Crank arm length??????

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11.4
Posts: 1095
Joined: Tue May 23, 2006 4:33 am

by 11.4

Your longer cranks result at the top of the stroke in a more extreme hip flexion angle. That's not all that efficient, it may also have the top of your thighs impinge on your abdominal muscles and diaphragm, and it accentuates your knee angle too -- your knee ends up higher, all else being the same, which means the angle is greater. None of these are particularly good. So if you move your hips forward and increase the height a bit, it eases these issues. You can't go too far because you have the bottom of the pedal stroke to deal with in terms of reasonable leg extension, plus if you move forward you are accentuating the knee angle and related issues at the 9 o'clock position (farthest back position). In short, you don't have a lot of room to adjust and the range gets smaller with longer cranks. If you use biometric fitting and try different crank arm lengths, you notice how a rider's pedaling and power both deteriorate rapidly as crank arms get longer. I think that's probably what you're seeing.

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Rick
Posts: 2034
Joined: Sat Aug 29, 2009 4:30 pm

by Rick

There is no question that 60mm cranks would be inefficiently short, and no question that 400mm cranks would be inefficiently long.
So between the two extremes, the real question is whether the "optimum" length is 150 -ish or 190 -ish, or where in between.
And then how critical is being exactly optimum.

There is only ~1.4% difference between 172.5 and 175, so I suspect that most people either don't really notice any difference or that any perceived difference is really due to other factors. It is really difficult to do a controlled, double-blind experiment on such a thing. So in absence of well-corroborated data, I don't think there is any harm in self-experimentation and your conclusions will be just as valid FOR YOU as anything. It is sort of expensive to try numerous cranks though.

My re-experimentation with 180mm seems to be going OK....no knee problems or anything. But it is the dead of winter, so I am not riding as much and my motivation to try to produce "high power" is completely absent.

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wheelsONfire
Posts: 6280
Joined: Mon Jul 07, 2014 8:15 am
Location: NorthEU

by wheelsONfire

Thanks for input guys :thumbup:

I don't feel any decrease or mentioned issues 11.4, but as mentioned, i only moved up by 2.5mm in cranks lenght.
I don't feel cramped or find any issues with movement, either at hoods or in drops.
But i have to agree with Rick. It is winter, it's not really so that i can hammer away or corner in full speed. Neither have i done longer rides as i do in the summer.
My mere suggestion is that i can move more with shorter cranks, it seems like a good thing i agree. But at the same time i never felt i had an optimal position that came natural.
I always seemed to change something, always wondered why something felt good at one point just to be changed the next times.
This has been a constant behaviour more or less.
I have been suggested positions, but i wasn't on them for very long, simply because they did not feel good.
I have even changed frame sizes a few times, played around with stack and reach, stems lenghts and angles and heights (on all sizes of my frames).
I have 3 shoes (Giro Factor) i can set up differently (cleats), sure i can ride most positions, but it was a question of time until next change (small changes though)!

Years ago i had a MTB with 177.5 or 180mm cranks (don't remember), but that surely caused a problem.
I surely noted that saddle could not be in sufficent height cause it became a problem on the downstroke.
Lower saddle caused the opposite problem.
My GF at the time, had a smaller sized bike with 167.5mm cranks and that bike felt very snappy. The downside was perhaps that i could never ride very fast on it.
After that, i always rode 172.5mm cranks but were many times told i should have 175mm cranks. I am slightly over 89cm in inseam measuring barefeet from floor to crotch, feets 25cm apart C-C of foot.

Perhaps it's within margins of reason, but for now i feel this was a step in the right direction for me.
Bikes:

Ax Lightness Vial EVO Race (2019.01.03)
Open *UP* (2016.04.14)
Paduano Racing Fidia (kind of shelved)


Ex bike; Vial EVO D, Vial EVO Ultra, Scott Foil, Paduano ti bike.

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