hobkirk

Is there much difference in feel or efficiency based on crank length?

I imagine it does matter quite a bit since it seems almost every crank is offered in 170m 172.5, and 175. But I come here to learn (and be entertained).

FWIW, I am 6'2" and ride about 150 miles per week. My current cranks are 175.

Gharp23

I am curious as well. I am 5'9 and ride a 20' frame with 175 cranks. Would it benefit me to downsize?

ddeadserious

I may be wrong, but I'm fairly confident it's mostly preference. Shorter cranks are going to be better for spinning, but you won't have as much leverage since the arms aren't as long. Longer cranks are going to have more leverage and thus easier to get going but maybe a bit more awkward to be spinning since there will be a larger range of motion. On some bikes(like fixed gears, or bikes with particularly low bottom brackets), it's more crucial to select the proper crank length to avoid pedal strike on turns, but I believe that's not as much of an issue on modern road bikes.

datlas 

Ride more.

Worry less.

prathmann

My road bike has 175mm, my touring and folder bikes have 170mm, and my tandem has 165mm cranks. I constantly switch between 170mm and 175mm and never notice the difference. The shorter cranks on the tandem are slightly noticeable, but I just tend to spin a bit faster in a lower gear to compensate. Can't really say that any length is better or worse than another.

carpediemracing 

Personal preference.

If you're sensitive to 5mm of saddle height change (just change your saddle height arbitrarily up or down by 5mm and go out for a ride and see if it feels weird) then you'll probably notice 5mm of crank length difference (total of 10mm difference in the diameter of the circle the pedal makes).

Since my personal preference is for longer cranks, I'll explain a bit about how I ride. If you're similar then you may like the longer cranks. If not then not.

I tend to push when under pressure, I rely on short bursts of power (while drafting or in races), and I don't do well on long climbs. Longer cranks work for me - with a 29" inseam (and saddle to BB height of about 67 cm, 175mm crank, Look Keo pedals) I use 175mm cranks. I tried to go back to 170s in 2008, unsuccessfully. I'm still thinking about it now (will build up my backup bike with 170s).

I find that the longer cranks work really well on power hills, meaning shorter, out of saddle hills that you can roll over using higher power. For me that means little roller hills about 20-60 seconds long, where normally I'd use a 39x15 or 39x17 and instead I'm rolling a 53x15 or similar.

Longer cranks do NOT help me on sustained climbs, meaning more than a minute or two. In fact I think they hurt me once I'm back to a sustainable effort (i.e. not anaerobic, so efforts of more than a few minutes).

I don't time trial but I can get either crank length up to speed okay, seated, 35-37 mph.

Interestingly enough I sprint faster on the 175s than the 170s. I lost enough leg speed that even after a year on the 170s I couldn't sprint as fast.

When I was younger I was fastest on shorter cranks but I spun more and weighed much less. As I got slower and heavier and more powerful I've gone to longer cranks. 167.5 -> 170 -> 175. I spent about 10 years on each size, +/- 2 years. My weight went from 110 lbs to about 140 lbs to about 180 lbs (no height change). I'm hoping to get back to the middle weight range and then be able to use the 170s effectively, i.e. gain 2-4 mph in top speed (the 167.5s had me going 4-6 mph faster than I do now).

I have two good friends, former leadout teammates, good sprinters on their own, who are about 6'2" 6'3", both ride a 60 cm frame, both have about 35" inseams (they used to trade bikes on rides, they are that similar in fit). They both run 180s, and the one that's more in the bike industry is constantly talking about trying longer cranks (per Leonard Zinn). Both used to race. One does group rides still (last race was in 2001?) and the other has dabbled back in racing but really stopped in 1997. Both were using 180s back then and still use them now (albeit on newer/different bikes).

hobkirk

Thanks. About what I thought but I was hoping for someone with experience.

Really useless! I rode 1500 miles in the last two months - how many did you ride? And your signature includes "never underestimate the idiocy of BF." Look at the useful answers from the others.

Thanks! That's right on point. You reassure me that it's worth the experiment (I may have found a good deal on a 172.5 crank).

Wow! That's a pretty spectacular answer! My take-away is that shorter is probably fine for my purposes.

• I am not sensitive to saddle height (I've raised it 1 1/2" from where it was "fitted" and I don't notice much difference for 1/2" or so).
• I've lost 33# in the last 3 months (standing didn't do much good at 238#) but I still don't stand a lot. (205# now, 185# is my target which is 2.5#/inch, Joe Friel's [approx.] "standing doesn't work well if you weigh over 2.5#/inch" - PS - FYI, he says the best climbers usually weigh 2#/inch or less!

Altbark

I'm 5'7" and use 170's on my SS and my road bike. My Cannondale T1 has 172.5's. I do notice the difference. I can spin faster and climb better with the 170's. I had a chance to ride a bike with 175's and found the bike to be sluggish. It is important to remember that you are converting reciprocating motion into a spinning motion. Legs have a lot of mass that has to be moved through a full cycle of the crank. The longer the distance travelled - the longer it takes. I haven't had the opportunity to ride a bike with 165's in a long time but it would be interesting to see how much faster I could spin with them or whether the point of diminishing return would be reached. Al

As an aside, the seat on my T1 with the 172.5's is set slightly lower than what I have set on my other bikes and my thighs tend to come up farther towards a not so flat 58 year old tummy.

Scooper

Bill Boston, framebuilder and author of the fitting software "Accufit", uses the rider's thigh (femur) length to determine crank arm length.

THIS LINK on the Accufit website discusses the biomechanical physics.

Flatballer

It does make a difference, but you're on a good size. I originally had 175mm cranks, but I ended up trying some 172.5mm and I liked them. I prefer to spin rather than "push" as CDR puts it. I'm 6 feet, don't know my inseam off the top of my head.

My track bike has 167.5 cranks, but track bikes are different.

JohnDThompson 

20' frame?!



But seriously, if you're comfortable with the 175mm arms, there's no compelling need to change. Longer arms give (slightly) better leverage; shorter arms make it (slightly) easier to spin. For me, the only compelling reason to seek a specific arm length (165mm) was to improve cornering clearance on my fixed gear bikes.

carpediemracing 

It seems that site bases crank arm length on the assumption that the average crank length (170mm) fits an average male. It doesn't even question whether or not it's correct or not, it just assumes it is. Then it uses the same proportions to assign crank lengths to different size riders.

To me this doesn't make sense. Although I may disagree with a study's findings, at least do a study that examines the relationship between crank length, leg length, and power/efficiency, not just assume that what's out there is out there because it works. It's out there because it's what someone decided should be on a bike they were selling.

merlinextraligh

6'1" 34" cycling inseam. Most of my bikes are 172.5mm. Tandem has a 175mm crank. I really can't tell much difference, that I attribute to the crank length.

Scooper

Good point.

garciawork

I used 175's on my MTB, and 172.5's on my road bikes for years. Then I realized my cadence was insanely high all the time on the road, so I decided to try 175's, slowed my cadence to around 110, gave me more torque when out of the saddle, and felt better all around. According to most calculator's I should be on 172.5's but I can't STAND riding cranks that short anymore. Most don't seem to notice a difference, to me it is huge.

I would at least say it can't hurt to try a different size out and see if you notice a difference, you may prefer shorter cranks.

pallen

I have a 170 and a 175 and cant tell a difference. I have swapped the cranks between the two bikes and still cant tell a difference. I'm not really sure why they make them different lengths so close together. Maybe someone can tell the difference between a 170 and a 175, but can they tell the difference between a 170 and a 172.5? I seriously doubt it.

nhluhr

At 6'2", I think you're closer to being able to benefit from a 177.5 crank than from wanting to step down to a 172.5, but I don't know your leg length.

I'm 6'3" and ride 175s (because I haven't bothered to search for different lengths) but I consistently notice that I turn higher RPM than my ride partners at a given speed - perhaps that has something to do with the short-for-me crank length.

I'm at 1,544mi for the month so far and have always ridden 175s on my road bikes because that's the typical max length (higher end cranks often come in 177.5 or even 180 if you can find them).

Commodus

I think there are two, or maybe three major viewpoints in this debate. Those held by Lennard Zinn: https://zinncycles.com/Zinn/index.php.../custom-cranks and Peter White: https://www.peterwhitecycles.com/fitting.htm

Steve Hogg: https://www.stevehoggbikefitting.com/...gth-which-one/

And the ever-pragmatic Grant Peterson: https://www.rivbike.com/kb_results.asp?ID=54

Who is right? You got me, but it's an interesting subject and much has been written on it, if you're interested.