Pepelapu07

goodevenig all,looking for right crank arm fit.im 5'7 ,30 inseam.have a 49cm roadbike with 50tt.whats best fit for my height and 49cm bike?170mm or 172.5mm? thanks

Grand Bois

170.

randyjawa 

+1

prathmann

Probably 165mm or less but it might be harder to find. Odd that crank arm lengths are clustered in such a narrow range. My bikes range from 165mm to 175mm and they all feel fine to me. Would hardly notice the difference at all unless I really concentrate on it.

T-Mar

For average proportioned person with that inseam, I would be starting with a 167.5mm or 170mm crankset. Fine tuning would depend on you thigh measurement, foot length and the frame's seat tube angle.

SteelCharlie

The difference between 165mm and 175mm about 0.4" and if you think that you can feel that difference you are star material and should be looking forward to the TDF. The 175's give you a minuscule more leverage and that is a good thing. I'm the same general size as you are and I've been using 175's on everything for a few decades and I tried everything from 165 and up on the same advice as you're getting here. I don't and never did spin @120+ r's all day long and you prolly don't either. Watch the TDF'ers - neither do they.

More importantly if you're 5'7, 30 inseam and have a 49cm roadbike you should be looking for a bike that fits before you worry about the cranks. A traditional frame configuration of 53-54cm would be far more likely to provide you with a quality experience. I'm talking real world go for a ride have a good time fast as you can and don't hurt yourself kinda experience.

prolly not JMO but YMMV and it's your back and neck

besta luck

mtnbke

No.

Crank length should be proportional to frame size, but really it's a function of your cycling inseam. I'm 6'7" and ride 68-69cm bikes with 205mm, 200mm, 195mm and 185mm cranks.

Too long can hurt your knees. Too short can help you spin, and there are all kinds of data and anecdotal evidence showing cyclists are more efficient t with shorter cranks

Essentially, 175mm or 170mm cranks really aren't ideal for most cyclists. Component manufacturers don't want to make different sizes, but cranks should come in 2.5mm increments between 155mm-230mm. Almost everyone rides on the wrong size cranks.

rhm

Crank arm length doesn't matter much. Regardless of leg length &c we can all walk up the same staircase and it feels normal to each of us.

While it is true that longer cranks give more leverage, more leverage is not needed in normal cycling.

When choosing between two cranks that are otherwise equal, choose the shorter one.

Lazyass

I'm no star material for the TDF but I have bikes with 170, 172.5 and 175 cranks. I feel a difference between all three, especially the 175's. But I do ride almost every single day and am very sensitive to small changes in cranks and everything else. Mileage has more to do with it than how fast you are. If someone can't feel any difference they probably don't ride all that much.

TimmyT 

+1 This is the correct answer. Most of the "fit" associated with inseam is fixed in the seat post.

-holiday76

No.




Yes.

SteelCharlie

Unless those bicycles are otherwise absolutely identical in every regard I would suspect that you are feeling the many differences that accumulate to make a bike "feel" as it does and not the cranks alone (if any).

I ride three different, very different, bikes currently - Caylor (175), Masi (175), Colnago (172.5). The Colnago had 170's and the thing feels just like it did with them. The Caylor has been with me for a few decades and has had everything from 165 to the now 175. Nothing else had changed on the bike since 1984. Still feels samo samo. The cranks are close enough to same as can be so why don't the bikes all feel the same?

Or I suppose I should just admire and envy your sensitivity - but I would wonder why the one that feels the "best" is not pervasive?

It's been my experience that proper bike fit obviates crank length since that is accommodated by the adjusto components.

Again - JMO ride what you like

alathIN

I got a high level bike fit on one of those "robo bikes" where they can change every fit dimension on the fly.
Going from 172.5mm cranks to 165mm increased my RPM at the same perceived exertion and "free" 4-5 watts.
I'm 6'1", and bikes my size always come with 175 or 172.5, so yes I realize this is quite a bit shorter than conventional wisdom.
Next outdoor ride after those changes (admittedly all the fit changes too) I set PB's for 40m TT and normalized power.
This is a TT/Tri bike, so maybe this is not as critical of an issue on other bikes.

After this experience I did put 165mm on my gravel/rando/touring bike. I don't have a power meter on that bike, so no objective measures, but I do have the sense of a decreased "dead spot" at the top and bottom of the pedal stroke and a more effecient/smoother motion overall.

I am not aware of any downside to decreasing crank length. Based on my n = 1 anecdotal experience, I'd try 165s. It's hard to imagine that 165s would be perfect for me at 6'1" and too short for 5'7". However, just to show how random and individual this all is, my inseam is only 1" longer than yours.

ksryder

Hot take: People are different.

Just because *you* don't notice a difference between crank arm sizes doesn't mean that is universally true for everyone. I had some pain issues that were eventually alleviated, in part, by changing crank arm length. (There's a lot more to it than just that but that's the short version.)

So for *me*, I can definitely tell a difference in crank arm length because of my unique physiological circumstances.

But I also don't tell other people, who say they don't notice a difference, that they are wrong.

See how easy it is?

frisky99

I just picked up a 87 trek 1200 size 21 and was surprised it had 65's on it . I was expecting 70's.

Eric S.

Maybe it has something to do with longer cranks, but I can feel a difference between a set of 177.5mm I have on one bike and the 180mm arms I have on all the others.

Princess and the pea kind of thing, I guess.

SteelCharlie

I didn't say you or anyone else were wrong when I commented on your statements. I merely suggested that there is more to "feel" than crank arm length. To ascribe the difference in the feel of different bicycles to a single component that is subject to mitigation by nearly the entire rest of the machine is absurd.

A gent I rode with many years ago had one leg shorter and he rode different crank lengths and a spacer under one cleat. Of course he wasn't searching for the last milliwatt but then so few of us are, eh?

JMO of course - - - ride what makes you happy

Charlie

The Golden Boy 

I'll agree... I'm 5'8" wearing 30" trousers... I feel positively smunched on a bike smaller than 21" (52-54). And 22 (56) is just out of my comfort range.

I know you weren't asking about fit- but... yeah.

I have 170s on all my "road" or "sport" or "touring" bikes. The two ATB style bikes I have are equipped with 175. I think that may be as for needing leverage and having a higher bottom bracket.

rhm

Yup.

I am not aware of any downside to decreasing crank length either; at least from the point of view of speed, efficiency, comfort, etc.

I believe there would be benefits to designing bikes for shorter cranks than 165; but that would be a major change, requiring lower bottom brackets etc, and I don't see the industry going there. Why should they? We all seem to do okay with the cranks we have, which are effectively all the same size anyway. But when offered the choice, I still go for the shortest cranks available.

Spaghetti Legs 

Thread summary: some think it makes a difference, some don't.

I think the takeaway for the OP is don't stress over that 2.5 mm (1/10 inch!). I am in the "no difference" camp and would choose a shorter crank when I'm concerned about pedal strike, like for a crit bike or mountain bike.

corrado33

I vote 165s for you, but you'll likely end up with 170s and be fine.

I typically ride 170s and 172.5s and I'm a few inches taller than you. No, I cannot tell the difference.

As some said, longer cranks give you more leverage (arguable whether or not that means anything), but shorter cranks are nicer on your knees.

tbo

49 cm frame? That's fairly small. Larger cranks (and big feet) may end up having clearance issues with front tire. That's especially problematic if your feet are mechanically attached to the pedals via clips, cleats, etc.

Pepelapu07

Thanks for info.The 49cm give me about inch clearance betweem cajones,and top tube.Is it not the right fit for someone like myself?

Pepelapu07

Thanks all.Much appreciated insightfull information

old's'cool

Be that as it may, for actual riding comfort, the fit in the riding position is more important. Unless you mean 1 inch clearance is when you're riding