rhm

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....

james_swift

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.

rhenning

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

rhm

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?

delwong

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.

cyclistjohn

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.

delwong

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

rhenning

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

makeinu

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

spambait11

BulletProof cranks sold at either Harris Cyclery or Gaerlan's. They're square taper with a 110 BCD though, if that matters to you.

rhm

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.

spambait11

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.

rhm

Thanks very much!

Stonich's web site has interesting stuff, including this page:
https://bikesmithdesign.com/Short_Cra...anks_faqs.html

which led me to this, very interesting:
https://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)!
https://bikesmithdesign.com/Short_Cranks/shorten.html

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

cyclistjohn

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

https://www.bikeforums.net/road-cycling/167713-crank-length-climbing.html

rhm

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

stevegor

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.

oldguy52

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

Pieralberto

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.,

cyclistjohn

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?

fmattheus

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

cyclistjohn

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

https://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.

Pieralberto

sorry can't move them anymore

fmattheus

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.
https://www.hpvelotechnik.com/shopping/preisliste11_e.html

cyclistjohn

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?

Speedo

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