Crank Size



mgkaplan

New Member
Apr 23, 2006
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I have a Giant OCR C3 which I purchased off the shelf. The crank size is 175.

I compared it to my old 1986 vintage custom built Guerciotti/Dura Ace bike and noticed that it has 170mm cranks.

Is the crank size something that I need to be concerned about?

Would it be a good idea to get a professional fitter to sort this out for me?

Thanks
 
netscriber said:
I know Kirby Palm has put a bit work into that site (the 2nd link) -- and I'm not shooting the messenger :) -- but I really think it's rubbish: 21.6% of inseam is way too long, especially for riders over ~5ft8". I'm 6ft, and I tried 180mm cranks ,which ended up being too long, but Kirby Palm's formula would have me on 193mm!! Every time I type that, I realize more and more how TOTALLY rediculous it is. ANd he's NO athlete!! :D http://www.nettally.com/palmk/kirby2.jpg

The first link, and the traditional advice is better. I tried all the long crank stuff for nearly 2 years, and it didn't work out.

to answer the question, going up a length by 5mm or more should be a concern. Too long a crank can stuff up your position and/or your knees.

The easiest way to sort it out is to measure you're inseam, and it's not 'pants' inseam. :)

here's another traditional guide.

http://www.bikefitting.com/English/Theory/Crank.aspx

this chart is traditional, but a little less conservative than others

inseam ..........Crank Length
60 to 65cm..............150mm
66 to 70cm .............155mm
72 to 75cm .............160mm
75 to 78cm .............162.5mm
79 to 81cm .............165mm
82 to 83cm .............167.5mm
83 to 86cm ..............170mm to 172.5mm
87 to 90cm ..............175mm to 177.5mm
91 to 94cm ..............180mm
94cm plus ................185mm
 
It appears that all of these charts and formulas point to a 170 - 172.5 crank size for me, given my dimensions.

My current bike has a 175mm crank. Should I consider this a problem?
 
mgkaplan said:
It appears that all of these charts and formulas point to a 170 - 172.5 crank size for me, given my dimensions.

My current bike has a 175mm crank. Should I consider this a problem?
I do not know how serious of a rider you are, but here's something to consider. Trackies use shorter cranks(shorter than their recommended size) because they use higher RPMs and need lesser force. The exact opposite of that is some people I know(a couple of pros) that use cranks longer than they need(and they are climbers).

Are you facing a problem right now? Do your knees or anything else hurt? Do you feel like you could put some more power either way?
If you have a real problem its a problem unless you are a pro and minute little things matter because you are gaining or losing seconds on someone.
 
netscriber said:
I do not know how serious of a rider you are, but here's something to consider. Trackies use shorter cranks(shorter than their recommended size) because they use higher RPMs and need lesser force. The exact opposite of that is some people I know(a couple of pros) that use cranks longer than they need(and they are climbers).

Are you facing a problem right now? Do your knees or anything else hurt? Do you feel like you could put some more power either way?
If you have a real problem its a problem unless you are a pro and minute little things matter because you are gaining or losing seconds on someone.
It doesn't feel like a problem. Nothing hurts. However, I am thinking of replacing my cranks with a much lighter set. Of course I want my upgrades to be the appropriate size.
 
mgkaplan said:
It doesn't feel like a problem. Nothing hurts. However, I am thinking of replacing my cranks with a much lighter set. Of course I want my upgrades to be the appropriate size.
Given what you said above, my gut feeling is that you should be perfectly happy with either a 170 or 172.5 crank. The 175 probably works too, but might be at the long end of what is best for you. As others have said, things depend a lot on what it is you want to do. If you are into serious racing, or want to go there, then a different set of criteria applies, but for a hobbyist, even a serious one, any of the crank lengths mentioned above should work fine.
 
mgkaplan said:
It doesn't feel like a problem. Nothing hurts. However, I am thinking of replacing my cranks with a much lighter set. Of course I want my upgrades to be the appropriate size.
Then you've answered your own question. Just find the right size and buy it.
 
mgkaplan said:
It doesn't feel like a problem. Nothing hurts. However, I am thinking of replacing my cranks with a much lighter set. Of course I want my upgrades to be the appropriate size.
.
I went from 170 to 175 only because the bikes I bought had them. I had not really given much thought to CL as I probably didn't know any better at the time. So I lowered the saddle 5 mm & off I go.

The first thing I noticed was the bigger pedaling circle of the 175s, about a month for that to feel better, still not good but better, & I felt a lack of power as I started the down side of the pedal stroke particularly up hill. The 5 mm difference makes 10 mm higher knee position & if you go for KOPs positioning that would increase even further the knee angle at TDC. Gradually I raised the saddle 2 mms at a time till I felt I had more power just after TDC but I am so high that I'm sure I have sacrificed power at the bottom.

I have done just shy of 5k klms on the 175 & I still don’t like them. Kirby Palm would have me on 180 cranks [83cm inseam X 2.16 = 179.3] & conventional wisdom 172.5 [83 X 2.08 = 172.6] When the time comes I will go for 172.5 as I think that is the correct size for me. I am also a spinner which by all reports suits a shorter rather than longer crank arm.
 
Albert 50 said:
.I went from 170
jeez, I'd say 170 would be your absolute maximum. My inseam is 89.5cm, and I'm still tossing up between 172.5 and 175.
 
531Aussie said:
jeez, I'd say 170 would be your absolute maximum. My inseam is 89.5cm, and I'm still tossing up between 172.5 and 175.
Yeah, I agree. If I were you, I wouldn't suffer on those cranks for more than one ride, and get 170s right away.
 
mgkaplan said:
I have a Giant OCR C3 which I purchased off the shelf. The crank size is 175.

I compared it to my old 1986 vintage custom built Guerciotti/Dura Ace bike and noticed that it has 170mm cranks.

Is the crank size something that I need to be concerned about?

Would it be a good idea to get a professional fitter to sort this out for me?
Let me begin by reassuring EVERYONE that I am not going to recommend a crank length to you OR anyone!

I will just make the observation that there are a lot of riders who have a 175mm crank on their mountain bike while possibly having a different length crank on their road bike ... just think about it.
 
alfeng said:
I will just make the observation that there are a lot of riders who have a 175mm crank on their mountain bike while possibly having a different length crank on their road bike.
yeah, and they shouldn't have. There are too many short guys out there riding around with their knees in their chest.

here a Carmichael's recommendations:


inseam..........crank length
<29"..................165mm
29" to 32"...........170mm
32" to 34"...........172.5mm
over 34"..............175mm
 
531Aussie said:
here a Carmichael's recommendations:


inseam..........crank length
<29"..................165mm
29" to 32"...........170mm
32" to 34"...........172.5mm
over 34"..............175mm
Another thing to keep in mind is that all of the inseam based formulas and tables assume that everyone has exactly the same ratio of femur length to tibia length to shoe size. I wouldn't use them for more than a starting point. All that matters in the end is that the cranks feel right when you're riding.
 
artmichalek said:
All that matters in the end is that the cranks feel right when you're riding.
Amen to that. Since the OP said that he finds his long cranks uncomfortable, he should get shorter ones, no matter what the tables say (although, in his case it seems the tables agree with that recommendation).
 
According to this i would need 160-165mm cranks (i am small, only 28.5" inside leg, ive even got a tiny 44cm compact frame).

Does anyone know what manufacturers would make cranks in this size? I currently have 170mm and would like to try smaller ones.
 
alvynmcq said:
According to this i would need 160-165mm cranks (i am small, only 28.5" inside leg, ive even got a tiny 44cm compact frame).

Does anyone know what manufacturers would make cranks in this size? I currently have 170mm and would like to try smaller ones.
Shimano, SRAM (Truvativ), FSA, Stronglight, Bontrager are some manufacturers that offer road cranks in 165mm length.