Log in:  

Register

The importance of crank length to the cyclist.

01 May 2012 12:41

Martin318is wrote:Personally, I'd go a step further and go to an experienced bike fitter and have them do an assessment and any adjustments for you. Unless you are trying something dramatic, you should be able to make most of the changes on the one day - if done correctly. Changing Q Factor is theoretically a minor change but it depends what your starting point is. In my own case, my position had seemed fine but on inspection I was already irritating the ITB. Any movement of my feet closer together would have made this worse.


Thanks! The good news is my position has already been dialed in by an experienced fitter, with some minor tweeks made once I adapted, so I have a pretty decent baseline.
JimmyFingers wrote:Look I no way dispute Wiggins ... he is doping, he's at it all the time, and has been for years.
User avatar Ripper
Senior Member
 
Posts: 2,493
Joined: 14 Sep 2009 03:41
Location: It's a surprise!

01 May 2012 14:54

coapman wrote:why is there no significant improvement in performance when longer cranks are used.


You seem to be confused - performance clearly IS impaired when your cranks are too short (or too long). It is just that:

1) "too short" (or "too long") are well outside the range of what any experienced cyclist would consider normal, and

2) the reasons for the impairment have nothing to do with the mechanical leverage of the bicycle itself.
acoggan
Junior Member
 
Posts: 1,841
Joined: 18 Mar 2009 11:33

01 May 2012 15:19

acoggan wrote:From the Project 96 tests I mentioned previously:

Image

(Funny, I never noticed before that the figure was mis-labeled! Obviously the top line corresponds to the highest speed, not the lowest speed, and vice-versa.)

Wouldn't it be nice if we actually had all the details that led to this graph so it could be discussed. Just where is this study (my attempts to find it on google seem to fail)? What does "spacing" mean? What bike was tested? How on earth did they achieve spacing of 5 cm on a bike that could actually be ridden? What position was the rider in? Where was "spacing" measured?

Anyhow, let's assume you are correct, drag increases as the legs get wider and wider and wider. What is the mechanism that explains this phenomenon (after all, frontal area doesn't change)? And, how do you explain my findings in the wind tunnel, where drag remained essentially constant despite a "flatter back" and smaller overall frontal area as one shortened the cranks?
Life is short, both reading my posts and training with PowerCranks will make it seem longer
FrankDay
Senior Member
 
Posts: 3,171
Joined: 23 Sep 2010 16:30
Location: N. California

01 May 2012 17:23

acoggan wrote:You seem to be confused - performance clearly IS impaired when your cranks are too short (or too long). It is just that:

1) "too short" (or "too long") are well outside the range of what any experienced cyclist would consider normal, and

2) the reasons for the impairment have nothing to do with the mechanical leverage of the bicycle itself.

1. Actually, performance (power) is affected by crank length as shown by Martin. Within a certain range this affect seems small but if one is truly interested in optimizing performance one should take this into account.

2. And, crank length also affects positioning on the bicycle which can affect both aerodynamics and comfort. Again, if one is truly interested in optimizing performance one needs to consider this affect also.

3. 1 and 2 can interact with each other making the determination of optimum even more difficult.

4. The fact that these issues remain unresolved after over 1300 posts (and close to 75,000 views) suggests it has not been well studied and that there is quite a bit of interest in this issue because it is evident that this area presents, at least, the potential for improvement over the status quo.

5. This thread would be much better served if you actually entered the discussion rather than seeming bent on making pronouncements on how stupid I am for even asking the question.
Life is short, both reading my posts and training with PowerCranks will make it seem longer
FrankDay
Senior Member
 
Posts: 3,171
Joined: 23 Sep 2010 16:30
Location: N. California

01 May 2012 17:50

acoggan wrote:You seem to be confused - performance clearly IS impaired when your cranks are too short (or too long). It is just that:

1) "too short" (or "too long") are well outside the range of what any experienced cyclist would consider normal, and

2) the reasons for the impairment have nothing to do with the mechanical leverage of the bicycle itself.




I am referring to cranks in the 145 to 195 range.
coapman
Junior Member
 
Posts: 755
Joined: 10 Mar 2009 22:02

01 May 2012 18:09

CoachFergie wrote:
Two year old's I have taught to ride a bike have a better instinct for pedalling than you do! And (to keep things on topic) they have the disadvantage of excessively long cranks relative to their leg lengths.




What would you say to a seven year old who after looking at a pedaling torque graph came to you and asked, Why after over 120 years of research can we still not apply any torque when the pedal is at the top (12 o'c) ?
As for that disadvantage, Frank's shorts PC cranks could give them a double advantage, suitable cranks and an opportunity to learn the objectives of circular pedaling.
coapman
Junior Member
 
Posts: 755
Joined: 10 Mar 2009 22:02

01 May 2012 19:25

FrankDay wrote:1. Actually, performance (power) is affected by crank length as shown by Martin. Within a certain range this affect seems small but if one is truly interested in optimizing performance one should take this into account.

2. And, crank length also affects positioning on the bicycle which can affect both aerodynamics and comfort. Again, if one is truly interested in optimizing performance one needs to consider this affect also.

3. 1 and 2 can interact with each other making the determination of optimum even more difficult.

4. The fact that these issues remain unresolved after over 1300 posts (and close to 75,000 views) suggests it has not been well studied and that there is quite a bit of interest in this issue because it is evident that this area presents, at least, the potential for improvement over the status quo.

5. This thread would be much better served if you actually entered the discussion rather than seeming bent on making pronouncements on how stupid I am for even asking the question.


Nice side step of all the data and effect size of ANY of theoretical benefits to changing crank length. Some people never learn or it just doesn't fit their marketing plan.
Hamish Ferguson
coachfergblog.blogspot.co.nz

Smart enough to know a power meter measures power, doesn't improve it :cool:
User avatar CoachFergie
Senior Member
 
Posts: 2,477
Joined: 21 Apr 2009 21:36
Location: Christchurch, New Zealand

01 May 2012 20:37

coapman wrote:What would you say to a seven year old who after looking at a pedaling torque graph came to you and asked, Why after over 120 years of research can we still not apply any torque when the pedal is at the top (12 o'c) ?


Because being really good at applying force to a bicycle pedal when it is as 12 o'clock does not provide you a reproductive advantage.
acoggan
Junior Member
 
Posts: 1,841
Joined: 18 Mar 2009 11:33

01 May 2012 20:40

FrankDay wrote:Wouldn't it be nice if we actually had all the details that led to this graph


It would, wouldn't it? :D

FrankDay wrote:Anyhow, let's assume you are correct, drag increases as the legs get wider and wider and wider.


Not an assumption: fact.

FrankDay wrote:What is the mechanism that explains this phenomenon (after all, frontal area doesn't change)?


The likely answer to that question can be found by reading wind tunnel studies of flow around cylinders (both singly and in pairs).

FrankDay wrote:And, how do you explain my findings in the wind tunnel, where drag remained essentially constant despite a "flatter back" and smaller overall frontal area as one shortened the cranks?


Your anecdotes don't concern me.
acoggan
Junior Member
 
Posts: 1,841
Joined: 18 Mar 2009 11:33

01 May 2012 21:35

acoggan wrote:The likely answer to that question can be found by reading wind tunnel studies of flow around cylinders (both singly and in pairs).
Ah yes. That was exactly the point of Len Brownlie when we were discussing this issue at the wind-tunnel in explaining our findings at the time. This is what led me to ask the 'Q' question because, if one looks at those studies then one would naturally come to the conclusion that at some point, the cylinders would stop affecting each other and the drag would have to drop. Hence, the question, at what 'Q' does that start to occur? Perhaps you didn't understand what I had written on this before. Or, more likely, you didn't care.
Your anecdotes don't concern me.

Which is why you shouldn't be participating in these threads devoted to some of these anecdotes. Further, if your understanding of the science can't explain all of the observations being made then you shouldn't be here pretending that your understanding is complete and coming here criticizing those of us trying to discuss some of these more "off the wall" things.
Life is short, both reading my posts and training with PowerCranks will make it seem longer
FrankDay
Senior Member
 
Posts: 3,171
Joined: 23 Sep 2010 16:30
Location: N. California

01 May 2012 21:49

FrankDay wrote: "off the wall" things.


I think you mean meaningless. Like Jim Martin suggesting the maximum benefit for only the tallest or shortest of rider changing from 170mm cranks was 0.5% which was 4sec in a 40km TT.

Small change when you consider the benefits of training, diet, recovery etc.

Perhaps Andy may care to share some of the findings from the wind tunnel he has built in his basement:D
Hamish Ferguson
coachfergblog.blogspot.co.nz

Smart enough to know a power meter measures power, doesn't improve it :cool:
User avatar CoachFergie
Senior Member
 
Posts: 2,477
Joined: 21 Apr 2009 21:36
Location: Christchurch, New Zealand

01 May 2012 21:57

FrankDay wrote:Ah yes. That was exactly the point of Len Brownlie when we were discussing this issue at the wind-tunnel in explaining our findings at the time. This is what led me to ask the 'Q' question because, if one looks at those studies then one would naturally come to the conclusion that at some point, the cylinders would stop affecting each other and the drag would have to drop.


You need to re-read those studies (assuming, of course, that you ever read them at all). The flow around paired cylinders is quite complex, depending upon their orientation with respect to each other, such that you can't automatically assume that increasing the distance between them will reduce drag. Moreover, since the bicycle is located between the legs, the *possibility* exists for interactions with it as well (although as the data I posted demonstrate, this does not seem to occur).

(Hmmm...I just remembered that Cervelo has also assessed the effects of reduced pedal stance width on aerodynamic drag, and commissioned Jim Martin to determine the effect on power. While I have not seen the data, clearly they were expecting/pursuing a reduction in drag, not an increase as you have hypothesized.)

FrankDay wrote:Which is why you shouldn't be participating in these threads devoted to some of these anecdotes. Further, if your understanding of the science can't explain all of the observations being made then you shouldn't be here pretending that your understanding is complete and coming here criticizing those of us trying to discuss some of these more "off the wall" things.


Au contraire. If people like me didn't participate in threads you start, the world would be left completely misinformed.

(BTW, you'll note that I never claimed to be able to predict the aerodynamic behavior of a complex object such as a cyclist on a bicycle...only reported what others have repeatedly observed.)
acoggan
Junior Member
 
Posts: 1,841
Joined: 18 Mar 2009 11:33

01 May 2012 22:01

CoachFergie wrote:Perhaps Andy may care to share some of the findings from the wind tunnel he has built in his basement:D


Well, I can tell you that a Simkins Egg brake isn't as aerodynamic as most people seem to believe (apparently due - once again! - to the paired cylinder effect). ;)
acoggan
Junior Member
 
Posts: 1,841
Joined: 18 Mar 2009 11:33

01 May 2012 22:07

acoggan wrote:Well, I can tell you that a Simkins Egg brake isn't as aerodynamic as most people seem to believe (apparently due - once again! - to the paired cylinder effect). ;)


Nice, always good to discuss this with people who have spent more than just one session in a wind tunnel or have got off their backsides and read the wealth of research out there.
Hamish Ferguson
coachfergblog.blogspot.co.nz

Smart enough to know a power meter measures power, doesn't improve it :cool:
User avatar CoachFergie
Senior Member
 
Posts: 2,477
Joined: 21 Apr 2009 21:36
Location: Christchurch, New Zealand

01 May 2012 22:40

acoggan wrote:Because being really good at applying force to a bicycle pedal when it is as 12 o'clock does not provide you a reproductive advantage.




Please explain or could it be you are out of your depth here in the matter of applying constant max torque from 12 to 3.
coapman
Junior Member
 
Posts: 755
Joined: 10 Mar 2009 22:02

01 May 2012 22:53

CoachFergie wrote:Nice, always good to discuss this with people who have spent more than just one session in a wind tunnel or have got off their backsides and read the wealth of research out there.


As a person who has read all this research could you state the most important discovery that has resulted from it, or will you run for cover as you did with every other question I asked.
coapman
Junior Member
 
Posts: 755
Joined: 10 Mar 2009 22:02

01 May 2012 23:20

coapman wrote:As a person who has read all this research could you state the most important discovery that has resulted from it, or will you run for cover as you did with every other question I asked.


Aero is important.

Perhaps if you asked questions that had any relevance to form or fitness people would respond.
Hamish Ferguson
coachfergblog.blogspot.co.nz

Smart enough to know a power meter measures power, doesn't improve it :cool:
User avatar CoachFergie
Senior Member
 
Posts: 2,477
Joined: 21 Apr 2009 21:36
Location: Christchurch, New Zealand

01 May 2012 23:25

coapman wrote:Please explain


I thought my explanation was perfectly clear: the reason that things haven't changed is that, from an evolutionary perspective, humans haven't changed .
acoggan
Junior Member
 
Posts: 1,841
Joined: 18 Mar 2009 11:33

01 May 2012 23:27

CoachFergie wrote:Aero is important.


And, while individual differences clearly exist, general guiding principles (e.g., keep your legs close together) can still be stated, thus saving people from wasting a lot of time chasing uninformed speculations.
acoggan
Junior Member
 
Posts: 1,841
Joined: 18 Mar 2009 11:33

01 May 2012 23:35

acoggan wrote:And, while individual differences clearly exist, general guiding principles (e.g., keep your legs close together) can still be stated, thus saving people from wasting a lot of time chasing uninformed speculations.


Excellent advice. It's why when I go into the tunnel to test individuals I am guided by those general principles and the time is spent working on fine tuning.

It's also why I don't experiment with crank length as the research suggest's it's not worth the time. Especially when there are areas that provide far greater improvement (see reviews from Jeukendrup and Faria).
Hamish Ferguson
coachfergblog.blogspot.co.nz

Smart enough to know a power meter measures power, doesn't improve it :cool:
User avatar CoachFergie
Senior Member
 
Posts: 2,477
Joined: 21 Apr 2009 21:36
Location: Christchurch, New Zealand

PreviousNext

Return to General

Who is online

Users browsing this forum: No registered users and 0 guests

Back to top