ThermionicScott 

I know you can't expect the world from an abstract, but it would be nice to know what heights were represented in the study. It should surprise no one that the subjects fell into a distribution where there was a middle ground that everyone could use. It only gets interesting when you bring in the outliers.

As for the study @wphamilton referenced, I just gave it a read. By the authors' own admission, their test bore little resemblance to real-world riding, and the conclusion was that crank length made remarkably little difference in power output. That must be how 100+ years of cyclists didn't notice they were on the "wrong" length cranks.

But while we're on the subject, the general public has a real problem with interpreting the results of scientific tests. By nature, these tests are limited in scope and variable, and the authors usually admit the limited applicability of their findings. But once everyone else reads the headline, they think "Of course! This is how everyone should do it all the time!" One thing we haven't addressed in this thread is that when riding bikes in the real world, we occasionally (or more often) like to ride out of the saddle for acceleration, hill-climbing, or just to give our butt a rest. The low-gear, high-RPM riding style that suits shorter cranks most of the time doesn't work very well out of the saddle, and may explain why road riders have stuck with longer cranks. Oh, but another study said that spinning a low gear is more efficient, so perhaps we're not allowed to discuss riding out of the saddle anymore.

wphamilton

If you meant the one I referenced below, median height 179 cm. Just google the title and you'll get the full study. Leg length varied from 76 cm to 91 cm.

The study isolated investigation to one variable - crank length proportion of leg length - for a single question: what is the maximal power. We don't expect them to answer general questions. Such is the nature of studies. That's why I linked you up with the abstract and the study title, not a write-up and headline

The only criticism I had of this one is the same problem I see in most of this kind of study: they did not control for the cyclists' training.

OP should be confident of my conclusion: that there's not too much risk in his trying out a 165mm crank, and the variance is in the order of 1 or 2% anyway.

ThermionicScott 

No, that first part was in reference to the stair height study -- had a harder time finding the full text of that one. I should have been clearer.

We're in total agreement as to the nature of studies and whether the OP ought to try a 165mm crank. It just irks me when people read way too much into the results of a study, and don't take into account the magnitude of the difference or other limitations that might keep it from being prescriptive. Pardon the rants.

McBTC

...a 'low-gear, high-RPM riding style' and a shorter crank is not necessarily related. For any given gear, going to a shorter crank will increase RPMs. The higher RPM does not result from going to a lower-gear-- the distance the foot travels /revolution is less.

And, there may be no need to go to a lower gear when going to a shorter crank because the reduction in foot speed per revolution may feel more natural--i.e. efficient, such that the rider is capable of pushing the same gear at a higher RPM, which equals more distance traveled, which means more power is being generated.

ThermionicScott 

You lose leverage with shorter cranks, so I don't see how you could push a big gear as effectively. How much hard riding out of the saddle do you do on the 145mm cranks you claim are best?

McBTC

It may not work for you. There isn't a lot of research but it is interesting--e.g.,



* https://www.ncbi.nlm.nih.gov/pubmed/11417428
__________________



I am not sure what standing or sitting has to do with it but perhaps it is a factor. As I understand it, track racing involves powerful riders who oftentimes use 165 mm cranks but they do not stand on the pedals. Apparently, crank length doesn't matter so much that enough people care to spark the industry to care. Even so, that doesn't change the facts: from a power generation viewpoint, 'standard' size cranks are not necessarily the most efficient and for some 145- to 165-mm cranks may actually be a lot better for many riders than 170- to 180-mm cranks.

noglider 

No. You don't pedal faster. You pedal harder.

fietsbob

I Put a pair of 180 XT M730's I Had, On, and as a result got to lower my seat a little,
to make the bike more stop light put a foot down from the saddle , easy.





./.

ThermionicScott 

Enough with the lab studies! I want to know if you actually ride hard with 145mm cranks or not. I don't know about you, but my riding doesn't consist entirely of 3-4 second bouts while seated.

Umm, ever heard of a "standing start"? Track riders use 165mm cranks to avoid pedal strikes on the turns. They often use longer cranks for regular road cycling.

McBTC

I can only say that my personal experience does not conflict with the lab studies, as I understand them. The studies tell us, I believe, that within a range of acceptable crank lengths you probably will not lose more than 1/2% of maximal power even if you are using a sub-optimal crank length.

What that means to me is that any rider probably is free to experiment and adopt what feels right without worrying about power meters and controlled experiments-- i.e., doing what feels right probably is best.

After years of riding with a standard configuration, without knowing anything else I would conclude my RPM riding style essentially is that of a spinner-- i.e., not pushing gears in 60s. However, 'spinning' for me was mainly in the 70s-- that's what felt right: not in the 80s.

With shorter cranks I can spin comfortably in the 80s instead of the 70s and in the same gear. I interpret that as a gain where just doing what feels right also seems to be best.

Leisesturm

Interesting study, and not that I think that stair treads translate much to crank length selection, but the bolded above is an interesting takeaway is it not? It is to me, and mainly what informs my opinion that crank length selection by some complex relationship to a cyclists height, ankle to hip socket length, or any other personal dimension is a huge waste of time. Crank length probably does have a relationship to lower body mechanics but just as a wide variety of humans adapt to the unilateral decisions made by Civil Engineers and Architects regarding the ergonomics of various things in our world, and stair tread risers in particular, so also do cyclists mainly adapt to the small variety of crank lengths found on production bicycles.

I will go so far as to suggest that even if some manufacturer came out with an infinitely adjustable crank such that cyclists could simply find their own optimum crank length fairly easily I submit that 85% of cyclists would select the 170mm setting. Why, because its what we are used to. A certain percent would go smaller, mainly because they can, and an even smaller percent would go longer, for the same reason. Those going smaller would in all likelihood go quite a bit shorter than 165mm. All this is my supposition based on not much more than hunches, but the people that actually make cranks. I think they have more than hunches to go on.

McBTC

Isn't the current 'standard' just a carryover from years ago when roads were a lot different and when cars probably were not as fast as some cyclists today? If there exists some measure of 'work load' common to all riders irrespective of the conditions my guess is that it probably would be something like foot speed; and, the technology at that time probably went along with that.

My hunch is that given improvements in equipment and roads, the same effort at the legs now results in higher foot speeds at the pedals compared to cyclists of yore when the 'standard' crank length was established and became ubiquitous. So perhaps shorter cranks begin to make more sense to better direct the effort applied to the pedals, especially when you consider that the amount of leverage a longer crank arm provides when needed -- such as on a hill -- is wholly irrelevant when you have the gearing.

ThermionicScott 

Why are you so reluctant to share your crank length? Theory means nothing if it doesn't model reality well.

Leisesturm

I beg your pardon. I thought we were discussing bicycle cranks. MB's crank length is his personal information and none of our business!

AnthonyG

What always gets me is that its TALL riders who like long cranks, and yes, I would put you on long cranks too, are the most ADAMANT that SHORT riders don't benefit from short cranks!



I'm short, I've ridden 170mm cranks, 165mm cranks, 152mm cranks, 140mm cranks, 135mm cranks, 125mm cranks (I'm still going) and 110mm cranks. Whew!

I'm going to get some 130mm cranks made next as I think that will be MY length.

ONLY the 110mm cranks were really too short for me but seriously I can go faster and longer with 110mm cranks than I can with 170mm cranks.

I have done 70km+ rides with both 170mm cranks and 110mm cranks.

Long cranks make it difficult and uncomfortable to go through top dead centre. I can take off like a bat out of hell with short cranks. Seriously. You get out of the saddle and go. Its easy.

Its not about rpm. Its about foot/pedal speed. For a given FOOT speed, the rpm are higher with short cranks and slower with long cranks.

My shorter thigh length means that I have MORE force at the knee than a taller rider with long thighs. The human thigh is a reverse lever which has a longer legged riders KNEE moving at a higher speed but LESS force at the knee than a shorter thighed rider.

EDIT: Ok, I keep editing this statement as it is tricky to get you head around it. Now I'm going to say, A short legged rider with short cranks can ride at the same road speed, with the same FOOT speed as a taller rider can with a longer crank. The same foot speed with shorter cranks does mean a higher cadence and a lower gear but what we are equating is foot speed.

You have to asses the WHOLE system.

A bicycle crank is like an engine crank. (I've edited my post. I did call it a con rod. You leg length below the knee is the con rod.

What's the goal? The goal is to match the correct crankshaft to the correct engine.

A short crankshaft is right for short thigh length riders and a longer cranksfaft is correct for a longer thigh length rider.

Why tall riders continue to insist that short riders don't need/benefit from short cranks is beyond me.

Anthony

ThermionicScott 

prathmann

But you gain leverage with lower gears so it's easy to compensate for changing the crank length by also changing the gearing. Can't speak from experience for 145mm cranks, but my bikes have cranks ranging from 165mm to 175mm and I don't notice any significant difference in the ability to do out-of-the-saddle climbs as a result. My natural cadence is a little higher for the shorter cranks so using a lower gear is fine.

McBTC

True, true, I am a taller rider who agrees with you. My old hard tail Salsa had 180s. I've used 96s on a trainer. It's all good but in my experience, what is considered 'standard' isn't necessarily the best -- not for me -- not if I feel more comfortable, spinning a higher gear, at a higher revolution, simply by going to a shorter crank.

AnthonyG

Thanks. And this brings us to what I consider be be a better arbiters of crank length for individuals.

1, Comfort. An important part of comfort is balance where properly integrated shorter cranks leads to a more rearward weight balance which takes weight off your hands/shoulders.
2, Aerodynamics, shorter cranks make it easier to adopt an aero tuck.

Study after study shows that power is the same over a wide range of crank lengths so power is completely off the agenda for picking a crank length.

The same power with better aerodynamics makes a rider faster and better aerodynamics along with more comfort on a bike makes a rider a better endurance athlete and cycling is of course an endurance sport.

Anthony

bikebreak

How does a shorter crank arm mean you move rearward ?

McBTC

...as you raise the saddle.

AnthonyG

Raising the saddle is part of it but also if you design a bike frame to have most people sitting at KOPS (knee over pedal spindle), then when you fit shorter cranks to a frame, the pedals effectively move rearwards and so you need to move the saddle rearwards to match.

I don't believe that KOPS is the be all and end all of saddle placement but it is the place to start. Ideally people are able to move in front of or behind KOPS to suit.

95% of small frames have people WAY in front of KOPS which places a lot of weight on hands and shoulders. Why do they do this?

Well, when cranks are too long for a rider leaving a relaxed seat tube angle on a bike will place a rider WAY behind KOPS and the leg angles will be crazy. Being in front of KOPS makes it easier to ride cranks that are too long for you. Also, since the manufacturer can't take any more reach out of 700c wheel frames than they already do then the reach on small frames would be ridiculously long.

The combination of long cranks and steep seat tube angles just KIND of works for long enough that people don't complain on short rides. When you start riding longer distances though the combination becomes painful.

Remember, things are done this way to suit the bike manufacturer, not the bike rider.

Anthony

McBTC

Keeping the knee behind the pedal spindle becomes less of an issue as you get closer to a midfoot position. But then, toe overlap becomes an issue on short wheelbase bikes with steep head tubes.

Cyclists of yore rode bicycle shoes on traditional pedals with clips until their natural foot position was registered on the bottom of the shoe by the imprint of the pedals cage. After that, a piece of grooved aluminum was nailed to the bottom of the shoe so that the rear part of the cage slipped into the aluminum groove.

The natural foot position was more rearward in the old days (e.g., up to the 70s) than most clipless setups can duplicate. About the only change in years in cycling shoes and cleats has been a fairly recent trend toward allowing for a more rearward positon of the cleat.

McBTC

e.g., "This is why you naturally go to a mid-foot position on flat pedals. If you don’t have someone telling you that it is wrong and strapping your feet to where they “should” go most people would naturally find this foot position themselves and stick with it."

https://www.bikejames.com/strength/do...hen-you-pedal/

Carbonfiberboy 

I'm a short-legged 5'6", have 170mm on my singles, 175mm on our tandem. I don't notice a difference. Can climb at 95 cadence on any of them and stand for 500 vertical feet at a time on the singles. There are many lab studies showing many different things about cranks. In the real world, elites who can ride full custom bikes, and could have any crank length they chose, use the same crank lengths as the rest of us. Everything on a bike is a compromise. If there were real performance differences, we'd see what the elites use trickle down to the rest of us.

Here's a good discussion of the fit and industry issues surrounding crank length: https://www.stevehoggbikefitting.com...gth-which-one/
Here's another take on it: Bicycle Crank Length Implications

IMO, go with what's convenient for you. I have a 6'5" riding buddy with 180mm cranks. Works fine for him. My 175mm tandem cranks work fine for me and are what came on the bike.