenged like I am and the manufacture puts 165cm/170cm cranks that now means I have to lower my seat to be fitted properly;however, now at the top of the pedal stroke my knees felt like they were coming to my chest and they were. My legs would hurt. It felt like I was doing high knee exercises for 30 miles, so I started looking into crank length and settled on 155cm and my legs felt great from day one. Think about it.
I'm 5'2" and ride with 165/170 on my 2 bikes... Where did you end up getting 155? And how much did you raise your saddle?
Chris I have Cobb and Vision TTiMAX
@@RoyDeWeese i am 6 3 i think and about and over 34 inseem not exactly sure how much but i have the same problem with my knees hitting my chest
Love it! Thanks.
thanks so much!!!!!!!!! that cleared my mind good
That was very informative. Thanks. I've found from my own experience that it really boils down to fit. With a good fitting bike you can be most efficient. Even if it's a perceived differance having a little more confidence might push you just a little further.
Thank You. Good research. I’ve been running 175mm for years (32” inseam) on bikes around 56cm. Now that I am an old man, and In the market for new road bike, I am looking at 172.5mm as it seems my knees are getting a bit sore on rides where I am pushing more power. I was worried about going down to the smaller crank length, but this video tells me - it!’s no big deal for 2.5mm delta.
Fantastic !!!
Best 10 minutes yet , BHD take note 🙂 !! I think originally track rides used 165 mm so that didn't hit the pedal on the banking , and 175 on MTBs was because they thought u needed extra leverage to smash up the short super steep climbs
Bit of an old video but I changed from 175 to a 165 crank recently (I'm 5'7 with a short inseam of 28in) and was surprised with how much more comfortable it was, particularly when standing. Didn't notice any tangible differences in power but I'll take extra comfort any day
Thank you! I've been trying to find info on this subject after a few friends swore that dropping down to 170s made a world of difference to them. I didn't want to spend the money on new ceramics to find out if if it's all in their head or not.
Awesome video Dylan. Some of my riding cronies are obsessed with crank length and wholesale swapped out a bunch at the same time. Kina had me thinking it was vendor conspiracy to get people throwing away perfectly good stuff for something "new & improved" LOL
I've never paid much attention to using anything other than 175mm on all my rides. I messed with 180mm's on single speed 29er's and found that it felt more efficient on certain geometry bikes over others. Nothing too dramatic and with the more modern geometry designs with lower BB height, longer cranks can lead to more pedal strikes.
Dylan, I looked at this a lot about 3 years ago. I think the answere is disciplin specific.. tracksters use short cranks. In my case, I was riding 175 and had issues with both my knee and hip angles when on the drops. I actually bought second hand cranks from 165 upto 175 at 2.5mm increments. I settled at 170, 167.5 was prob the best but it was marginal on how it felt, and I couldnt get thrm in the brand/range I wanted .
Here's the thing though, its only a 5mm difference, but as it is shorter it alows the saddle to be lifted 5mm for the same leg extension angle, the benefit comes at the top of the stroke as your saddle is now 5mm higher and the pedal 5mm lower. This really helps both your knee and hip angles. Effectively like raising your original saddle set up by 10mm, which eases knee and leg angles particularly if you are on the short side of the mean. For longer distances this made a massive difference to me. It wasnt about how much power it was about comfort and ease of power for me.
I will be glad to tell you my results and why I ended up sticking with this
The timing of this video couldn’t have been better for me thanks. I sized down one size on my new bike and kept the same crank length and discovered a new phenomenon for me - toe overlap. I may need to drop crank length if this toe overlap becomes a problem, but so far I can’t tell much difference otherwise.
Ryan Wayne I use a CX as a winter training and commute bike, that has terrible toe overlap. Changing to 165 was worth it just for minimizing the overlap. Still can’t use mudguards on the front wheel though, but that is less of an issue.
My bike is also a CX frame built into a gravel race bike. I am considering going to 170 mm from 175 mm to see if this eliminates the problem. Thanks for sharing your experience
Just run a bunch of toe out to clear the tyre. I'm sure your knees will be fine. (joking of course)
Hi Dylan, great video as ever, crank length can be important for knee angle at the top of stroke, especially short riders. Shorter cranks can increase the angle to more than 70 degrees, less than this can cause injuries.
Great video. I am 5'10" and just built a new bike with 160mm cranks. I went that short to resolve a biomechanical issue particular to the shape of my pelvis as diagnosed by my bike fitter/physical therapist. Despite good flexibility, can get palms to floor,II would get low back pain in even an endurance gravel position.
For me, taking the chance, going that short, and opening up my hip angle made a huge difference.I can make more power, longer and more comfortably, in a more aero position then ever before.
But I was comfortable giving it a shot because they studies say there is basically no risk in losing performance in going short. - my PT basically said the same as Dustin here. So I think one thing, is if you think there is a biomechanical advantage particular to your body, there is certainly no harm in going shorter.
I ride a lot of gravel - and one nice thing about the short is all the pedal clearance. The only down side for me has been lack of selection. Rotor and Sugino are the only game in town that short with gravel gearing available, Favero Assioma pedals hacked with xpedo MTB pedal bodies for power.
Really cool, I used to do a fair amount of distance on unicycles, most with 29” or 36” wheels. For unicycles, crank length is super important. It’s common to be able to find unicycle cranks from 115mm to 175. Because they’re low geared and fixed crank length is almost like changing gears. For distance on road or gravel 125-135mm cranks were ideal for spinning and 140-150mm were great for power off road but not as spin-able. 175s would wear me out quickly and definitely were not as smooth. I ride Singlespeed a ton, and I think that crank length is more important than with geared bikes. I like to spin, I think probably 160 would be amazing for my Singlespeeds.
^^^ this should be a pinned comment! 👍
It's worth keeping in mind though that because of the lack of gearing, you're having to use shorter than ideal cranks just to allow a high enough cadence. I run cranks around 100mm on my unicycle with 700c 25mm (typical road bike) wheels to allow a silly high cadence just to be able to ride at jogging speed.
So, in the case of trying to go fast on unicycles, it's not so much choosing the "ideal" length, as it is choosing the shortest cranks that you can manage to balance on. (If you're not smooth, you won't have enough torque to recover if you get off balance, and you'll crash)
Pretty much everyone, including short people, are using cranks that are way too short for them on the unicycle. It's just a limitation of being direct drive.
A good comparison would be measuring your power output with different crank lengths while leaving the bike in its lowest gear. Most riders will make more power the shorter the cranks are, because they're almost purely cadence limited, not torque limited.
Much appreciated!
Thanks for this. I’m going to run 165s on my fixies and 165s on my mountain bike, because pedal strike is my greatest fear, and apparently it just doesn’t matter.
Dylan, great video as always. I'm on 165 mm cranks since I developed hip FAI issues and I love the shorter arms. Even if I'm 6 feet high! I also would like to suggest a video: what about gross efficiency, heat balance, termal expenditure and, why not, how this all affects different riders on indoor training? I'm on an assumption that riders with lower efficiency will have lower performance indoor (in comparison to outdoor) than riders with greater efficiency, on same conditions. But I'm still looking for scientific evidence and other researches for that.
In terms of the physics, increasing the crank length is somewhat like making your back ring slightly bigger. You move further to get the same input, therefore the resistance is less. Because we have so many options for resistance with gears it's not easy to feel the slight change. However if you have two single speeds with the same gearing, but with a difference of 10-15mm in the cranks, you can feel the shorter cranks giving you more resistance, as though you shifted up one gear. The reason the 165'rs were doing more RPM's was they had to downshift to attain the same lighter resistance as the 175'rs. The velocity of the feet was the same even with the higher RPM of the 165'rs - if you imagine the distance around the circle. Pi x diameter = circumference, so if the two cadences had stayed the same, the feet would be traveling 518 mm to go around with the 165s, 550mm with the 175s. So more torque with the 518 to get the same distance out of the wheel. Inversely, to cover the 550mms the 165s need 1.06 revolutions compared to the 1 revolution for the 175s. So 6% higher cadence. Simple math.
Another way to imagine this is if you had a bike with two chains. A ring in the front pulling a second ring in the middle, directly attached a third ring with the second chain, which spins the fourth ring on the back wheel. If that second ring gets bigger, what happens? (just like your bigger ring typically on the back wheel) -- less resistance. Your legs are that first chain and the cranks are that second ring.
Hope this doesn't sound convoluted, it's actually quite simple. Purely ratios. The absolute simplest way to imagine it is with no chain, and your cranks directly spinning the back wheel . Longer cranks would basically be the same as a bigger back ring.
Of course this doesn't address leg length, preference or performance. Just the Newtonian side. Hope I didn't take all the fun out, LOL
This really shouldn't even be a question. Anyone who's ever had to loosen a bolt using a breaker bar understands the concept of leverage. The crank arm is doing exactly what a ratchet does to a bolt - applying twisting force. The longer the bar, the more force is applied. A longer crank arm is going to provide greater leverage, and thus each pedal stroke will apply more force than the same stroke with shorter arms. Yes, shorter arms let you spin faster, but why would you want to? It's not like you're gaining anything; a rider with short cranks will have to spin faster in order to match the speed of a rider with longer cranks, so basically shorter cranks just means you have to work harder to get the same result.
The only reason a shorter crank length is desired is on a MTB, where ground clearance becomes an issue. Downhill bikes for example, will likely have short cranks because gravity propels them most of the time. An XC bike on the other hand, uses longer cranks because a great deal of it's time is spent pedaling. My XC bike has 175mm cranks. I wouldn't dare go shorter - shorter arms means I have to work harder to apply a given amount of power.
Regarding leg length, that's not really going to be a factor provided the rider has saddle height set optimally. Short leg or long leg, a longer crank arm is still going to offer more leverage. The distance between the center of the crank axle & the tip of the crank arm is going to be same, no matter the size of the rider's leg. Thus, the number of strokes needed to produce X amount of speed is the same regardless of leg length, because the circumference of the pedal stroke is the same. Provided the rider has their saddle set so that each pedal stroke almost fully extends their leg, they will apply maximum power on each stroke.
It will not effect the bottom of the stroke if a shorter legged person has the longer crank. (Assuming the seat height is set correctly as you point out.) But it will certainly still effect the top of the stroke.
Leg length is another lever size, and the difference in angle between tibia and femur could be greatly affected, depending on how short of legs we are talking about here!! imagine yourself riding on a 200 or maybe even 240mm crank, how much more bent your knee would be at the top. Once again, that angle is part of the leverage equation.
@@sixstanger00 you're forgetting losses to friction. Pushing big cranks means more chain tension and this definitely affects mechanical efficiency in both chain and bearings in the bottom bracket and rear hub. It's never simple, and there's always a trade-off.
@@sasquatchrosefarts The crank arm length will not change the amount of friction on the chain/hub, because the chainring is still the same diameter.
The chain engages with the chainring, not the crank arms. A longer crank arm simply provides more leverage to rotate the assembly easier. But the chainring and chain itself will experience the same amount of friction at 80 RPM, regardless of crank arm length. The only way you can increase friction at the chainring is by increasing it's diameter and thus adding contact points between the chain/teeth.
As for chain tension, the weight of the bike/rider is fixed, so the drive wheel will require a fixed amount of energy to spin, regardless of arm length. The longer arm, just like a breaker bar on a bolt, allows you to apply that energy _easier._ But ultimately, the chain will experience the same tension in a given gear selection, because regardless of the crank arm length, the _weight is still generally the same._
A longer arm doesn't mean you apply *_more_* power, it just means that applying X amount of power on 175mm cranks will be easier on your legs than 165mm cranks.
@@sixstanger00 more torque and lower rpm is more tension on the chain. Get off the meth bro
Height 189cm. Inseam 88cm. My first bike came with 165mm cranks. I found I was constantly raising the saddle to get comfortable. Switched to 175mm and have been riding 40+ years comfortably.
Did you find anything about ultra endurance? I heard going shorter reduces the movement in your hips therefore reducing potential problems in 1000+ km races. Is there any basis to this statement? Cheers mate!
It also increases the force at a given cadence and power output, (or increases the required cadence at the same force and power output)
so there's no free lunch.
If you're moving your hips more than is comfortable for long rides, shorter cranks might help.
If you've got long legs and you're already underusing your comfortable range of motion, you're going to be increasing force on your knees, or increasing your cadence to maintain the same power, so you might make things worse.
It's really about fit, and unfortunately it's not something that can be easily adjusted, so there's no way to experiment cheaply, so most of us are stuck running whatever comes with our bikes, whether it's ideal or not.
Using the SRM formula to work out its slope uses crank length its less force required with a longer crank. So in that sense if you have a bike fit for a longer crank and have that range of movement is fine it would be more beneficial in ultra-endurance events
As always, I agree with the Backward Cap Dylan! :D But, jokes aside, I also agree with your final comment that crank length should be considered more from the bike fit perspective. Any 40-something with a pronounced beer gut would appreciate shorter cranks for opening up the hip angle and preventing the knee from kicking into the belly. ;)
A few questions: 1) were the sprinting power tests you referenced done sitting or standing? 2) Where they fixed gearing (track) or shiftable drivetrains? 3) Have there been any studies on optimal flexion of the knees in power studies or perceived effort?
Thanks, Dylan. Always thought provoking. Your summary at 10:51 does not seem in line with your earlier summary of the shorter crank length and sprint power, rather your earlier summary suggested the athletes reached their peak power faster, correct?
For track and other fixed hear riding - shorter cranks also means you can corner as faster speeds and not strike your pedal (since you cannot stop pedaling).
Just dropped to 165's from 175's after my bike fitter recommended it. I'm very happy with the change so far. I'm 6'1", so you'd think 175's would be ideal, however, arthritis in my hip causes hip flexion issues, so it made a HUGE difference to drop to smaller cranks. I only have 100 or so miles on the new cranks, but so far, so good. I'm way more comfortable on the bike after the adjustments were made. Can't believe I waited so long to get a proper fit.
I'm 180 cm, 81 Inseam, had 175 mm, switched to 170 mm, night and day difference, I don't care so much about the performance I mostly care about comfort during long rides, after I changed I didn't have knee or muscle pain no matter how long I rode my bike and trust me when I say that I tried all saddle heights from too low to too high and everything in between on 175 set up, that is because you can effect the low point with saddle height but the highest point is affected by the crank length 1 major thing I noticed is that before the change I would get the rocking out of the saddle sensation like my hips are jumping during high cadence intervals, now those are completely gone and my body is telling me that the change was good. I was inspired by the Neill Stanbury bike fitting videos on Cam Nicholls channel some cool stuff there.
Interesting topic!
It's easy to understand that there must be a relation between crank length and leg length. Possibly foot size also has some impact.
Apart from that a rider with more muscle mass and strength should gain more from a long crank length because it's more efficient with lower cadence when having a large mass to moving around compared to a rider with thinner legs.
Thx for insight. Interesting outcomes regarding power and cadence. This enables me to reduce the question to issues like comfort, fit and alignment, reduced likelihood of injury, perceived benefit and finally impact of and to ageing. I did like the comment re different bikes. Thus price of changing all bikes/trainers could be an issue.
i'm around 5'11 and switching from 165 to 175mm cranks wound up somehow being an amazing upgrade for me.. so much more comfortable. i think that extra comfort def comes into play on longer rides, but either way the data in this well-researched vid was actually pretty shocking
Thanks for this in-depth review. Not exactly what I expected based on personal experience but I trust the science. So not very scientific because my chainring sizes also changed but @ 5'6" and long-time 165 crank user, I switched up to 170 when I bought my GRX (48/31) gravel bike. Interestingly, on longer rides and races I noticed both knee and achilles pains I hadn't experienced before. I chalked this up to the new bike, its fit, and didn't really look at the cranks suspiciously - maybe because GRX doesn't come in 165, so I was stuck. I kept my Cannondale 165 (50/34) on the trainer and was seeing sprint power over 1.1kw easily during 4dp tests but on the 170s struggled to peak 900w at while attaining a decent sprint cadence. Last week I switched out my gravel bike to Ultegra 165 matching the Cannondale and found my interval sessions are easier to complete at higher powers and longer durations and my joint/tendon issues have not reappeared on rides over 80mi. (note - Power meter was reset to match the new crank length.) My sprint on the road now matches what I can do on the trainer. I think this melds well with the science; that we need to experiment and find the crank that allows our preferred cadence; fits our biometrics and metabolism. Now I only wish Shimano would make a GRX 165 crank.
I'm 5'11" and run 175mm cranks on my mountain bikes and 172.5 on my road bikes. I would like to try 180mm cranks to see if I can tell the difference. This was interesting. Thank you.
Great video kind off what I expected the outcome to be, so when I see a bit shorter lightweight cranks on sale for or vise versa I'm just gonna get them and not worry about the slight difference.
Subscribed! Seems like it would be a good idea to spec ultra short cranks on enduro/downhill bikes to allow for lower BBs (therefore lower CG and cornering) and better sprinting performance.
Excellent content, as usual. Thank you, Dylan.
Thank God your still making videos.
The 8% power change with seat height ( and maybe with fore - aft adjustment )
is worth an explanation , thanks
A good look at this! Regarding leg length relationship - its not really leg length that determines optimal crank length in my view but the length of the femur. So picture an engine pistons conrods and grankshaft. Thats the analogy. I was moved from 175 to 180s some 15 plus years ago by a very stute coach - ex TT specialist. It took a short time to re-establish my cadence mayber 3-4 weeks. So all of my road bikes including the TT have 180 cranks. I've never had an issue with cadence - did all my training at 95-105 - optimal power for me occured at 92-95 - for continuous power that is. As far as sprinting and track - no question - shorter cranks are better for short term power output. Sustained climbing and sustained power - i have never looked back on the move. I'm 1.89m and run a 58 top tube. Some smaller climbers use larger cranks - Pantani for example - he used 180s if I recall and he was tiny. Dont know the logic.
For Track Sprint it's an interesting one, because you have to account for the reduction in gears with the same leg speed "rpm". Standing starts are better with a longer crank (higher moment), and shorter cranks are generally seen as better for spinning once at speed.
I concur with the conclusion. I can feel a bike-fit difference between riding my gravel bike with 175 cranks and my road bike with 170 cranks and have been saving up to swap the gravel bike cranks to something smaller. When riding my XC with 175 cranks the bike-fit differences are not noticeable because the whole setup is completely different. Glad to learn that none of the crank length changes will actually have any meaningful impact on my measly power output.
Bro I love your nerdy videos
After running 165 on my track bike and 170 on my other rigs, switching to 175 was soooo crazy at first. I felt like my legs were flinging off my body! However, switching to 175 was necessitated by moving to the Appalachian mountains. My spin is just slower (rare to go over 160 rpm) and having that extra length has seemingly helped me with the miles long 4-6% climbs. Plus I'm 56 now, and I don't do anything fast, just longer. The longer length seems to help, but that could just be the placebo effect.
Very well researched. What I got out of this video is that 170mm is the sweet spot for the majority of riders, and you should only go longer or shorter if you have a specific reason to.
From 2:15, I know a male rider who use 150 mm crank length not for a power production nor a bike fitting reason. He use it just to have enough saddle height to avoid seatpost hitting with reservoir tank of his Specialized Shiv Disc (2020). The crank is Rotor Aldhu and I believe Rotor make this Aldhu crank range from 150-175 mm for a good reasons.
Yes, I went from 175mm to 170mm crank on my mtn bike and I find about 80% less peddle bang on rocks and I can stand and peddle so much better. I’m 5’ 10” and my inseam is 32”. The only thing I noticed was a bit more narrow stance took a little bit to get used to hitting jumps.
When I started road cycling in 2000 I used 172.5 mm cranks for 16 yrs. Now I ride 175 mm cranks & what I’ve noticed is my torque & power is outstanding, especially on climbs. I wished when I raced I would’ve used 175 mm cranks with the power & leg speed I had back then. I’m a 6 ft. 225 lb. cyclist who can beat my smaller cycling friends up most climbs here in So. California. Oh yes, I’m 55 yrs. old by the way.
Thanks for making this. I have been wondering this for a while. In 5'7 with a 30 inch inseem and i use a 175mm. With that setup my max cadence is around 200 and I usually hold around 95-105 on my rides.
Seriously? We are similar height, only half inch taller and my inseem is 32.5 inches . I find it hard to pedal 170mm...
At 200 cadence I think I'd be falling off the bike. With shortish legs and long cranks thats a crazy ammount of leg movement. If it works though thats what matters.
Going from 172.5 to 160 cranks I find my power the same, cadence higher but the biggest thing is it opens up my hip angle so I can get in a low aero position and sustain it much longer and at a higher power. I'm 6 foot tall btw.
Different crank lengths on every bike is great. Variety is the spice of life, maaan.
The main thing to focus on is setting and terrain , a longer crank will be better going up hills or on more diverse terrain , giving you more leverage to your cadence, where a shorter crank will be most effective on the flats like crits or track , I personally set up my crit bike different to my climbing bike 😁
Dylan - can you make video on saddle high effect on cycling performance ? Both peaks power and endurance ? That would be really interesting to see your educated view on subject, Thanks