Crank Length

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xena
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by xena

GCN did a test and it really made no difference.
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mr4fox
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by mr4fox

Two things I wonder about are
1) what happens when you're on a long steep climb and in youre at threshold in your lowest gear but your power:weight vs gradient means you can't spin you preferred optimal cadence because it's to steep...or you go way over threshold and crack before the top?.

What difference does crank length make then?

And 2) did the GCN train on each crank length for a period of weeks/months to see if any adaptation occurred? I can't remember but I don't think they did. I raise this point because I know changing from round to oval chainrings takes time to adapt to. Changing back also takes time. I know its not exactly the same thing but both changing chainring shape and crank length alter the muscular/physiological production of torque....makes me wonder.

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cyclespeed
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by cyclespeed

xena wrote:GCN did a test and it really made no difference.


In the video I saw, they were confused by the results they obtained, then effectively declared them null and void by saying that they had not changed gear at all between the tests. But they still managed to conclude that shorter cranks were a good thing, although not sure how they arrived at that conclusion.

mattr
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by mattr

There are actually some proper tests around on the net. Rather than a GCN video.

They basically say the same thing. Crank length makes little or no difference.

Bogan
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by Bogan

I believe there is another factor, whether you are a spinner or not. I am not, hence i believe I get more engineering advantage with longer cranks. I generally have a cadence of between 80-90. I can only maintain a cadence of 110-120 for a short period of time. It is a function of leg speed and age!
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cyclespeed
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by cyclespeed

To those saying crank length makes no difference, if you were forced to ride on 140mm or 200mm cranks would you be comfortable with that?

Although those are extremes, at what point DOES crank length start to make a difference? It's true that going from 175 to 172.5 is not going to make a big difference - debatable if it could be measured or felt. But going from 175 to 165 would make a discernible difference, which just leaves the question, is it a good difference?

xena
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by xena

It's kind of similar to the oval crank debate
It really makes hardly any difference. Look how many riders switched back to normal rings once they didn't have to ride them. I switched to some 170 cranks and really thought I was climbing easier
I went back to my previous size on my guru and no difference.
I think sometimes you get a mental benefit with new parts on your bike
It puts you in a good mood etc.
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sawyer
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by sawyer

wingguy wrote:
sawyer wrote:Shorter cranks can mean the saddle has to be raised however which isn't a good thing

What makes you say that?


To keep the overall leg extension the same. I appreciate however (back to the individual physiology and adaption point) that won't be the case for everyone.
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PhilippCX
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by PhilippCX

cyclespeed wrote:To those saying crank length makes no difference, if you were forced to ride on 140mm or 200mm cranks would you be comfortable with that?


In fact, that's what science seems to suggest. Phil Burt quotes some exhaustive study in his book Bike Fitting which has shown that in a surprisingly large range the crank length makes no difference (after some acclimatization at least).

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cyclespeed
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by cyclespeed

PhilippCX wrote:
cyclespeed wrote:To those saying crank length makes no difference, if you were forced to ride on 140mm or 200mm cranks would you be comfortable with that?


In fact, that's what science seems to suggest. Phil Burt quotes some exhaustive study in his book Bike Fitting which has shown that in a surprisingly large range the crank length makes no difference (after some acclimatization at least).


Fair enough if the jury is out on pedalling efficiency, but I would say that some benefits of shorter cranks are undeniable, namely;

a) better ground clearance - (useful in tight crit races)

b) less leg compression meaning torso lower = more aero (assuming you have the flexibility).

PhilippCX
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by PhilippCX

Totally agree with you on that.

Twisty
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by Twisty

The way i think about it is that assuming one is pushing down on the pedals with about the same force then shorter crank result in pulling the chain faster (due to higher cadence) but at a lower tension so delivering around about the samepower to the wheel.

Overall efficiency has so many variables, shorter cranks means lifting legs up and down through shorter distance (less work) but higher cadence means more work lifting legs up and down at higher frequency. Higher cadence generally works cardio more, lower cadence pushes muscles more, [good evidence for this is when Armstrong was doping on mostly cardio based stuff his cadence increased quite a lot!)

sawyer
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by sawyer

cyclespeed wrote:
PhilippCX wrote:
cyclespeed wrote:To those saying crank length makes no difference, if you were forced to ride on 140mm or 200mm cranks would you be comfortable with that?


In fact, that's what science seems to suggest. Phil Burt quotes some exhaustive study in his book Bike Fitting which has shown that in a surprisingly large range the crank length makes no difference (after some acclimatization at least).


Fair enough if the jury is out on pedalling efficiency, but I would say that some benefits of shorter cranks are undeniable, namely;

a) better ground clearance - (useful in tight crit races)

b) less leg compression meaning torso lower = more aero (assuming you have the flexibility).


I agree cyclespeed, though OTOH, and with 2.5mm move there is little adaptation / benefit / downside, but with a larger move there is the cost of adaptation and quite possibly higher saddle / CoG to factor in. Unless you need the ground clearance there is a good argument it's not really worth it, or very marginal
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sawyer
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by sawyer

Twisty wrote:The way i think about it is that assuming one is pushing down on the pedals with about the same force then shorter crank result in pulling the chain faster (due to higher cadence) but at a lower tension so delivering around about the samepower to the wheel.

Overall efficiency has so many variables, shorter cranks means lifting legs up and down through shorter distance (less work) but higher cadence means more work lifting legs up and down at higher frequency. Higher cadence generally works cardio more, lower cadence pushes muscles more, [good evidence for this is when Armstrong was doping on mostly cardio based stuff his cadence increased quite a lot!)


I'm assuming cadence is unchanged - i.e. on average the shorter crank is offset by a gearing change
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cyclespeed
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by cyclespeed

sawyer wrote:
cyclespeed wrote:
PhilippCX wrote:
cyclespeed wrote:To those saying crank length makes no difference, if you were forced to ride on 140mm or 200mm cranks would you be comfortable with that?


In fact, that's what science seems to suggest. Phil Burt quotes some exhaustive study in his book Bike Fitting which has shown that in a surprisingly large range the crank length makes no difference (after some acclimatization at least).


Fair enough if the jury is out on pedalling efficiency, but I would say that some benefits of shorter cranks are undeniable, namely;

a) better ground clearance - (useful in tight crit races)

b) less leg compression meaning torso lower = more aero (assuming you have the flexibility).


I agree cyclespeed, though OTOH, and with 2.5mm move there is little adaptation / benefit / downside, but with a larger move there is the cost of adaptation and quite possibly higher saddle / CoG to factor in. Unless you need the ground clearance there is a good argument it's not really worth it, or very marginal


It's debatable if your CoG would move higher as although you ass is up a bit, your torso should have come down a bit, so roughly equal.

If I get the time I'll work out how much extra lean angle a 5mm shorter crank will get you before ground strike. At a guess, I would reckon at least a few degrees.

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