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crank arm length(7 posts)

crank arm lengthbikapelli
May 10, 2001 2:52 PM
I've been riding seriously for about 8 years and on all my bikes I have 175 crank arms. I purchased a Bianchi over the internet and it came with 172.5. Figuring I would just change them out I decided to ride it a couple of times. I was very surprised to find that my spin I had been working on for the last year was really working with the shorter crank arms. I climbed better and had my best TT results with this set up. I'm now thinking af changing my other road bikes to 172.5. One of which is a custon and I was told that 175 was the way to go. I'm 6'. Has anyone out there changed crank arm legth after riding several years with a specific size?
re: crank arm lengthmdooley
May 10, 2001 3:13 PM
I use a 175 and love it, wouldn't change.
How can you tell its the cranks and not the bike...Bruno S
May 10, 2001 3:52 PM
You have changed to a new bike, could the better times and climbing be the result of other factors besides the cranks lenght? The difference between cranks is only 0.098". For your height 175mm it the recommended lenght.
re: crank arm lengthStanley
May 10, 2001 4:09 PM
Go with the 172.5. I'm also 6ft (88.4 cm inseam)tall and have gone back to shorter cranks because I have way less back pain and a smoother pedal motion particularly at the end of races. If it feels better go with it. This myth of crank length relative to leg length is way over done. What counts is effective crank length. This is governed be femure tibia ratio, foot size and prefered pedal motion. I have a long effective crank length as I ankle alot. The other issue - I think should be considered - is the way ones muscles insert into the legs and so on. It may be that some peoples muscles allow for a more fluid movement over a greater range of motion. (I will think that one over to clarifiy it a bit. Anyway, go with the 172.5s
re: crank arm lengthPhil2
May 10, 2001 10:48 PM
This article by Lennard Zinn blew my mind: http://www.velonews.com/tech/rev/crank.html
re: makes sensecyclopathic
May 11, 2001 9:13 AM
you are more efficient with shorter cranks. Upper part of the stroke is less efficient, by using shorter cranks you reduce motion range = more efficiency.

The max power part /power output the same for diff crank length/ could be explained by that simple fact that your output is limited by heart/lungs/muscle capacity

WHat I get kick out of is that this by any means is not contradictory with previous climb test /which showed that longer cranks yield faster climbing/. Yes they are less efficient /look #1/, but they help you to produce higher power output at LT. why? through wider motion range load spread to more muscles. Even with higher HR, less efficiency you still producing more power.

The other explanation could be that HR depends on cadence. Using longer cranks allows to use lower cadence /my HR at 110-120rpm is ~5-6bpm higher then at 60-70/ See where am I getting at? you just work harder and climb faster.

both of conducted tests are faulty:
- HR is not good indicator of load /I am hitting 170bpm going downhill on mtb and I am NOT pedaling/
- cadence is not taken into consideration. 90rpm could be too low for one tester and too high for another one.

the best test would be 6mi gradual hill time trail with diff cranks and diff cadence. Hill cannot be too steep or you get geared out, you need to be able to sit and spin 120rpm if need.

my .02$
re: crank arm lengthDoc
May 11, 2001 6:10 AM
I've had a similar experience. After 6 years on a carbon Al Trek 2200, I had a steel custom built up with longer cranks: 175, instead of 172.5. My cadence has increased, as well as power, but so has comfort and everything else. My current bike is just a much better bike, and, of course, it's new and different.... By the way, I'm also six feet tall. I think that with a new bike and so on, there are just too many differences to be able to blame much on crank arm length.