Recent Study-- pedal speed / crank length
 

Available, open access. My take on it is that you can specifically target one of the many variables involved but in the end the central nervous system apparently takes in all the variables and makes whatever adjustments it deems to be necessary)...

Effects of Pedal Speed and Crank Length on Pedaling Mechanics during Submaximal Cycling
PAUL RICHARD BARRATT1,2, JAMES C. MARTIN3, STEVE J. ELMER4, and THOMAS KORFF1

Interesting! Guess it really does come down to do what feels best.

Oh, it's the cranks fault that my thigh hits my belly. All this time I've been blaming it on donuts.

It doesn't really say much, other than there is little risk in trying different lengths for sub maximal efforts. The method used a fixed output at a fixed RPM. Though the power was generated differently, there was no attempt at measuring either perceived stress, or performance over time.

I can generate 240 watts at 90rpm for a period of time on a wide variety of cranks also, but it would be torture at the low end of that range. I am very tall, and experience has proven clearly; I perform better and ride more comfortably on 200mm cranks. In extreme cases like me, crank length can make a dig difference.

People sometimes try to convince me that crank length makes no difference, but I notice they are not choosing 145mm cranks for themselves, which would be proportional to me on 175mm cranks.

I notice when folks ask about what crank length they are usually deciding between 170 and 172.5 or 172.5 and 175. Such a minute difference does not make any difference. Obviously when it's 30 mm it's not the same thing.

I got rid of knee pain going from a 172.5 mm crank to a 165 mm crank.

A small difference in crank length can make a big difference in bike fit.

Changing crank length means that the saddle has to be raised or lowered to compensate. This increases or decreases saddle to bar drop, moves the saddle for/aft compared to the pedals, etc. All of this impacts comfort, power and susceptibility to injury.

We all understand that a 1 mm difference in saddle height, front to back position or angle can have a huge impact in how a bike fits. The minimum change when swapping cranks is 250% greater.


-Tim-

I'm not sure what this study purports to show? Changing the torque arm and keeping power and RPM constant would seem to be a mechanical calculation.

Usually trained cyclists tend to higher cadences with shorter cranks, possibly in an effort to retain the same foot speed that they're accustomed to. It begs the question does that go away after training with shorter cranks?

You should give a link:
http://journals.lww.com/acsm-msse/pa...sktopMode=true

This is a companion piece to a paper by the same authors from a few years ago which looked at pedal speed and crank length during MAXIMAL cycling (that is, sprinting). In that paper, they looked at crank lengths from 150mm up to 190mm. That paper was, itself, a variation on a paper written by one of the co-authors (Jim Martin) in 2001 where he looked at maximal output over a range of crank lengths from 120mm up to 220mm. All three of these studies taken together are, as Jim Martin has said to me, "liberating." He concludes that they mean you can choose whatever crank length you want, that makes you feel best, for whatever reason you want, without fear that it will compromise your power. Basically, it means if you like your cranks and want to use them, you can tell everyone else to go to hell.

I like that kind of conclusion.

True, true... albeit anecdotal, my experience on a recumbent and an upright trainer and going from 175 to 165 to sub-90 and back has a bigger impact on ergonomics than anything when you're talking about an upright road bike because for each millimeter of crank decrease, for an given amount of desired leg extension, you must also raise the seat a millimeter. My experience also was that you do not notice much of anything with just a single 20 mm change in crank length.

Agreed. I don't think it excludes the possibility that it could make a difference for some people either. In another thread, someone referred to one of those to say I was wrong to use 200mm cranks. That study did indicate the extreme high and low cranks rolled off a bit, but there was a wide range in the middle that worked fine. It did not try to correlate where that range fell in relation to leg length. It only makes sense that a tall rider would struggle more with very short cranks, and a short rider with very long cranks.

I read every study, opinion, video or whatever I could find. Open forums aside, all they could say for sure is that 2.5mm changes are meaningless for average riders with no biomechanical issues. They also warned about going too long, leading to overuse injuries. But "too long" is relative.

Leonard Zinn tried with multiple studies to show that crank length should be proportional, but failed. But the anecdotal preference of customers was almost universal praise for proportional. The best data suggests there is no optimal, but it can be wrong. If only we could convince manufacturers to make cranks in 5% increments in length, instead of 1.5%.

Hrmm. You've now got me wondering if my cranks are too long lol! I've got my bars about level with saddle. However...when deep in the drops thigh to chest/stomach clearance becomes an issue. I have no gut to speak of...

A 5mm difference in crank length should give me a full 1cm additional clearance...I bet this would aleciate the issue. Maybe?

Who knows lol

I run 165mm at 5'11", from 172.5. Can't tell any difference, except I was able to change my position fairly significantly (more aggressive).

I just switched from 175 to 172.5mm and I felt the difference immediately. To be honest, I probably couldn't explain what exactly felt different but my fit was way off to start with. I rode 40 miles with just changing the crank length and a swore I was going to swap back to the 175's. I then adjusted my saddle up a bit and slightly forward which made the next ride much better and finally adjusted my cleats by moving them back about 2-3mm which moved my foot forward to make my brain think my new shorter cranks were longer than the actually are. My ride yesterday after all adjustments felt quite good.

I was swapping out cranks as an upgrade so I wanted to experiment a little, here's an article I found from Cobb cycling that made me switch sizes Crank Length-Coming Full Circle | Bike Crank Lengths Shorten

If those are the papers that I recall, the gist was a slight improvement in efficiency for shorter cranks, and best results (from our perspective as riders) at the self-selected cadences. I remember thinking there could be training specificity going on, which wasn't addressed. But the kicker is, those "shorter" cranks were 150mm which leads me straight to: it doesn't matter, and choose the crank length you like for whatever reason.

I'm another convert. I went from 172.5 to 170mm and the difference was obvious. I tried 165 during my fit also, but I don't think I would like them all the time. Eventually I may get some 165's to play with, but my cadence went up by about 10rpm going down to 170s. Shorter cranks make it feel easier for me to spin faster with more clearance for my chest.

We do? Do we all also understand that our bodily dimensions and range of motion of different joints change by way more than 1 mm not only day to day, but during the course of a single day and even a single ride? Not even taking the effects of different clothes (chamois thickness, the number of layers, etc.) or saddle wear and tear (padding compaction, sag, etc.).

The switch from 172.5 to 175 was huge for me, and i can tell a big difference between the two. I'm pretty short, so 175 doesn't seem like it would work, but after 1 or two rides on a 175 and then going back to 172.5, the decision was easy for me. I have ridden 180's on an MTB a friend owned, and those were a little too long for me.

I had 172.5s initially. Bought some cranks that were 175s. Didn't make any difference, apart from my knees touching my stomach when getting really low. Now I am on 165s and my knees never contact my body. Apart from that it is all the same. My cadence didn't change, didn't magically gain/lose power, etc.

Also, I am sure that you could change my saddle position by far more than 1mm and I would never notice, but maybe that's just me.

:D
WOW! I never heard of 200mm cranks before, did you have them specially made for you?

say the people that have never tried a size more than 2mm up or down (if at all) :D

yes, it's performance over time that is important, and the stress you put on your body by running the wrong lengths.


For me , I tried a crank that was really too long, 180mm and it was great for a TT, but as someone here warned me years ago " never use long cranks for a long time". I didn't understand why, but what happened over time (for me ) is my Cadence went down the toilet.

As a big guy , Cadence is always an issue, and as one guy in my Club (Cat 2 road racer) said one day riding next to me, Jee'z dragan, I know your a big guy but you gotta spin". I looked down and was probably pedaling 50 to 60 pedal rev's per minute, this was on 177.5's on my road bike.

For me , 6 foot tall guy with 32" inseam 172.5 is perfect, but it's different for everybody. Whatever feels good and keeps your legs moving at a good speed is the right length. A someone else said, a 5mm difference can cause big fit issues , and IMHO if your fit is bad your power will not be good either.

that is really interesting, (and unusual based on what others have posted ), to go from 175 to 165 with no change in cadence or perceived " feel".
What is your body type if you don't mind me asking? I'm guessing lean with low body mass index and a naturally high cadence rider ?

Yes, I am fairly short at 5'6 or 5'7 and weigh ~145lbs, so lean although not crazy lean. I do seem to hold pretty high cadences for often than not.

Even in the 70s is considered spinning (whereas in the 60s is 'pushing') but compared to the pros who spin like tops in the 100s, if you're like me, even the 90s doesn't feel natural. Assuming a percent-change in crank length translated exactly to rpms, a 'spinner' going from 175 to 165mm cranks would still be spinning at a sub-80 cadence and might just gear down to get back to the 75 RPM if that is what felt most comfortable (which would translate to more power at a given RPM which is what you'd be hoping for and why for some, trying shorter cranks seems like a good bet). A 75 RPM'r can experience comfortably spinning like a pro (~90 RPM) but that takes going to, e.g., 145s.

consider yourself fortunate
I'm always a little jealous of guys who can do that, most of the guys in my club ride like that, about 90 rpm. :( They're Just zinging along , while I'm grinding and pushing and sweating buckets :cry:
I've gotten better though, today I was in the 70 up to 80 range, which is good for me, AND my knee's, hips, and beat up feet :)

75 is not bad, any higher and I get winded, probably dirt poor VO2-max, so I naturally will shift to a bigger gear and run more anaerobic. This works OK for cat 4 crits, Time trials, and spirited club rides but I don't think this riding style will take a person much further than that. There's always exceptions of course
The other bad thing about riding towards the anaerobic side of things is recovery takes a lot longer, at least for me.

It was in interesting experimenter though, and I urge people to play around if you feel like something isn't quite right. The 177.5 SRAM Red cranks I had, bought new for $250. and sold for $100., not the end of the world