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Old 06-21-06, 11:35 PM   #1
mgkaplan
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Crank Length

I recently learned that my current bike (Giant OCR C3) has a 175mm crank. My old custom bike has a 170mm crank. I am 59 years old 5'11" and have a 32.5" inseam. Something tells me that my cranks may be too long. Does anyone here have any experience in determining the correct crank length?
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Old 06-22-06, 12:38 AM   #2
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Quote:
Originally Posted by mgkaplan
I recently learned that my current bike (Giant OCR C3) has a 175mm crank. My old custom bike has a 170mm crank. I am 59 years old 5'11" and have a 32.5" inseam. Something tells me that my cranks may be too long. Does anyone here have any experience in determining the correct crank length?
By all the "Rules" on crank length, I should be using a 165mm. Never had one but used to stipulate 170 for all new bikes or replacements. Then I got the Tandem and this had 175 fitted. To be quite honest- I never noticed the difference and I tried several bikes fitted with 170 or 175 cranks fitted and my legs are not that critical. I cannot tell what cranks I am riding just by feel, effort or extra pain.

In any case- with an inseam 3" longer than mine- By all the "Rules", you are probably about right.
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Old 06-22-06, 01:53 AM   #3
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My experience is that if your seat never feels like it's at the right height -- either a bit too high or a bit too low -- then the cranks are too long. For me, at 5'10", 175s are a bit too long, but not a big issue. 172.5s are perfect, and 170s are fine.

And yes, I can feel the difference between the three. I spin in an easy gear, so the slightest change is noticable due to my cadence.

Last edited by Big Paulie; 06-22-06 at 02:57 AM.
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Old 06-22-06, 06:11 AM   #4
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Most calculations put me right on the border of 170 and 172.5mm. But on my lowracer I am using 155mm and having pretty good luck with it. I'm finding that I don't have to bend my knees as much, and my feet don't have to move in such large circles to get me down the road. My cruising and top speeds seem to be about the same (compared to 170s) and my climbing is better because I can stay on top of the gears better. The increased rpm from the smaller pedal circles means I can run about a gear lower for any given speed. When the hill gets so steep that I am winching myself up, I may need that extra gear lower because of the shorter leverage arm, but that's pretty rare anyway.
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Old 06-22-06, 07:31 AM   #5
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On my first road bike it was recommended that I ride with 172.5. However, I seriously doubt I could tell between those and a 175... 2.5mm?
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Old 06-22-06, 07:36 AM   #6
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A lot it probably is what you get used to from a "spinning" perspective. If you're accustomed to one size or another then I'd suggest sticking with it. I ride 175's which is also a good fit for me. I borrowed a buddy's bike for a month when mine was in the shop and he rode 170's. While it was a different frame and setup, the different crank sizes was the thing I noticed the most. I could not wait to get back to the 175's.
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Old 06-22-06, 08:12 AM   #7
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I am 5'10" 181 # and for years I have used 172.5 with never a problem, my inseam is 33'
About a year ago I went 175 on the cranks, maybe it was physcological but I felt a difference in my spin seemed to be like a lug or having to pull more on the up-stroke .
I wnt back to 172.5. go with whatever is the most comfortable for you and your knee's
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Old 06-22-06, 09:36 AM   #8
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I've used 170, 172.5, and 175. Never noticed any difference. Others may be more sensitive...
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Old 06-22-06, 10:20 AM   #9
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I'm only 5' 7", have been using 170mm crankarms until I got the Lemond which came with 175's.
Seems odd that Lemond would spec a 53cm traditional steel (non-sloping) frame with these long crankarms.
Have not had a problem with the extra length even on long rides, although it does slow my spin a bit.

Given a choice...I would choose 170mm.
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Old 06-22-06, 07:49 PM   #10
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I think "rules" for crank length are way over rated. There are just too many variables that can't be taken into account by rules. Inseam size; height; length of lower leg relative to upper leg; muscle mass; foot length; do you point toes or pedal with foot flat; how many degrees to you point toes; if you spin at what rate; are you bent over enough to put your lower back muscles fully into each pedal stroke and how does this impact on your spin; what kind of pedals and cleats do you use..... and on it goes. I think there is real value in trying to find people with different crankarm lengths and seeing if you can try 'em out. After having ridden 165's, 170s, and 175s, I find that I'm most comfortable on 172.5. Why? I don't really know. They just feel more natural to me.
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Old 06-22-06, 08:14 PM   #11
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I'm 6 feet tall, with a 32 or so inch inseam-- I ride a fixie with 165s, and two road bikes with 172.5s. Can I tell the difference? probably, but its not really noticable. A riding buddy did comment on the fact that on my fixie my knees don't come up nearly as much-- go with what feels the best, or stick to what you have, and use the others fo r specialty items-- the fixie has 165s to reduce the chance of 'bottoming out' on your down stroke when going around a corner--you can't contrpl which leg is up or down, as you can't coast on a fixie. That is why track bikes tend to have slightly higher bottom brackets and shorter cranks.
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Old 06-24-06, 03:23 PM   #12
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Somehow, at sometime, somewhere I read something that convinced me I needed 175mm crankarms. I have a 31-32" inseam. I bought them; I tried them; I thought I'd wrecked both knees. I only use 170's.
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