# Crank arm length? 170mm, 172.5mm, 175mm?



## tojnom (Feb 29, 2008)

How do you determine which crankarm length is right for you? 170mm, 172.5mm, 175mm?


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## FatTireFred (Jan 31, 2005)

little guy- 170
big guy- 175
somewhere in between- 172.5


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## cww180 (Aug 31, 2008)

It seems that from the maker a 54 starts the 172.5 crank under is the 170. I have hear that even if you have a 50 or 52 the 172.5 can be better when climbing hills.


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## tom_h (May 6, 2008)

*numerous posts on 'crank arm length'*

http://forums.roadbikereview.com/showthread.php?t=137802

and especially what Kerry Irons wrote.


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## Fredrico (Jun 15, 2002)

The longer the crank arms, the better leverage you get, which is why 175s are great for climbing. Most serious MTBs have 175s for that reason. Shorter arms are easier to spin, though. Your legs scribe a smaller circle. Trackies use 165s to clear the banked track, but also to develope insanely fast cadences on their one speed fixies.

For the average height roadie, 5'6"-5'10", 170s or 172.5s are a good compromise between ability to spin and decent leverage when climbing. Taller guys would be able to spin 175s easily, and even 180s, especially on a time trial bike.

I'm a hard core spinner, even climbing, and have always preferred 170. If I were into big gear mashing, I'd go with 175s, no question. I'm 5'8" tall.

Keep in mind, the difference between 170 and 175 is half a centimeter or about 3/8ths of an inch.


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## CleavesF (Dec 31, 2007)

I think crankarm length is garbage. I've used 165mm to 175mm and honestly, I can't tell the difference. 

If it has any drastic effect on my cadence, I can't tell. Thank you gears! I don't really get the height analogy. This is because if your crankarms shorten, you can always increase your seat height and vice versa. 

I run 165mm, 170mm, 172.5mm, and 175mm. Yeah, 1 cm of range. I'm stupid like that. That' what I get for owning 5 bikes.


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## SystemShock (Jun 14, 2008)

FatTireFred said:


> little guy- 170
> big guy- 175
> somewhere in between- 172.5


That'll work, but some big guys even like 180s, and some medium-sized guys will take 175s over 172.5s. Very little guys & small women prefer 165s sometimes.

There is some personal pref involved.

...


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## mikeyp123 (Mar 9, 2007)

I too can't tell the difference between the 172.5 on my roadbike and whatever my fixie has. When I road a 175 the only issues I had was the knees coming up higher, and closeer to the chest when riding in an aggressive position.. didn't like that.


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## Andrea138 (Mar 10, 2008)

SystemShock said:


> That'll work, but some big guys even like 180s, and some medium-sized guys will take 175s over 172.5s. Very little guys & small women prefer 165s sometimes.
> 
> There is some personal pref involved.
> 
> ...


Yep. I ride 172.5mm cranks (54cm bike). I've ridden around on my guy's CX bike (with the saddle prettymuch sitting on the top tube) with 175mm cranks & liked how those felt, but would get even more toe overlap than what I've got now. I tried a friend's bike w/165s & felt like I was riding a tricycle.


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## iliveonnitro (Feb 19, 2006)

34" inseam and I ride 170s as a sprinter. Although the difference of 2.5mm is negligible, I love that the 170s. More aero since I'm not too flexible, better spin, and helps balance my "snap" with some top-end speed.


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## SystemShock (Jun 14, 2008)

I would just add that I've ridden 170s, 172.5s, and 175s extensively, and CAN definitely tell the difference between them.

2.5mm doesn't seem like much... but that's just the crank arm. The _pedaling circle_ is actually changed by about 16mm by a 2.5mm increase or decrease in crank length. 

Let's put it this way... 170s feel a bit small to me, 175s feel 'powerful' and torquey but I can't spin 'em too well, and 172.5s?.... ahh, just right. 

(I ride a 54cm frame)

...


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## flyjoe (Mar 17, 2008)

I have 170's 175's ands a set of 180's. I can tell from 170 to 180 but it doesnt cause a problem , it only takes a minute or two to adjust.but that could just be because there on diferent bikes. it really doesnt seem to matter to me.


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