Folding Bikes - Crank arm length

Has anyone experimented with different crank arm lengths?

170 mm seems to be the standard, but I have a collection of cranks I'm not using, so I've been trying out some different lengths. For the last week I've been using 175's, and hated them. Good leverage for going up hills slowly, terrible for anything else. So for comparison now I've switched to the shortest ones I had, the 152mm (6") crank that came on my Kent magnesium folder. As you'd expect, not much leverage; but great for spinning! I may actually stick with this one....

165mm Sugino RD cranks on my fixed Swift, not so much for the smoother spin, but because I think they fit me better for my particular inseam length (30 inches). Compared to the 170mm cranks I've used prior, I feel that I can pull the pedals around the stroke much more effectively with the 165mm.

Crank length really is connected to leg lenght. The best method I have heard to find the optimum for a person is to lift one leg up bending your knee and lifting your foot straight up to the highest comfortable place you can. Have another person measure from the bottom of your foot to the floor. Divide that distance in half and that is the maximum crank length you should use. Roger

Crank length really is connected to leg lenght. The best method I have heard to find the optimum for a person is to lift one leg up bending your knee and lifting your foot straight up to the highest comfortable place you can. Have another person measure from the bottom of your foot to the floor. Divide that distance in half and that is the maximum crank length you should use. Roger

Wait a sec, let's give it a try, tell me if I'm doing this right....

Okay, I'm standing on my right foot. I lift my left knee up as high as is comfortable, holding the left foot parallel to the floor. I measure the distance between the sole of my left shoe and the floor. Divide by two.

580 ÷ 2 = 290

So the maximum crank length I should use would be 290mm? :eek:

165mm Sugino RD cranks on my fixed Swift, not so much for the smoother spin, but because I think they fit me better for my particular inseam length (30 inches). Compared to the 170mm cranks I've used prior, I feel that I can pull the pedals around the stroke much more effectively with the 165mm.

I swapped out the OEM 170mm Brompton cranks for a pair of 165mm TA Specialites cranks for ergonomics - I have a 30" inseam. I had no proiblem with the 170mm cranks, but the 165mm cranks are smoother and more efficient.

Has anyone experimented with different crank arm lengths?

170 mm seems to be the standard... So for comparison now I've switched to the shortest ones I had, the 152mm (6") crank that came on my Kent magnesium folder. As you'd expect, not much leverage; but great for spinning! I may actually stick with this one....

Hello Rudi.

Mike Burrows, a UK bicycle designer who at one period worked for Giant, has. He has an article in this quarter's edition of "Cycle", the UK journal from the CTC organisation about crank lengths & he quite likes shorter ones like you've tried. I'm still looking for some to try on our bikes.

Here's an article by Peter White with information on sizing cranks.
http://www.peterwhitecycles.com/fitting.htm

You need to lift your heel directly verticle so you are not over lapping you leg muscles. You are basically kicking yourself in the but. Not out in front of you. You also need to be comfortable in that position not with your leg muscles in tension. I will measure myself and see what I get. At 6' 0" and doing as i said I measured a touch over 340mm. Divided by two that is 170mm which is what I use on most bikes. Roger

I'd like to try out some supershort cranks myself. Anyone recommend a good source?

I'd like to try out some supershort cranks myself. Anyone recommend a good source?
BulletProof cranks sold at either Harris Cyclery or Gaerlan's. They're square taper with a 110 BCD though, if that matters to you.

Thanks, Rhenning and delwong! Roger, I'm still not quite sure I'm measuring correctly, but the fact that you're a hair taller than I and that the 170's are the longest crank indicated for your size, tells us something. Peter White goes for longer crank arms, which I consider to be a more conservative approach.

Cyclistjohn, I'm interested in what Burrows says! I don't know much about him other than that he designed the Freight Eight, which looks to me like a wonderful machine. Does he suggest a way of determining appropriate crank length?

I would like to suggest a simplistic formula for determining crank arm length, for purposes of discussion only. This is based on a little research on the internet, in which I learned the following:

1. Bulletproof makes crank arms ranging from 140 to 165 mm.
2. Most manufacturers make them in the 165 - 175 mm range
3. Some manufacturers make them as large as 180.
4. LLBean sells jeans with inseam sizes 29, 30, 32, 34, and 36.

So if we stipulate that the largest crank arm size made (180 mm) is appropriate for someone wearing the largest pants size (36"), then you can estimate your appropriate crank arm length (in mm) simply by multiplying your inseam (in inches) by 5:
inseam 28" = crank arm 140 mm
inseam 29" = crank arm 145 mm
inseam 30" = crank arm 150 mm
inseam 31" = crank arm 155 mm
inseam 32" = crank arm 160 mm
inseam 33" = crank arm 165 mm
inseam 34" = crank arm 170 mm
inseam 35" = crank arm 175 mm
inseam 36" = crank arm 180 mm

I like the way this correlates the available crank arm sizes to the available pants sizes. If this is any indication, then it would seem that most of us use disproportionately long crank arms.

The thing that intrigues me, and the reason I chose to make this a new thread in the folder forum, is because this is where we find cyclists advocating unconventionally small wheels and other radical innovations. From my very limited testing, the effects of short or super-short crank arms are similar to the effects of small wheels. They are especially good for quick acceleration and spinning.

To enhance your research, you should also google "Mark Stonich." He's got a lot to say about crank lengths as well. Sometimes he posts here as mnHPV or something similar. Recumbent riders also have covered this topic pretty well as crank length makes a huge difference for those particular bikes.

To enhance your research, you should also google "Mark Stonich." He's got a lot to say about crank lengths as well. Sometimes he posts here as mnHPV or something similar. Recumbent riders also have covered this topic pretty well as crank length makes a huge difference for those particular bikes.

Thanks very much!

Stonich's web site has interesting stuff, including this page:
http://bikesmithdesign.com/Short_Cranks/short_cranks_faqs.html

which led me to this, very interesting:
http://www.velonews.com/tech/rev/crank.html

Makeinu, you can send Stonich your cranks and he'll lop 'em down for you (but it costs more than a new set of bulletproofs)!
http://bikesmithdesign.com/Short_Cranks/shorten.html

I'd guess any machine shop, perhaps even your lbs, should be able to do it as well.

Another BF thread on crank length, with a couple of reference URL's embedded:

http://www.bikeforums.net/showthread.php?t=167713

Another BF thread on crank length, with a couple of reference URL's embedded:

http://www.bikeforums.net/showthread.php?t=167713

John, thanks for that! This post, from that thread, sums up my problem pretty well:

I've had 170mm to 180mm and all I can say is that this whole issue is over-rated.

It's like saying "I've tried size 14 shoes, and I've tried size 15 shoes, and they fit exactly the same." Well, of course they do, if they're both too big!

Now that I have 152's on my Mini, I am noticing a real difference. The difference is so striking that I am seriously tempted to chop the cranks on my other bikes. Remember, the cranks on my Strida (170's) are compromised (read: junk) because the factory installed the L pedals in the R side and vice versa. So should I get new cranks, or just shorten them? Or, if I decide to buy a set of those Bulletproof BMX cranks, which size should I get? This leads to the question, HOW short is TOO short? Zinns (article cited in my last post) has experimented with cranks ranging from 150 to 180. And ... ? He writes:


Much to our surprise, every rider we tested performed superbly with the 150s! With one exception, all of us had our highest power outputs at a given heart rate with the 150s in the low power, early part of the test. The exception was that my best test was on 180mm cranks, the length I use all of the time on all of my bikes.

So, I would ask, what about 140's? 130's? 120's? and so on? A good experimental protocol would be to keep trying smaller cranks until one reaches a point at which disadvantages become evident; clearly with 150's that point had not been reached.

Maybe, as Alltheway said, the issue is overrated. But just because all cranks tested perform well enough, it does not necessarily follow that crank arm length doesn't matter. We know that all wheel sizes between 12" and 36" perform well enough, and all frame sizes perform well enough as long as the seat and handlebar can be set at acceptable heights, and so on. But what's optimal? I would like to hear from anyone who's actually tried super-short cranks; and I would especially like to hear about anyone who has found a crank arm length that is clearly too short.

I'd like to try out some supershort cranks myself. Anyone recommend a good source?


I use a set of 145mm cranks on a Speedwell 406mm wheel bike which is similar to a R20 but smaller. It felt weird to start with but once I got used to it, 50+ kmh is not unusual.

rhm, In my mind, this power test kinda misses the whole point of using shorter cranks.

"Much to our surprise, every rider we tested performed superbly with the 150s! With one exception, all of us had our highest power outputs at a given heart rate with the 150s in the low power, early part of the test. The exception was that my best test was on 180mm cranks, the length I use all of the time on all of my bikes."

Unless I am reading something wrong in that velo article, all the tests were performed at a constant 90 rpms. From listening to folks who have tried going the shorter crank route, the advantage they found was the ability to spin at higher rpm and thus use a lower gear. Some have said their spinning ability was enhanced enough to more than offset the speed difference brought on by dropping a gear. Hence, even though you are pedaling in a lower gear you end up going faster because of higher cadence. I saw no mention of testing enhanced spinning ability or comments from the test riders as to whether short was easier to spin than long. Seems kinda germane to the problem, if you ask me.

I've been threatening to get some short cranks to try for a while now. I haven't yet, well ....because I'm ....uh.... cheap ;) Now that I see these relatively inexpensive "Bulletproof" cranks that come in so many lengths. I'll probably finally bite the bullet and get it done. Thanks for the link to those.

Rik

Hi,

I use a 172.5 Shimano Dura ace crank set on a new 54cm cannondale sys 6, I used to have them in a optimo 56cm. I feel great on my new bike however I can hit the wheel with the tip of my shoes if I have them perpendicular to the hub. usually I hit the wheel on trafic lights, no problems while riding yet. My wuestion is should i change the crank to a shorter one and then raise the seat post? I can move the cleats anymore. Im just afraid that if one day I hit that wheel while flying I'll be landing in the floor.,

....I feel great on my new bike however I can hit the wheel with the tip of my shoes if I have them perpendicular to the hub. usually I hit the wheel on trafic lights, no problems while riding yet. My wuestion is should i change the crank to a shorter one and then raise the seat post? I can move the cleats anymore. Im just afraid that if one day I hit that wheel while flying I'll be landing in the floor.,

Hello Pieralberto,

I find that very interesting, as in another thread on wheel size, I mentioned that I'd recently seen a TV "Bad driving" type documentary showing a clip of a woman on a big wheeled bike catch her foot in the front wheel riding away from traffic lights, & fall off!

I finally managed to find a European supplier of cranks that aren't a cardiac inducing price, & have ordered a set. When they arrive & I've fitted & tried them, I'll report back, as I want to try them on 2 bikes. I'm interested in a couple of "side effects" of shorter cranks.

I suspect the seat post will have to be raised to compensate for the reduction in crank length.

Did you mean to write "can't" move the cleats?

I finally managed to find a European supplier of cranks that aren't a cardiac inducing price, & have ordered a set.

Would you mind passing on the info as to where you found the cranks?

Would you mind passing on the info as to where you found the cranks?

Certainly: I was going to wait until I received the goods, but I'm fairly confident the firm is ok.

http://www.dutchbikes.nl/index.html

about half way down the page.

Their description is for a "crack" set, but I hope they're really sending me cranks ;-)

It looks like they have some useful bits & pieces, especially small wheel stuff, since they specialise in recumbents. Hopefully if my transaction goes well, I'll buy more from them.

HTH.

sorry can't move them anymore:eek:

Thanks, cyclistjohn. Let us know how it works out. I'll be interested in ordering those in February or so, so would love to hear some feedback before I do.

Edited to add:
You inspired me to do some more searching. And I also managed to find a site selling 155mm triple ring cranks (of course they're substantially more expensive) in Germany if anyone is interested. About have way down this page.
http://www.hpvelotechnik.com/shopping/preisliste11_e.html (http://www.hpvelotechnik.com/shopping/preisliste11_d.html)

Thanks, cyclistjohn. Let us know how it works out. I'll be interested in ordering those in February or so, so would love to hear some feedback before I do.



They have been fine thanks over about 1000 kilometers. As they change the "gearing", I have noticed I drop down a gear more often. Interestingly I haven't felt a huge difference going from those on one bike to 175 mm. on another. No knee problems. I think I'll get another pair for my recumbent, but I'll need a 110 BCD, so will need to find another supplier.

Did you get a set yourself?

A data point:

I have a 36" inseam but rode 170 mm cranks for years because they were what came with the bike. Starting with a new bike I had 175 mm cranks mounted. I go back and forth between these two bikes and can't feel the difference. No issues of any sort. I've never tried anything shorter, but I suspect that I wouldn't be able to tell the difference down to, say, 165 mm.

I think I fall into the this issue is over rated camp.

Speedo

The issue is overrated. I'm 5'3, with proportionally shorter legs, and I used 170mm cranks for years (including a 10-year period in which I was car free) with absolutely no complaints. My Bike Friday came with 165mm cranks, and I can't say that I've really noticed any difference in pedaling. Which is kind of interesting, since the bike being custom made means that I have noticed improvements in *all kinds* of other areas.

So I fall into the "overrated" camp as well.

(Alternatively, most people may be using cranks that are too short; it doesn't intuitively make sense that someone 6'2 would be as happy with 170mm cranks I used to use as I was - but 185mm cranks would likely hit the ground. So perhaps 170mm was settled upon as the longest length that wouldn't cause ground strike issues for most people?)

I do not believe smaller than 170 mm. cranks are "overrated".

Some people use them because longer cranks give them knee pain. If a rider has no knee pain, & tries shorter cranks, with no great difference, then they may consider such "overrated".

Recumbent riders in particular seem to find shorter cranks better.

I don't have the URL's to hand, but can probably find them if requested, which highlight measured rider power output improvement with shorter cranks.

I did a little testing on my road bike. It's not conclusive, but it's worth sharing.

My bike came with 172.5mm crank arms and I bought a 165mm crankset off of Ebay to test. I tried to get as big of a difference as I could, so that I might be able to actually feel it.

I raised the seat to compensate for the difference in pedal height at extension.

Ultimately, I did end up spinning at a higher RPM. The shorter cranks encourage you to keep it in a lower gear and keep the revs up. The only think I can really compare it to is a car with a small, high RPM engine. The only way to keep it happy is to be revving the snot out of it.

It did seem to hurt me going up small hills and rises. Places where I needed to just apply a little more pedal force previously required either more pedal force or a downshift. This can be an issue because on a standard road casssette, you only have so many gears. I didn't want to have to be bouncing between chainrings.

I did one good climbing day with the short cranks. My overall feeling was that they took a bit of torque away from me and made the climb a little tougher. What they did that was positive was made climbing out of the saddle easier. I was rocking the bike much less side-to-side and it tracked very straight out of the saddle (about a 10% climb).

My Air Friday has 175mm cranks and a 62/52 chainring combo. I'm thinking about putting the 165 cranks on it with the 53/39 chainrings. I'm always by myself on the folder, so I don't need the big buzz-saw gear. Having the ability to drop to a 39 would be nice on some of the serious climbs I do (on the order of 15%). Using Sheldon Brown's gear calculator, that gives me a much lower overall gearing, but the shorter cranks should allow for a higher spin-out, should I get in a group.

Incidently, I was professionally fit to my new (to me) road bike. The fitter told me that 172's were the right crank length for me. She would have only put me on 165's on a track bike. My inseam is 31", so I don't think that inseam/crank length chart is really too accurate. There's more going on that just that.

Has anyone experimented with different crank arm lengths?

170 mm seems to be the standard, but I have a collection of cranks I'm not using, so I've been trying out some different lengths. For the last week I've been using 175's, and hated them. Good leverage for going up hills slowly, terrible for anything else. So for comparison now I've switched to the shortest ones I had, the 152mm (6") crank that came on my Kent magnesium folder. As you'd expect, not much leverage; but great for spinning! I may actually stick with this one....

Isn't crank arm lenght kind of a moot point on a folder or any small-wheeled bike? I have 175mm crank arms (16" wheels) and I drag pedal constantly unless I make a very conscious effort to pay attention to which pedal is up at any given turn. I'd say since most of us aren't riding these on high performance rides, go with a shorter crank arm just so you don't constantly scrape. I realize there are die-hards that ride folders exclusively, but so far my impression (and my own practice) is that most stick with their regular road bikes for performance rides and ride folders for convenience and transportation purposes.

Isn't crank arm lenght kind of a moot point on a folder or any small-wheeled bike?

It depends on the design. My BF has a reasonable bottom bracket drop that mean the 175 cranks are no big deal. It's going to depend on frame design.

[QUOTE=Fat Boy;6639809]I did a little testing on my road bike. It's not conclusive, but it's worth sharing.

My bike came with 172.5mm crank arms and I bought a 165mm crankset off of Ebay to test. I tried to get as big of a difference as I could, so that I might be able to actually feel it.



So if you had your choice would you pick the 172.5mm?How did you measure you inseam?

I am kind of wondering the same thing' my first 2 bikes had 170mm on them which i rode for 6 years.I brought a new bike the same size and it came with 172.5.I think what ever size they have laying around when they build these bike is what they put on.I thought this just is not right I need 170mm.They just seem to long.I wonder what the 170mm would feel like on this bike .Its like a big mind game every time i went out for a ride. Its dura ace so its a very costly switch for 2.5mm.Well after about 900 miles later they do feel pretty good ..Not sure if the body had to adjust to them and the bike in general.Or if its all in my head.Do I want to try the 170mm yea it sure cross's the mind. Is it worth the money for 2.5mm probably not.