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 Post subject: Crank arm length??????
PostPosted: Fri Oct 03, 2014 12:52 pm 
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Location: USA
What is the concensus on crank arm length. I live in a hilly region... climb quite a bit. My thought with the longer length there is better leverage. I am 6' tall and have been using 175's and would like to try a 180. Is there a downside to my way of thinking or trying the 180's. Thank you.


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 Post subject: Crank arm length??????
Posted: Fri Oct 03, 2014 12:52 pm 


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PostPosted: Fri Oct 03, 2014 1:22 pm 
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Joined: Sun Jun 18, 2006 10:29 am
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There has been a huge debate on the issue... the outcome is it does not really matter that much. It has more to do with your ride style. 175 is fine for your height IMHO.

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PostPosted: Fri Oct 03, 2014 1:48 pm 
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One of the most debated topics in cycling, on which there is no consensus.

I'm 6' 1" with long legs and have bikes with cranks 175 - 177.5 - and 180.

Cannot really tell the difference to be honest.

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PostPosted: Fri Oct 03, 2014 1:58 pm 
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Similar to bore/stroke design in an engine. Longer crank gives more torque and makes it easier to turn a gear, but each stroke is longer and tends to reduce cadence. Its a tradeoff.

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PostPosted: Fri Oct 03, 2014 5:39 pm 
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I use 175 mm and I am 5'7. I don't see why not go to 180 mm if you live in hilly region.


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PostPosted: Fri Oct 03, 2014 6:06 pm 
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Just my experience: I am one who thought crank length should make a difference. It only makes sense.
So I have tried over the past few years 170, 172.5, 175, and 180s. (I have a 33.0" inseam = 83.8 cm)
Even on 25-30 minute climbs averaging 10% it hasn't seemed to make a significant difference. (Using average power and times)
Yes it is a little easier to push a big gear at low cadence on the longer ones, and yes the shorter ones seem a little easier to spin, particularly going "over the top" at high power outputs. But I conclude that over any significant length of time you are limited by your biochemical power output, so the crank length effects are swamped by other things.
I am currently using the 170's, because I figure that if it makes little difference I might as well have a comfortable spin.

But I might continue experimenting, because it seems like it just has to make a difference! Right ?!?!? :noidea:


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PostPosted: Fri Oct 03, 2014 6:16 pm 
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Like Bikerjuilo says, no consensus. I'm 6'1" (91cm inseam) and use 175 cranks. On the tt bike I opted for 172.5 cranks.
Longer cranks give more raw leverage and for a short punch that's ok, but probably something to be said for more constant spin of a smaller circle as well. Best all round for me seems to be 175 but I'm sure I wouldn't notice much of a difference with 172.5 either (have those on my very first higher end road bike). All depends on what you're doing I suppose and you're riding style. No consensus means try it out for yourself. It's never a bad thing to experience it for yourself as opposed to just follow consensus like a lemming.

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PostPosted: Fri Oct 03, 2014 6:52 pm 
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Location: USA
Thanks for the input.. very interesting and now thinking of not changing. Thanks


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PostPosted: Fri Oct 03, 2014 7:04 pm 
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Joined: Sat Sep 22, 2012 2:22 pm
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What with this being Weight Weenies then it stands to reason that the shorter arms will be lighter! :-)


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PostPosted: Fri Oct 03, 2014 7:25 pm 
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Quote:
What with this being Weight Weenies then it stands to reason that the shorter arms will be lighter


haha, that is funny and true.

I will be going from 175 to 172.5 when my new cranks arrive.

As I see it, not only do yor knees come up hiher causing a crimp but also more your knees are more compressed or extended when the crank is horizontal. For me I think I will prefer my knees being less crimped when the longer crank is in the vertical and horizontal/hind position. also, could one apply more force when the shorter crank is in the horizontal/fore position, as the leg is not so extended? straighter leg meaning more direct force.


Last edited by bigfatty on Fri Oct 03, 2014 7:56 pm, edited 2 times in total.

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PostPosted: Fri Oct 03, 2014 7:27 pm 
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I've bored several forumites over the years with my stories about this, :D so here's the short version.

I'm 6ft with long-ish legs (89cm inside leg), and I've extensively used every length from 170 to 180, and in the last couple of years I've done 'some' riding with 165s (mostly to see if I could get more aero), especially when I had a sore knee. Around 2004, I gave 180s a good try for over a year, but they ended up annoying me (mostly due to the position they put me in), and I went back to 172.5s for most of my riding. I probably would've been just as happy returning to 175s, or even 170s, but there were more 172.5s available in Dura-Ace 7800s around here when I was "re-decking" out my bikes.

In short, I believe longer cranks probably provide a small leverage advantage when riding off the saddle, but when seated, there's a trade-off: while there may be more leverage, they're harder to push, basically because your knees come up higher, and, to a lesser degree, you have to pedal a larger circle. In other words, when seated, it's much of a muchness.

In my opinion, the "spin" thing is only an issue if you're a sprinter.

One potential drawback I found is that long cranks can be seductive when you first try them, because they can feel good and "liberating", so you try everything to make them work.

Here's a short article which briefly explains the conundrum between possible reduced force (extra leverage?) versus the extra torque required to pedal a larger circle when using longer cranks.
http://www.arniebakercycling.com/pubs/F ... Length.pdf


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PostPosted: Fri Oct 03, 2014 9:42 pm 
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Joined: Wed Oct 30, 2013 12:52 am
Posts: 240
I used to commute 35mile each way to work on a track bike with 165mm cranks - 1-2 days a week. I would then ride my road bike with 180mm cranks. I stood much more on the road bike and also was not on a fixed gear and would use bigger gears (duh). I am 6'2".

Anyway I thought the 165s made my 180s feel better. I didn't like 165s on my road bike. Now I ride 175s as a matter of course and average around 85-90rpm. I would likely choose 172.5s for crits and spin 5 rpm faster.


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PostPosted: Fri Oct 03, 2014 10:29 pm 
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Joined: Mon Jul 13, 2009 9:19 pm
Posts: 276
Location: Denmark
I agree with User Name and bigfatty, my inseam is 84 cm and using 170mm , my bikefitter said: I'd like to see you on 170 mm" so I skipped the 172,5 mm and have been a happy man ever since. I don't believe in riding style, I believe in body mechanics.
The size of your feet is also a factor when determing the crank lenght.


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PostPosted: Fri Oct 03, 2014 10:37 pm 
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Joined: Fri Oct 28, 2011 3:25 am
Posts: 906
Location: United Kingdom of Great Britain and Northern Ireland
My advice to anyone serious about their cycling is to try the crank length that the math/maths says suits you best, and then also to try the next size up.


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PostPosted: Sat Oct 04, 2014 12:50 am 
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Joined: Mon Jul 21, 2014 5:02 pm
Posts: 3
My two cents: longer cranks aren't better. They've done studies that show no significant change in power within a pretty huge range of lengths (something like 160-190) and longer cranks will compromise your ability to produce power when in a low aero tuck. Longer cranks will drive your knees into your chest and make for a very tight hip angle. I'm 6'1", saddle height 83.8cm and will be running 172.5 cranks on my road bike and 165 cranks on my TT bike next season.


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Posted: Sat Oct 04, 2014 12:50 am 


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