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Crank Arm length(8 posts)

Crank Arm lengthgatr
Mar 18, 2001 4:53 PM
Any thoughts on Crank Arm Length ? I run 170's ...thinking of trying 172.5's ....
re: Crank Arm lengthAkirasho
Mar 18, 2001 5:22 PM
There are tons of theories and opinions about crankarm length... but this site might give you enough data to compare, contrast and decide for yourself what might work best.

http://www.analyticcycling.com/PedalOpCrankLength_Page.html

Be the bike.
Interesting site. But what the hell do you do with it?bill
Mar 20, 2001 11:50 AM
I dutifully plugged in some measurements, and I got some data, but I'm thoroughly confused. Now, maybe if I spent more time with it to figure out what it's showing me, it may mean something, but, can you help me? I thought it would sort of say "170" or "172.5" but it didn't. Can you help me figure out what I've learned?
That's because even the experts can't agree ...Humma Hah
Mar 20, 2001 2:51 PM
... and the only way to tell is to try it and see how it works for you.

There does seem to be some evidence that "good spinners" may do better with shorter cranks, while folks who naturally have a slow, powerful pedal stroke and long legs may do better a little longer. I did read one study done on ergometers that really surprised the researchers. They found that many riders had measurably better power output with short cranks than the conventional wisdom said should be true. They tried cranks down to something like 160 mm, and the shorter the cranks got, the better those riders did. That's what convinced me to try a set of 160's -- I adapted to them easily and they worked well for me (I use them off-road where the extra ground clearance is a blessing).

And your riding position on the bike has something to do with it. If you ride with really low bars, for example, longer cranks will bring your knees closer to your chest (but it will be hard to tell if it is only 2.5 mm). Someone making a 10 mm change who is already nearly banging their knees into their chest might need a geometry change. For me, going from 160 mm to 175, I can feel a "drag" in my legs: the extra bend in my knees seems to rob some power, probably because of all the squishing action that goes with the greater flex.
I think you'll hardly notice ...Humma Hah
Mar 19, 2001 11:03 AM
... I swap between 160's, 170's and 175's on one bike, depending on the kind of riding.

I don't notice much difference going from 170 to 175, other than a little loss of pedal clearance on corners. But going directly from 160 to 175 is noticable, the extra bend needed in the knees is apparent, although I get used to it in a day or so. I really don't notice the change in leverage.
you don't know that!Jiggy
Mar 20, 2001 4:28 PM
some people notice small changes... I, for instance, cannot tolerate a change of only 2.5 without some knee discomfort. Remember, the leg is not only bent more at the top, but extended more at the bottom (provided saddle height has not been altered).
You're right, I don't ...Humma Hah
Mar 20, 2001 5:48 PM
... but that's the nature of the problem. You make a small adjustment, you try it, if you don't like it you pull the crank arms off and go back to the originals, or try going the other direction.

As a matter of fact, I did a century early in February on my 170's, no problem with my knees. I did one March 10, using my 175's, and my left knee started killing me at about 60 miles. Which could be the crank length. Good thing I've got a wrench ... I'm planning to swap 'em.

Generally, I'm of the opinion that shorter is very much worth a try -- it tends to do a slightly better job for me.

But most people who've tried a 2.5 mm change don't seem to find it makes a noticable difference.
re: Crank Arm lengthlook271
Mar 19, 2001 12:31 PM
There's no real evidence that it makes any difference. If you like the feel of the 170's, stick with them. If not, go with the 172.5's. I went from 170's to 172.5's and noticed little difference. I now run 175's and I can definately tell the difference with them. As for climbing, speed, etc.? I can't really say that it's made a difference.