Crank Length

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BRM
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by BRM

cyclespeed wrote:I know it's been discussed a lot, but there still seems to be little agreement on the 'best' crank length (for a given height).
There are more parameters than only height. Like upper and lower leg ratios, size of foot, angle of foot and other ratios. Power of a person, conditions to ride under, personal preference etc etc.


What I find most interesting is that many out there say that a longer crank gives you more leverage, and therefore must be better. But it's the same extra leverage as changing down a gear, so their point is invalid.
Eh what is longer cranks anyway? without good reference its hollow information. The diameter of circle your feet describe is another factor you left out.


I find I climb best by maintaining a high (100ish) cadence, and smaller cranks help with that.
Again no reference, no information about your sizes and other important facts and no sign of what you understand as smaller crancks. Besides that, your single individual experience can't be a reference for general advice.


I think that one person is more sensitive than the other for cranck lenghts.
I also think that you need to see that the optimal crank lenght is for each individual different. There is no black and white format.

Till now I have read nothing new in this topic. . . . .

wingguy
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by wingguy

sawyer wrote:
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.

No shit sherlock :lol:

I meant why isn't it a good thing?

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cyclespeed
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by cyclespeed

Just for kicks, using dimensions from my 52 Sworks Tarmac, (ground to axle = 270mm, crank width = 134mm), by my calcs,

a 175mm would strike at 54.8'
and
a 170mm would strike at 56.3',

so about a 1.5' gain.

(I've ignored pedals, which would of course strike sooner).

sawyer
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by sawyer

wingguy wrote:
sawyer wrote:
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.

No shit sherlock :lol:

I meant why isn't it a good thing?


Because it raises the CofG

I know we all know this, but it's striking how many less obsessed roadies don't get how important saddle height, tilt and fore-aft is to correct fit, comfort and handling
----------------------------------------
Stiff, Light, Aero - Pick Three!! :thumbup:

sawyer
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by sawyer

cyclespeed wrote:
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.


Hmm ... your torso would only really come down if the bars were dropped. that might be possible with a shorter crank

I find saddle height has a big effect on the feeling of where the CofG is in any case. Even a small change can be really noticeable at speed downhill
----------------------------------------
Stiff, Light, Aero - Pick Three!! :thumbup:

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cyclespeed
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by cyclespeed

BRM wrote:
cyclespeed wrote:I know it's been discussed a lot, but there still seems to be little agreement on the 'best' crank length (for a given height).
There are more parameters than only height. Like upper and lower leg ratios, size of foot, angle of foot and other ratios. Power of a person, conditions to ride under, personal preference etc etc.


What I find most interesting is that many out there say that a longer crank gives you more leverage, and therefore must be better. But it's the same extra leverage as changing down a gear, so their point is invalid.
Eh what is longer cranks anyway? without good reference its hollow information. The diameter of circle your feet describe is another factor you left out.


I find I climb best by maintaining a high (100ish) cadence, and smaller cranks help with that.
Again no reference, no information about your sizes and other important facts and no sign of what you understand as smaller crancks. Besides that, your single individual experience can't be a reference for general advice.



I think that one person is more sensitive than the other for cranck lenghts.
I also think that you need to see that the optimal crank lenght is for each individual different. There is no black and white format.

Till now I have read nothing new in this topic. . . . .


I would agree that your morphology (length of femur, size of foot, etc. etc.) is important in deciding your crank length. This much is obvious. Afterwards power, conditions and preference are more hazy. But if a 'classic' measurement pops out 177.5mm, then presumably it may be worth trying as much as 10mm either side of this to see what effect it has.

'Longer' in this context just means longer. i.e. a 180mm crank gives more 'leverage' than a 170mm one. Well yes, but a 28 tooth gear on the back gives more leverage than a 25 too.

If you want my info, well 1.75m tall, shortish legs, was on 172.5mm, tried 175mm, hated it. Went to 170mm, much better, easier to spin, no loss of performance. More aero. I'm happy spinning or stomping, but prefer the former. For sure, my experience may not work for everybody, but I can't change that!

It seems that over the last few years, shorter cranks (i.e. dropping down a size or two from what you normally use) are becoming more popular. Be it anecdotally from pro teams, or from the TT / tri scene, it all seems to point in that direction. If that's not new, then I apologize.....

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cyclespeed
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by cyclespeed

sawyer wrote:Hmm ... your torso would only really come down if the bars were dropped. that might be possible with a shorter crank


Yes, after fitting 170's I've been progressively lowering the front. It's now no spacers on a 130mm stem with a 120mm (short) headtube. (Sworks Tarmac 52).

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by RyanH

Wouldn't a 1cm change in crank length be similar to a 1cm change in BB drop? Lower is more stable (175), higher is more responsive but twitchier (165).

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wingguy
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by wingguy

sawyer wrote:Because it raises the CofG

Does it, though?

If you follow through the thinking if you were taking full advantage of crank length possibilities, going to a 5mm shorter crank would mean you raise the saddle 5mm, but could run the bars 1cm lower without decreasing the hip angle. Assuming the rest of the fit allows for that, obviously.

Where does that put the CofG? Pretty tough to say for sure, but I'm not sure you can say it would be definitely higher.

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cyclespeed
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by cyclespeed

RyanH wrote:Wouldn't a 1cm change in crank length be similar to a 1cm change in BB drop? Lower is more stable (175), higher is more responsive but twitchier (165).

Sent from my SM-G930V using Tapatalk


No.

If you had 175mm cranks and you could move your BB down 10mm, then the top crank would be like a 165mm and the bottom a 185mm.

Not the same thing.

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BRM
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by BRM

cyclespeed wrote:
BRM wrote:
cyclespeed wrote:I know it's been discussed a lot, but there still seems to be little agreement on the 'best' crank length (for a given height).
There are more parameters than only height. Like upper and lower leg ratios, size of foot, angle of foot and other ratios. Power of a person, conditions to ride under, personal preference etc etc.


What I find most interesting is that many out there say that a longer crank gives you more leverage, and therefore must be better. But it's the same extra leverage as changing down a gear, so their point is invalid.
Eh what is longer cranks anyway? without good reference its hollow information. The diameter of circle your feet describe is another factor you left out.


I find I climb best by maintaining a high (100ish) cadence, and smaller cranks help with that.
Again no reference, no information about your sizes and other important facts and no sign of what you understand as smaller crancks. Besides that, your single individual experience can't be a reference for general advice.



I think that one person is more sensitive than the other for cranck lenghts.
I also think that you need to see that the optimal crank lenght is for each individual different. There is no black and white format.

Till now I have read nothing new in this topic. . . . .


I would agree that your morphology (length of femur, size of foot, etc. etc.) is important in deciding your crank length. This much is obvious. Afterwards power, conditions and preference are more hazy. But if a 'classic' measurement pops out 177.5mm, then presumably it may be worth trying as much as 10mm either side of this to see what effect it has.
When its Obvious for you why refering to lenght only? Because thats what you did. Power, conditions(like flat or hilly) and preferences are not hazy at all. Don't think too black and white. People fall in between some figures for optimal cranklenght. Its possible that you fall in the middle of the range but also at the start or the end of this particular range. Which makes a difference for the best way to go . . .

'Longer' in this context just means longer. i.e. a 180mm crank gives more 'leverage' than a 170mm one. Well yes, but a 28 tooth gear on the back gives more leverage than a 25 too. Longer means nothing when you describe no single data as reference/startiongpoint. That is what I mean. You started a topic with a sumup of so called facts but are not aware that you need to be consequent and strict when you want to hold on to facts.

If you want my info, well 1.75m tall, shortish legs, was on 172.5mm, tried 175mm, hated it. Went to 170mm, much better, easier to spin, no loss of performance. More aero. I'm happy spinning or stomping, but prefer the former. For sure, my experience may not work for everybody, but I can't change that!
No I dont need your data, the point is that your personal experience is not ruling and again when you try to make the discussion general you have here an invalid argument. Don't mix general things with individual experience, it leads away of clarity.


It seems that over the last few years, shorter cranks (i.e. dropping down a size or two from what you normally use) are becoming more popular. Be it anecdotally from pro teams, or from the TT / tri scene, it all seems to point in that direction. If that's not new, then I apologize.....
Imo opinion, the majority of people buy a complete bike and don't think about changing or experimenting with crancks at all.
The (niche) discussion about crank lenghts is already decennia going on. Some years ago triggered a bit extra by the TT world
.

Of course I have nothing against such a discussion because road racing is about optimizing. But many optimazation discussions are flawed and out of proportion. So tell me what do you exactlywant to achieve with starting this topic?

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cyclespeed
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by cyclespeed

BRM wrote:
I would agree that your morphology (length of femur, size of foot, etc. etc.) is important in deciding your crank length. This much is obvious. Afterwards power, conditions and preference are more hazy. But if a 'classic' measurement pops out 177.5mm, then presumably it may be worth trying as much as 10mm either side of this to see what effect it has.
When its Obvious for you why refering to lenght only? Because thats what you did. Power, conditions(like flat or hilly) and preferences are not hazy at all. Don't think too black and white. People fall in between some figures for optimal cranklenght. Its possible that you fall in the middle of the range but also at the start or the end of this particular range. Which makes a difference for the best way to go . . .
I'm saying that by inputting your height inseam, femur, etc. many calculators, bikefitters, will pop out a crank length for you. Quite easy. Saying, I make 330W and like hills is less easy to choose your crank length. See what I mean?

'Longer' in this context just means longer. i.e. a 180mm crank gives more 'leverage' than a 170mm one. Well yes, but a 28 tooth gear on the back gives more leverage than a 25 too. Longer means nothing when you describe no single data as reference/startiongpoint. That is what I mean. You started a topic with a sumup of so called facts but are not aware that you need to be consequent and strict when you want to hold on to facts.
I have 2 pieces of string. One is longer than the other. I can tie more knots in the long piece. I don't have to say how long in cm they are. I'm wondering, is English your mother tongue? (honest question).

If you want my info, well 1.75m tall, shortish legs, was on 172.5mm, tried 175mm, hated it. Went to 170mm, much better, easier to spin, no loss of performance. More aero. I'm happy spinning or stomping, but prefer the former. For sure, my experience may not work for everybody, but I can't change that!
No I dont need your data, the point is that your personal experience is not ruling and again when you try to make the discussion general you have here an invalid argument. Don't mix general things with individual experience, it leads away of clarity.



My personal experience is what it is. Make of it what you will. Ignore it if you prefer, your choice. Personally, I find other rider's experiences interesting and can often learn by the mistakes and successes of others. Describing what works for me does not invalidate some of the points we have been discussing.


It seems that over the last few years, shorter cranks (i.e. dropping down a size or two from what you normally use) are becoming more popular. Be it anecdotally from pro teams, or from the TT / tri scene, it all seems to point in that direction. If that's not new, then I apologize.....
Imo opinion, the majority of people buy a complete bike and don't think about changing or experimenting with crancks at all.
The (niche) discussion about crank lenghts is already decennia going on. Some years ago triggered a bit extra by the TT world
.
I agree it's old, but I have noticed a shift in the last few years towards shorter cranks and more interest in this idea.

Of course I have nothing against such a discussion because road racing is about optimizing. But many optimazation discussions are flawed and out of proportion. So tell me what do you exactlywant to achieve with starting this topic?
[/quote]

It's a forum discussion board, so I thought I'd discuss and hear what others thought on the subject. Is that OK?

wingguy
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by wingguy

sawyer wrote:I find saddle height has a big effect on the feeling of where the CofG is in any case. Even a small change can be really noticeable at speed downhill

Are you sure that has to do with CofG and not things like leg extension, balance, the ability to lean the bike under you and weight the outer pedal through the corner?

Because if the height of your centre mass is that important how do you explain the ability of taller riders to ride bikes?

What I mean is, I'm 5'8". So if changing my crank length by 2.5 or 5mm and raising the saddle accordingly would have a noticeable effect on my downhill handling then surely someone like Peter Sagan (who is 6'0" and has both his bars and saddle several centimetres higher than me) should be like Bambi on ice by comparison when it came to going around a corner... but obviously the opposite is true. He's way better than me and better even than almost any other professional racer, whether they are higher or lower on their bikes. So what gives? :noidea:

Twisty
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by Twisty

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


Yes E.g. changing from 175mm->165mm cranks you lose 6% leverage which you can claw back by changing from 15T->16T at the rear. If you keep pedalling cadence the same then the obvious fly in the ointment is that you will be going 6% slower. I suspect most people would natrually increase their cadence a bit, after all their feet would be travelling 6% less distance per revolution.

Are you sure that has to do with CofG and not things like leg extension, balance, the ability to lean the bike under you and weight the outer pedal through the corner?

Because if the height of your centre mass is that important how do you explain the ability of taller riders to ride bikes?

What I mean is, I'm 5'8". So if changing my crank length by 2.5 or 5mm and raising the saddle accordingly would have a noticeable effect on my downhill handling then surely someone like Peter Sagan (who is 6'0 both his bars and saddle several centimetres higher than me) should be like Bambi on ice by comparison when it came to going around a corner... but obviously the opposite is true. He's way better than me and better even than almost any other professional racer, whether they are higher or lower on their bikes. So what gives?


Yeah but the pros both tall and short all have super low c.o.g compared to amateurs because they have a lot of weight in their muscular legs and lean midriffs. This is why MAMILs are such a hazard in sportives, their relatively weak/light legs and flabby/massive midriffs gives them a dangerously high c.o.g. it is suprising that they can corner at all.
Seriously though, i think it is leg extension which is the noticible difference.

Dez33
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by Dez33

mattr wrote: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.


Yes there is. Google J.C. Martin crank length and you will get three or four papers. Basically crank length is not a determinant of maximum power production.

Anything other than those studies is an individual anecdote or theory.

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