Shorter crank experiences. Then back to longer ones!

Discuss light weight issues concerning road bikes & parts.
stormur
Posts: 1182
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Location: FIN

by stormur

I always wondered ( and still do ); how show sole thickness affect crank length ... .

difference between 2 shoe brands can, and possibly will make a change in sole thickness BIGGER THAN 2.5mm . So, from biomechanical point of view all statements about changing crank arm length and feelings about it are worthless, isn't it ?

I didn't noticed anyone reporting "my new shoes have thinner sole, so had to reduce crank arm length to accomodate it" ( or reverse) ....
Apllies also to switch between road/mtb pedals. And personal cleat position ( no one has same, and this affects "crank length" more than 2.5mm .

I'd like to be wrong about it , but I afraid I am not. Correct me if I am.

Edit : did I mention pedal stack ? :mrgreen:
Go to Heaven for the climate, Hell for the company.
Mark Twain


I can be wrong, and have plenty of examples for that ;)

by Weenie


xcnick
Posts: 139
Joined: Fri Jan 21, 2011 5:27 pm

by xcnick

That depends if you're changing your shoes and pedal type regularly! If changing crank length whilst using the same shoes and pedals then the only thing changing is the crank length.

r4nd0mv4r14bl3
Posts: 54
Joined: Thu Jun 11, 2015 9:26 am

by r4nd0mv4r14bl3

stormur wrote:I always wondered ( and still do ); how show sole thickness affect crank length ... .

difference between 2 shoe brands can, and possibly will make a change in sole thickness BIGGER THAN 2.5mm . So, from biomechanical point of view all statements about changing crank arm length and feelings about it are worthless, isn't it ?

I didn't noticed anyone reporting "my new shoes have thinner sole, so had to reduce crank arm length to accomodate it" ( or reverse) ....
Apllies also to switch between road/mtb pedals. And personal cleat position ( no one has same, and this affects "crank length" more than 2.5mm .

I'd like to be wrong about it , but I afraid I am not. Correct me if I am.

Edit : did I mention pedal stack ? :mrgreen:
Crank length changes the size of the circle your foot makes. You cannot correct for this with your saddle height. Pedal stack increase however just moves the entire circle up and you can change your saddle height to adjust for this.

Edit: spelling & clarity

Sent from my SM-N9005 using Tapatalk

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Lelandjt
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Joined: Tue Jan 19, 2016 7:10 am

by Lelandjt

I'm totally happy with the feeling of 175 cranks and experimenting with 165 and 170 on my MTBs has me wure that 175 or 172.5 is the right size for my road bike but....
When I get really low the limitation is my thighs tapping my chest. I could be more comfortable in that low position if they weren't tapping with each pedal stroke or get even lower. Has anyone changed crank length purely because of thigh-chest contact? I already have a longer reach and more forward saddle than "normal" but my saddle-handlebar drop is much greater than normal.

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wheelsONfire
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Location: NorthEU

by wheelsONfire

I was persuaded i should use 175mm cranks instead of 172.5mm.
I took the advice as i didn't want to wait several months for the 172.5mm version.
Once on the 175 version, i noted they felt huge.
I couldn't pedal very well on these.
Felt like to much up and to much down when pedaling.
Tried a buddies 170mm cranks, clearly better than 175, but 172.5mm version seemed best.
However, i have been realizing that 170 version was without doubt better than 175.

I think i could best adapt to the smaller length.
Usually spin around 90 rpm.
Bikes:

Ax Lightness Vial EVO D
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TonyM
Posts: 2003
Joined: Thu Jan 22, 2015 4:11 pm

by TonyM

mattr wrote:Just as another anecdote. I've been running 170s for 33 years and never had the slightest issue with any sort of biomechanical or knee pain.
Got 172.5 when buying a new groupset (3 month wait for 170s).
Almost instant knee pain. Worse on one side. Spent some weeks looking for 170s in stock then spotted some 165s on a local buy and sell page for not much (been delivered on a bike then taken off to put a PM on)

Took one ride to get completely used to them. Everything about them feels better. Can't believe I didn't try them sooner.

Only issue is that I've got 9 more bikes that now need shorter cranks.
That's sounds interesting.
What is your inseam?
What is usual cadence?

AJS914
Posts: 1950
Joined: Tue Jan 28, 2014 6:52 pm

by AJS914

Lelandjt wrote: When I get really low the limitation is my thighs tapping my chest. I could be more comfortable in that low position if they weren't tapping with each pedal stroke or get even lower. Has anyone changed crank length purely because of thigh-chest contact?

The comfort of going from 175 to 170mm is probably the best aspect for me. With 170s I raised my saddle 5mm and left my stem where it was. It felt a lot better.

stormur
Posts: 1182
Joined: Tue Aug 12, 2014 3:50 pm
Location: FIN

by stormur

r4nd0mv4r14bl3 wrote:
stormur wrote:I always wondered ( and still do ); how show sole thickness affect crank length ... .

difference between 2 shoe brands can, and possibly will make a change in sole thickness BIGGER THAN 2.5mm . So, from biomechanical point of view all statements about changing crank arm length and feelings about it are worthless, isn't it ?

I didn't noticed anyone reporting "my new shoes have thinner sole, so had to reduce crank arm length to accomodate it" ( or reverse) ....
Apllies also to switch between road/mtb pedals. And personal cleat position ( no one has same, and this affects "crank length" more than 2.5mm .

I'd like to be wrong about it , but I afraid I am not. Correct me if I am.

Edit : did I mention pedal stack ? :mrgreen:
Crank length changes the size of the circle your foot makes. You cannot correct for this with your saddle height. Pedal stack increase however just moves the entire circle up and you can change your saddle height to adjust for this.

Edit: spelling & clarity

Sent from my SM-N9005 using Tapatalk
Where I did mention saddle height ? oops: no where. because it's Irrelevant. higher pedal stack or thicker sole make circle smaller, lower stack, thinner sole make it bigger. Those factors, if not taken into consideration make all discussion about crank arm length silly, to be kind and gentle. If calling it straightforward it is BS.
Go to Heaven for the climate, Hell for the company.
Mark Twain


I can be wrong, and have plenty of examples for that ;)

Fiery
Posts: 395
Joined: Sat Mar 16, 2013 9:21 am

by Fiery

Stack height doesn't affect the radius of the circle. When cranks are horisontal, changing the stack moves the feet at a right angle in relation to the cranks - no change in radius. When cranks are vertical, changing the stack effectively lengthens one crank and shortens the other by the same amount - zero net change to the radius. Try to draw it if it's still not clear.

stormur
Posts: 1182
Joined: Tue Aug 12, 2014 3:50 pm
Location: FIN

by stormur

when the crank arm AND CLEAT are horisontal AT THE SAME TIME- you're right. But such situation doesn't exist in real life. Then comes also next aspect : center of rotation ;)

1,429% is the difference in length between 175 and 172,5 mm crank arm length. Some want me/you to believe that such difference makes such sensation.... Well ;)
Go to Heaven for the climate, Hell for the company.
Mark Twain


I can be wrong, and have plenty of examples for that ;)

mattr
Posts: 3477
Joined: Fri May 25, 2007 6:43 pm
Location: The Grim North.

by mattr

TonyM wrote:That's sounds interesting.
What is your inseam?
What is usual cadence?
about 81cm inseam, cadence is usually in the 90's. Slower than it used to be, i'm getting old.

mattr
Posts: 3477
Joined: Fri May 25, 2007 6:43 pm
Location: The Grim North.

by mattr

stormur wrote:Where I did mention saddle height ? oops: no where. because it's Irrelevant. higher pedal stack or thicker sole make circle smaller, lower stack, thinner sole make it bigger. Those factors, if not taken into consideration make all discussion about crank arm length silly, to be kind and gentle. If calling it straightforward it is BS.
:lol: Go and draw some circles.
I'd like to be wrong about it , but I afraid I am not. Correct me if I am.
You can correct yourself.

wingguy
Posts: 3743
Joined: Thu Mar 08, 2012 11:43 pm

by wingguy

stormur wrote:I always wondered ( and still do ); how show sole thickness affect crank length ...
It doesn’t, at all. Changing cranks lengths means you are pedalling a bigger or smaller circle. Changing shoe thickness means you are pedalling the same size circle in a different place.

So, this means that changing crank lengths and adjusting the saddle accordingly changes the amount of hip and knee flexion in your pedal stroke. Changing shoe thicknesses and adjusting the saddle does not. (Though the ankle flexion may change, this is a very different effect).
difference between 2 shoe brands can, and possibly will make a change in sole thickness BIGGER THAN 2.5mm . So, from biomechanical point of view all statements about changing crank arm length and feelings about it are worthless, isn't it ?
Following on from the above, this conclusion is absolutely incorrect.

wingguy
Posts: 3743
Joined: Thu Mar 08, 2012 11:43 pm

by wingguy

stormur wrote: 1,429% is the difference in length between 175 and 172,5 mm crank arm length. Some want me/you to believe that such difference makes such sensation.... Well ;)
The difference between 170 and 172.5mm cranks is 5mm. Go change your saddle height by 5mm and I’ll guarantee you notice the difference.

AJS914
Posts: 1950
Joined: Tue Jan 28, 2014 6:52 pm

by AJS914

Depends on whether you are talking radius or diameter and which number you think is more important.

by Weenie


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