sactown

I am thinking about buying a new crank set for my bike. I am about 5'11" and 175. What length is would be appropriate for me. Would 172.5 be ok or would I need 175.

labrat_62

i am 6'2" and use a 172.5

crash13

I'm 6'2" and ride a 175mm. However, I test road a Look 595 the other day that had 172.5mm cranks. They "seemed" to spin up much quicker...This could've been other certain attributes of the 595...I might switch to 172.5mm. Doesn't seem like I need the extra 2.5mm. Well, at least not on my cranks!

Hop on Bike

https://www.nettally.com/palmk/crankset.html

https://www.cptips.com/crnklth.htm

https://www.sheldonbrown.com/cranks.html

cmyke

Why does everyone think your overall height has anything to do with sizing when it comes to a bike? It's INSEAM length! You know, because.. your LEGS turn the cranks.

I'm 5'9, and while many guys my height ride a 56cm frame, my ideal frame is a 53, because my inseam length is lower (my legs are more proportional to my torso). The same sizing method applies for crank size.

If you want a ridiculously long explanation, go here. It talks about determining your ideal crank arm length from your inseam.

kwheaton

cmyke -- your hyperlink to the long explanation doesn't work. Try again?

2WheelFury

Here I figured it out for all you non-Internet savvy types. . .

https://www.nettally.com/palmk/crankset.html

531Aussie

I only get on these threads now to debunk Palm's crazy "theory" in the hope that no-one will follow it.

A crank length of 21.6% of inseam is insane. That would have me on 193mm cranks! That is so crazy I can't even believe it keeps coming up. I'm 6ft with long legs (35.23"), I tried 180s for a year, which are 'only' 20% of my inside leg, and they were too long. I now mostly ride 175s and 172.5, and I have 177.5s on a bike that I'm epxerimenting with.

to the origianl poster, I figure 172.5s, 170s, or maybe 175s

Robert C Wells

I'm 6'.5"(not 6'5") tall with an inseam of 32.25". According to Palm's formula, I would need 175mm cranks. I'm currently riding 172.5mm cranks and my seat post is almost at it's max height. I've also noticed that my seat height compared to stem height is well over 1 in. difference, and from what I understand, that diff should only be about 1in. Now I'm fairly comfortable on the bike as is, but with my longer inseam and the fact that the seat post is at max height, then should I or should I not go to the 175mm crank?? This is advice only, I realize it's totally a subjective thing, but you seem to have some experience here.

531Aussie

nah, I haven't heard that recommendation about a 1" drop from saddle to bars -- it varies greatly. In fact, I'd say 1" is generally too little for a 'racing' setup. although there are no set rules.

Is that you pants inseam or your real inside leg? That sounds short for someone just over 6ft. Either way, you won't notice too much difference going up 2.5mm, and it's not worth spending the money.

Robert C Wells

Well, I just had my wife remeasure (I took the first one), and it's actually 33". So it would actually be a longer crank needed. I'm about to make a change regardless, and just trying to decide whether to stick with the 172.5mm crank or go ahead and get a 175mm crank. So the money is not the issue here.

Advice?

Ryanf

I use 175mm cranks. Long cranks are good for my diesel riding style. I'm 6'2".

jgeezer

I'm 6'3" with a 36 in inseam and have used 172.5, and 175 cm cranks. I have gotten good results from both. I prefer the longer crank because it slightly reduces the force that the leg needs to provide to produce a given amount of torque at the rear wheel. In fact I just went down and measured the two bikes I own with these cranks. By measuring from the saddle along the seat tube to the pedal center I got exactly the same length 39.5". This probably points up why crank lengths vary so little. In order to put your leg into the proper position to produce maximum sustainable force it is the saddle height and the position of your hips relative to the bottom bracket that counts more than the crank length.

At 5'11" I would think 172.5 or if you have long legs 175.

531Aussie

did you shove something right up your crotch to measure? Either way, that sounds more like it, and Kirby Palm's "21.6%" would therefore have you on 181mm cranks, which is very long.

If 33" is your inseam, I'd probably say stick to 172.5, but it sounds like you're curious to try the 175s, which obviously aren't crazy long, so it won't hurt to try them. Just be aware that longer cranks increase knee flexion, so your knees will be working a little harder. You'll most likely have to drop your saddle 2.5mm (assuming your seat is in the right spot at the moment), so, that, coupled with the 2.5mm extra through the top of the pedal stroke, means you knees will be coming up an exra 5mm at the top of the pedal stroke.

Robert C Wells

Yeah, I pulled the book up right into the jewels, but not so much as to be uncomfortable (I think it was the fact that she was measuring that made the difference).

Damn this bike fit stuff is just so complicated. Just a couple mm here, a couple mm there and everything changes. I just changed from 42mm wide handlebars to 44mm wide, much better, and from 100mm stem to a 130mm stem and then down to a 120mm stem. I may go back to the 130, not sure yet, gonna get a few more rides in on the 120 to be sure.

Point is, there are soooo many variables that need to be tweaked in order to acheive the proper fit for max performance and comfort.

I may just stick with the 172.5 as it's been okay so far. However, IF 175 would give me more power out of the same effort, and increase comfort, then it would definitely be worth the switch. But how to know for sure? Argh.

Here is a pic of my bike with seat height currently compared to the stem height (which I'm pretty much happy with):

Surferbruce

i'm 5'10" and run 172.5's i also run 165's on my fixed gear and have no probs.
i'd stick with 172.5's but if you're gonna go longer you might want to see if it will induce any toe overlap (which isn't a huge deal but a factor to consider none the less.)

Robert C Wells

Whoa Nelly! What is toe overlap and why do you have to confuse the issue even further?? (j/k of course)

531Aussie

what size it that bike? It looks a little small for someone 6ft, but if you have shortish legs for your height.....

There's no doubt fit is a question of mm, then, just when you think you've got it sorted, something changes 2 years down the track, then you feel like changing things around again.

I don't think you'd notice much leverage difference with 2.5mm; changes that small is more about changing to the size of the pedaling circle to match a preference, particularly for sprinters trying to get the feel they want at high revs. You might find the slightly larger circle more comfortable, but, as you say, you won't know until you try.

I came to the conclusion that longer cranks increase leverage, but they're harder to push because your knees are up quite a bit higher and slightly further away. Long cranks would be great if you could ride off the saddle all the time, which is why they're good for short climbs off the saddle, but they impact greatly on position when seated

531Aussie

that shouldn't be a problem. It's just when the toe goes past the level of the front tyre, so some people have to be careful when turning

Robert C Wells

Ok, that makes sense. I'm good with that.

As for the bike, it's 56cm, and the specs are on Trek's website if it helps. I bought the bike at a huge discount due to it being an '06 P1, and I don't know but what my LBS told me that it was a good fit b/c they wanted to sell it, which would really piss me off to know. That said, I did go through, I forget which website it was now, and used measurements that indicated that it would be a proper fit based on inseam, etc. It did indicate that the stem needed to be longer, and so I bought longer stems, and it definitely made a positive difference.

Oh, and I've always thought I had relatively long legs, compared to torso length anyway. At just over 6' with a 33" inseam, I still think that's long legs, right?

I guess all being said, I'll probably stick with the 172.5mm crank.

Thanks for all the advice.

531Aussie

oh, 56? It looks smaller. It must have a small head-tube. My smallest bikes are 56s
56 is fine, although I don't think you'd want any smaller.

as for long legs, I think you might be normal. I'm a smidge under 6ft (I'm 182cm), and my inseam is just over 35"

Old School

OK -- I'm 5'9" and ride a 58 cm Trek OCLV frame with FSA 175 mm cranks. Works for me!

stapfam

I have never bothered about crank length, just ridden the Length that came with the bike. However I got into road bikes last year and the Giant came with 165mm cranks- I am a short A&&. This year I built up a lightweight frame and Ordered 165mm crankset for it. Didn't check and just fitted it. Cleaning the bike last week and they are 172.5. I did not notice the difference The mountain Bikes have a variety of 170 and 175 mm cranks and Cranklength does not seem to worry me. Quality of the crankset does though.

cocoasprinkles

i'm 5 11" with an 87 inseam. I was riding 170 then jumped to 175. My knees enjoyed the change even after only one ride.