Mariner Fan

175 feels best for me.

6'2" with a 36" inseam.

ironwood

I'm about 5'8" in the morning. My bikes have 170 or171mm crankarms, But I might put on 165s on a bike that has a loww BB after a 650B conversion. If I could find some 167.5 cranks I'd use them, but TA is the only maker of that size I know of, and they are tres cher. Maybe if the Euro drops or someone like VO would produce 167.5s I'd get some.

jimmuller 

170 on most bikes
165 (because it was available) on the Bianchi (which has a high BB, so don't ask why it works so well but it does)
171 (dug up from the parts bin, and yes, that's what it was) Sugino Maxy Compe recently installed on the Bertin
I can't feel much difference between them.

Height about 5'9.5"
In-seam (I dunno' but normally proportioned, I think)
(There are other pants-related length measurements I don't know either.)

gaucho777 

I found this list interesting. In my experience, 170s seem to be the most common crank size in the real world, but apparently not in the pro peleton:

Jacques Anquetil 175mm
Lance Armstrong 175mm
Magnus Backstedt 177.5mm
Chris Boardman 170mm
Santiago Botero 172.5mm
Angel Casero 175mm
Mario Cipollini 172.5mm
Fausto Coppi 171mm
Malcolm Elliott 172.5mm
Tyler Hamilton 172.5mm
Bernard Hinault 172.5mm
Miguel Indurian 180mm (190mm for second Hour record!)
Laurent Jalabert 172.5mm
Greg Lemond 175mm,
Brad McGee 175mm
Robbie McEwen 175mm
Eddy Merckx 175mm
David Millar 175mm (180mm in TT)
Francesco Moser 175mm
Marty Northstein 167.5mm in Keirin (170mm in kilo)
Graham Obree 175mm
Marco Pantani 170mm (180mm in mountains)
David Rebellin 172.5mm
Roger Riviere 175mm
Jean Robic 170mm
Tony Rominger 172.5mm (175mm for Hour record)
Oscar Sevilla 175mm
Jan Ullrich 177.5mm
Rik Verbrugghe 175mm
Erik Zabel 172.5mm
Alex Zulle 175mm (180mm in mountains)
Alberto Contador 172.5
Fabien Cancellara 177.5
Tom Boonen 177.5mm
Allan Davis 172.5mm
Gord Fraser 172.5mm
Oscar Freire 172.5mm
Thor Hushovd 175mm
Giovanni Lombardi 172.5mm
Alessandro Petacchi 175mm
Fred Rodriguez 175mm
Erik Zabel 172.5mm

Source: LINK

cpsqlrwn

Even though this poll doesn't bear this out, I think 172.5 may have supplanted 170 as the most common, whether it be the everyday rider or the pro.

Scooper

Framebuilder Bill Boston is the author of Accufit fitting software and uses thigh length as the major measurement to determine recommended crank arm length.

Discussion HERE.

Bill Kapaun

I use 165's (cadence about 85 RPM), but it's because of a bad knee that doesn't have full range of motion.
170's (cadence about 82 RPM) and I'm having some degree of knee pain.
175's (cadence about 60 RPM) and I WON'T ride. It causes severe knee pain. My foot comes off the pedal @ 62-3 RPM at the 12 O'clock position.,
Tried 160's but my cadence actually decreased to 80ish. Proves to me, at least, you can go too short.

I used to be a "scant" 6-1, but more like 5-11 now. (Getting old)
Never measured my "bike inseam", but I've typically worn 31-30 inseam pants.

Italuminium

172.5, 5,11 32. I rode some 170 and 175 too, but honestly, neverbothered too check if it made any difference.

mikemowbz

Looking at gaucho777's list, above, and some of the other comments, it occurs to me that terrain is really the difference-maker - I miss my 175s when I've got some topographical variation (read: hills) in front of me on my 170-equipped Marinoni and my mashing feels somehow off, whereas I'm actually quite happy doing rounds on the smooth and largely level bike/rollerblade loop in the park...which makes perfect sense, of course. Still, this makes me all the more keen to try some 177.5 or 180s when I get back to Vancouver, where the terrain is unquestionably hilly

JohnDThompson 

165mm on my fixed gear bikes.
170mm on my other bikes.

hairnet

6'5'' - 37.5" fromunder to floor

180mm cranks on my regular road bike and 175mm on my fast bike. There was a very noticeable difference when I first got my 180 cranks and still 175s are the most comfortable to spin even 100+ rpm. I have ridden 165, 170, and 172.5mm cranks. I have a 170mm DA cranks when I get a "go fast" fixed gear again

paulkal

I am using 170, 175.5 and 180 mm cranks. My height is 1.95m, inseam I don't know.
I don't notice any difference between the cranklengts.

gomango

6'1 or so, 34" or so, 172.5mm

...although I have 175mms on a bicycle or two.

My kids assert I am shrinking as they grow taller.

Nowadays I spin happily away, but I used to mash when I had enough cartilage in my left knee.

Three knee surgeries will do that and my right knee is feeling the onset of RA.

Yep, I am falling apart.

Loved playing hockey and skating in general when I was younger, but it appears it isn't doing me any favors as I age.

A friend that owns a local racing shop has asked me to do a refit for years and has a very similar line of thinking as Repechage on this topic.

jimmuller 

Re crank length vs. terrain, switching from 170 to 175 cranks is equivalent to shifting from a 24T cog to a 24.7T cog. (There is one on ebay right now. ) Which is to say it may matter for one's ergonomics but the effect on gear ratio is negligible.

H.S.Clydesdale

Other = 200mm

Actually, I currently have 170mm because they came with the bike, but am saving up for some of these:

https://www.bigandtallbike.com/Zinn-C...oad_p_160.html

The only problem is, they would cost more than my entire bike setup, and because I dont have a custom zinn frame, I am worried I'll be scraping the ground with my pedals, given that my BB clearance is only 270mm.

height = 6'7"
inseam = 37"

noglider 

Which is one way of showing how mysterious this whole topic is.

I got to check "other" in the poll, because my McLean has 167.5mm cranks. I have them because that's what the shop had on hand at the time and I shrugged and said why not. I don't notice the difference between them and other cranks, because I can't do an apples to apples comparison: I don't have two identical bikes except for crank lengths.

I'm amazed that 5mm is noticeable, but enough people can feel it that I believe it. In fact, I think one major reason I didn't like my MTB (which I no longer have) is that the cranks were probably 175. To jimmuller's point, yes, it makes a tiny difference in leverage, but as gomango points out, the range of motion could be the critical factor. But this is extremely hard to prove.

rhm's theory is that we're all riding cranks that are too long, if I understand him right. He has even shortened cranks for himself. I'm willing to believe him but don't have the time or money to test it.

I'm about 69.5 inches tall (176 cm). I have short legs. My Levi's jeans say 30" inseam, and I think my PBH is about 33 inches.

Most of my bikes have 170 mm cranks, except, of course, for my 3-speeds.

mikemowbz

Indeed. When my great wish is to affect gear ratio, well, that's what messing with the gearing is for .

Again, this may be all in my head, but, for whatever reason, I do feel like - on a bike with otherwise similar dimensions/setup - the longer crank is preferable on more mixed (or practically vertical) terrain. Ergonomics, quite likely. I don't really know. I do ride quite differently under the respective conditions usually presented by hilly/mountainous Vancouver and relatively level/gently sloping Montreal. That difference is more or less effectively captured by the mashing/spinning dichotomy.

I did find interesting the mentions in gaucho777's list of pros using 180mm (rather than 170 or 175) for 'mountains'. Do they do it for the infinitesimal impact on gear ratio, or for some other reason (i.e. ergonomics)? Or is it about as empirically useful as hockey players growing beards in the playoffs? I really don't know about any of this stuff technically, so I'd be interested in any further insight...

jimmuller 

Here is another (perhaps obvious) point about crank length. You set your saddle height to accommodate the bottom of the pedal stroke. A 5mm shorter crank means the top of the stroke is 10mm lower, not 5mm, w.r.t. the saddle height. And this means your knee and hip joint operate on a scaled-down range of motion. The nominal maximum torque position, i.e. a horizontal crank, is 5mm lower w.r.t. the saddle, so the hip to back angle at the pelvis is slightly wider and the knee is slightly straighter. These ergonomic factors may indeed be noticeable, and would perhaps allow a greater saddle to bar drop.

From this persepctive it is easy to see why one might wish to scale crank length to thigh length. For a given thigh rotation angle at the pelvis, the total range of motion of the knee position from top to bottom depends on the thigh length, because that's the arc length which the knee swings through. So one might wish to figure the optimal knee and thigh angles, then scale the crank accordingly. This is not to say that a greater or lesser angle is better or worse, but some people seem to have fewer joint problems when the range or motion is less.

repechage

Most of the above makes sense, but If one changes crank lengths one assumes the saddle height is changes also. Moving from 175's to 170's would suggest a lowering of the saddle. The top of the pedal stroke is also now 5 mm less assuming one lowered the saddle 5 mm too. I am not clear how you arrived at a 10 mm lower dimension for the top of the stroke as we are dealing with a radial measure.

Italuminium

Interesting points. When a friend of mine applied for chiropracty school, we were given a tour of the facilities. One of the "attractions" was a full check-up by one of the nearly graduated
students, under te guidance of am old hand. The teacher immediately spotted a leg lenght difference in me, leading to lower back stiffness. Now and them, when i ride to high a gear, my right leg gives out sooner then my left (the shorty). Anyone mix and match cranks to compensate for leg lenght difference?

rhm

Saddle height and crank arm length are related, but not to the top of the pedal stroke. Since your leg length is a constant, the seat should be set relative to the bottom of the pedal stroke. So if you reduce your crank arm length by 5 mm, the bottom of your pedal stroke goes up 5 mm, so your seat has to go up 5 mm. Assuming the BB height has remained the same, the ground will have got 5 mm farther away from your center of gravity; so to retain the same geometry you will also need to raise your handlebar 5 mm.

I know someone who does, but it's not my story to tell.

The Drysdale bike I bought a few months ago came to me with a 175 mm left crank arm, and a 165 mm. I don't know why that was, of course.

jimmuller 

As rhm said, a 5mm shorter crank means the pedal is 5mm higher at the bottom of the stroke (and 5mm lower at the top). People usually set saddle hieght to create a preferred (i.e. maximum) leg extension, be it nearly straight or whatever is desired, at the bottom of the stoke. Perhaps some people do it differently. But for most people if the pedal is higher by 5mm so will be the saddle in order to keep the preferred leg extension the same. Of course this means the distance between pedal and sadle at the top is 10mm greater, 5mm because the saddle went up and 5mm because the pedal went down. Or to put it simply, the pedal circle radius is 5mm less and the diameter is 10mm less.

cyclotoine

I have, don't do it. I would not assume your lower back stiffness it related. Before you anything have someone film you in a trainer and your bike from straight on so you can pause it at the bottom of your pedal stroke or at least have someone observe you in a trainer. If one foot is obviously pointing more than the other than you have a functional leg length discrepancy and not necessarily an actual one. You may be able to correct this with strengthening exercises and chiropractic. You may also try to turn the nose of your saddle slightly to the side which is behaving shorter. This will drop your pelvis on that side and effectively lengthen that leg.

Lastly, always seek to treat the cause and not the symptom. That is to say try to work on your body before you start altering your bike to compensate for a difference. It may be in the end that altering your bike is best but try the other route first. I tried using a 5mm longer crank for my longer leg and it caused me all kinds of pain. It's more complex than you think. Your pelvis may be tiled so the longer leg side rides higher and when you are in the saddle your longer leg may behave as though it is shorter (i.e. more reaching with the toe and blown calve muscles on that side before the other). It's complicated. I would recommend a cleat shim rather than different crank lengths so the circle is the same on both sides, but the center of it is raised. That way you have the same amount of flexion in both hips and knees.

cyclotoine

The fact is that as one's joint position changes, the engagement of the muscles change. Push on an object with your leg extended just sitting and tell me which muscles feels more engaged? Now push on object with your knees close to your chest and tell me which are using most. The fact is that as you close the hip to torso angle you increase power (the power meter on the fitting machine at the shop I used to work at proves this on every cyclist). Do you ever wonder why the taller cyclist have more drop? I don't. It is because their cranks are not really that much longer than everyone elses' and as such they need more drop to close the hip angle at the top of the stroke, i.e. to create more power. Our fitting machine has adjustable crank length. Out of curiosity we changed the lengths around and the longer we made them the more power I was putting out. Why? Because as my crank length increases my top of saddle to bottom of pedal stroke was adjusted accordingly to be the same measure and as the crank got longer the distance from the top of my saddle to the top of the pedal stroke got smaller. The hip angle closed more and I made more power. The fact is that you engage more of you upper legs as you close that hip angle and your quads are big and powerful so it stands to reason that you would find that you climb faster when you use your quads to hammer up those climbs.

cpsqlrwn

+1