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How to decide Crank Arm length?...(4 posts)

How to decide Crank Arm length?...asphalt assault
Feb 15, 2003 5:28 PM
I'm going to be ordering Ultegra stuff for the bike I'm building and don't know what length cranks to get.

What do you take into consideration?

I'm using 2 rings in front. There isn't much climbing here in flatland northern Illinois/northwest Indiana where I live. I don't plan on racing, the bike will be mainly used for training...maybe a century or two. I weigh 200 and would consider myself more of a masher then a spinner, I like to get out of the saddle and hammer.

Any clues? When it comes to road stuff...I'm a bit clueless; )

Thanks for your continued support!
re: How tall are you?cyclopathic
Feb 15, 2003 5:41 PM
fitting guides recommend 170mm for under 5'5"-5'6", 175 for over 6'-6'1 and 172.5 in between. In reality it's more of personal preference I am 5'5" and I ride 175 and 170, not much difference
Ugh the crank arm debate... just go with 172.5PODIUMBOUNDdotCA
Feb 15, 2003 11:34 PM
The crank arm debate shows its head again. I hate this debate cus everyone has their opinions on crank arm length vs height and all this stuff and not all of it is true. Heres my logic to just go with 172.5:
1) 172.5 is the standard. Almost everyone uses them.
2) 2.5 mm is 1.5% of 172.5... 1 inch of a 6 foot tale individual is about 1.4%. Double that for the lower body only. So this means any deviation for about 6' up or down for every inch you should change the crank arm length about 5 mm. So if people have the same inseam someone 6'4 should ride 192.5 whereas someone 5'8 should ride 152.5. Then someone 5'0 should only ride 122.5. Realistic? Not at all.
3) On the track I know guys who switch their cranks out and have forgotten to change their cranks... in the process they have done pb's with crank arm lengths they shouldn't have been able to do them on in "theory".
4) The previous poster even says he notices no difference between 170's and 175's.

Cranks were never really designed to match height... guys like Sheldon Brown (who at this stage is a bike guru who doesn't race) think its relevant but thats his 2 cents and I disagree with him.

So in conclusion just go with 172.5. Give yourself a challenge while riding and begin to speed your cadence up... this will give you a good challenge.

My 2 cents,
Thanks Guys...asphalt assault
Feb 16, 2003 4:29 AM
...I'm 5'9", I guess I left out the most important piece of information!

Looks like I'l go with the 172.5 length.