The importance of crank length to the cyclist. - Page 115 - CyclingNews Forum

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  #1141  
Old 04-10-12, 00:27
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CoachFergie CoachFergie is offline
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Coach Fergie - Unfortunately I cannot understand your retinence to engage Frank on a more intellectual and academic level. I see the discussions between sciguy and others with Frank and for the most part they seem very reasonable and informative. However, you don't participate at the same level, whether by choice or inability, and prefer to resort to negative and unsubstantiated comments, such as manipulating data.
You seem to be under the illusion that Frank is conducting a scientific experiment. All he is doing is generating whatever data he feels will help market his short cranks.

Yes I have spent considerable time in the wind tunnel looking at rider position and aerodynamics but the data is all subject to confidentiality agreements (ie I didn't pay for it) and heading in the academic direction alongside my coaching would love nothing more to get the data published.

What I can say is that it is very easy to manipulate variables in the tunnel to achieve the results you desire. Whether this will have an effect on performance is another matter which is why bike positioning is a several stage process.

Power delivery and efficiency are pretty clear cut (thanks to the work of Martin et al) and in terms of aerodynamics there are many ways for riders to achieve a low profile position where they can look forward, deliver power and maintain the position for race duration.

These improvements don't involve changing crank length which necessitates increasing and pushing the seat back and then having to lift the handlebars and pulling them back as well.
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  #1142  
Old 04-10-12, 00:59
FrankDay FrankDay is offline
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OK, I'm pretty sure where everyone is coming from now.

Frank - I understand the desire to satisfy your own intellectual curiosity and use this forum as a think tank to throw around ideas. I also understand the difficulties in getting a project, whether it be a pilot study or a research project, funded and completed. However, I am a little frustrated because I can see no resolution in sight.
Wow, you really expect there might ever be some resolution in an internet forum? Unbridled optimist you are. :-) The most I think anyone can hope for is to engage in the debate and come to their own conclusion and ignore those who seem to just be in it for other reasons. Anyhow, I hope you come back when we actually have some data to discuss.
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  #1143  
Old 04-10-12, 05:41
sciguy sciguy is offline
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Here is another way to think of what shorter cranks do to the frontal area. The total frontal area of each leg varies with crank position. But, because we are dealing with a reciprocal/rotary motion we can look at the mean or average value for analysis. The mean/average would be when the legs are at 3 and 9 o'clock. Well, when they are in this position the feet are at the same horizontal height compared to the BB regardless of the crank length but the rear end is still pushed up more into the wind shadow of the torso as will the be the upper legs when changing to shorter cranks and keeping fit the same at BDC. In other words, the feet are the same but less leg is exposed to the wind. If we define frontal area as the area directly exposed to the wind and if we start with a typical rider bike fit, the only way the total frontal area can go with this change is down.
Frank,

Interesting that you brought up the mean position argument as it actually works against your intuitive musings. In the mean position each leg is extended farther from the body than with longer cranks. Referencing the bottom bracket is a red herring in this case. It's how extended from the body that is relevant to the aerodynamics. I will say it one more time, increasing hip angle increases exposed leg if back position is maintained.

YMMV,

Hugh
  #1144  
Old 04-10-12, 08:36
sciguy sciguy is offline
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Frank,

One possibly important aspect of this discussion that the wind tunnel will completely miss is the negative influence of the wind gradient on the higher perched rider using the shorter cranks. There is a rapid increase in wind velocity as a body moves from adjacent to the earth where the velocity is zero to higher elevations where it increase very rapidly in the first meter and a half. As we all know, the positive influence of a tail wind never makes up for negative impact head winds when traveling equal distance. The wind tunnel will not "see" this effect since within the tunnel air velocity will be held very constant. As a result we will miss out on how much "aero harm" is caused by lifting the who rider complex higher into a significantly faster moving airstream.



So how are we controlling for this in the wind tunnel?

YMMV,

Hugh
  #1145  
Old 04-10-12, 13:18
FrankDay FrankDay is offline
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Originally Posted by sciguy View Post
Frank,

One possibly important aspect of this discussion that the wind tunnel will completely miss is the negative influence of the wind gradient on the higher perched rider using the shorter cranks. There is a rapid increase in wind velocity as a body moves from adjacent to the earth where the velocity is zero to higher elevations where it increase very rapidly in the first meter and a half. As we all know, the positive influence of a tail wind never makes up for negative impact head winds when traveling equal distance. The wind tunnel will not "see" this effect since within the tunnel air velocity will be held very constant. As a result we will miss out on how much "aero harm" is caused by lifting the who rider complex higher into a significantly faster moving airstream.



So how are we controlling for this in the wind tunnel?

YMMV,

Hugh
It is not necessary to control for this effect in the wind tunnel for several reasons.

1. Wind shear only comes into play when air is moving over the ground. There is no wind shear when self generating wind because of bicycle speed in calm air. Wind speed in this condition is the same at all heights so the wind tunnel effectively reproduces that condition. Wind tunnels try to eliminate wind shear by design to effectively reproduce the conditions of riding in still air. Even if they didn't the major part of the drag is occurring 4 feet off the ground. While your concern is a valid one if one wants to examine the effects of environmental wind on the rider, it is not if one is looking at the effect of bicycle speed in still air on drag. Wind tunnel testing is the gold standard for aerodynamic drag testing because wind tunnel's are designed to reproduce real world conditions and conditions can be so controlled and reproducible. While not perfect, wind tunnel testing has evolved to be generally accepted as valid. If it is good enough for the bicycle manufacturers and the pros it is good enough for me.

2. When doing testing one has to pick certain conditions and then stick with it, trying to change only the one variable being looked at. We have chosen the calm air condition as replicated by the wind-tunnel. The wind shear issue you worry about would be different for every different wind speed and direction. Exactly which one would you choose to test? How would we apply your test results to the calm air condition?

3. the rider is not moved higher off the ground as far as the wind is concerned if the handlebars are not moved and the BB not moved, the conditions of my test. Yes, certain parts of the body are moved further off the ground but they are in or move into the wind shadow of the fixed parts of the body so the effect you are concerned about is minimized and is, in fact, the exact effect we are trying to measure.

4. If you are concerned about this in the real world I recommend that you not look where you are going when riding into a headwind. Raising the head to look forward raises the head higher off the ground and into stronger head winds.

5. No test is perfect. We can only do what we can do. If you can think of a better way of testing this concept I welcome you to go for it then report back. Otherwise, I will be gathering this data for us all, as best I can, to use or ignore or discuss as each of us sees fit.
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  #1146  
Old 04-10-12, 14:28
sciguy sciguy is offline
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Well it's a good thing that bicyclists never ride in the wind


Hugh

Last edited by sciguy; 04-19-12 at 12:56.
  #1147  
Old 04-10-12, 15:10
FrankDay FrankDay is offline
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Originally Posted by sciguy View Post
Well it's a good thing that bicyclists never ride in the wind

I think we're likely to find a good deal of what wind tunnels told us about bicycles turned on its head once Andy Froncioni's brilliant adaptation of "Chung on a stick" becomes available to the general public. Coupled with a power meter the masses will have access to data that really will improve performance at a reasonable cost.

Hugh
Well, there is no single test that will be valid for all aerodynamic conditions. Even the chung test is imperfect because the specific conditions of any single test can never be replicated and the wind shear problem you bring up is a problem for that method also since wind shear conditions depend upon wind speed, which is not only never the same or from the same direction in any ride but will vary from second to second. At least wind tunnel conditions apply to the indoor track, except for when on the curves when the wind speed at the head is lower than the wind speed at the ground, the exact opposite of the "normal" wind shear problem.

This is an issue with any study. To study the effects of one variable all other variables must be held constant. For this type of analysis currently the wind tunnel is the gold standard even though the exact combination of variables may not be exactly what you would have chosen. Further, if a researcher doesn't use a method similar to what has been done before then it is hard to compare results.

And, elapid was lobbying for you to design this "study" yet, it seems, you don't understand this very basic limitation of any study, let alone the specific aerodynamic issues that we are trying to test. What you don't seem to understand is any study design can be criticized since it is not possible to design a study to account for every condition. Do it your way and it doesn't accurately reflect quiet conditions.

Hold your concerns until the data is available then you can bring it up as part of the discussion.
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Last edited by FrankDay; 04-10-12 at 15:22.
  #1148  
Old 04-10-12, 15:37
sciguy sciguy is offline
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Originally Posted by FrankDay View Post
Well, there is no single test that will be valid for all aerodynamic conditions. Even the chung test is imperfect because the specific conditions of any single test can never be replicated and the wind shear problem you bring up is a problem for that method also since wind shear conditions depend upon wind speed, which is not only never the same or from the same direction in any ride but will vary from second to second.

Ahhh but the beauty of Alphmantis aka "Chung on a stick" is that it captures real time variation of winds right at the bicycle via a pitot tube like apparatus. No it doesn't do it at all heights but testing is very much more real than in a wind tunnel.

Your statement "Wind tunnel testing is the gold standard for aerodynamic drag testing because wind tunnel's are
designed to reproduce real world conditions" is absolute rubbish. Wind tunnels produce incredibly idealized conditions rather than real world ones. Yes the idealized air currents are nicely repeatable and that is essential for consistency of experimentation but please don't brand them as realistic in nature.



At least wind tunnel conditions apply to the indoor track, except for when on the curves when the wind speed at the head is lower than the wind speed at the ground, the exact opposite of the "normal" wind shear problem.

YMMV,

Hugh
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  #1149  
Old 04-10-12, 16:01
FrankDay FrankDay is offline
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Ahhh but the beauty of Alphmantis aka "Chung on a stick" is that it captures real time variation of winds right at the bicycle via a pitot tube like apparatus. No it doesn't do it at all heights but testing is very much more real than in a wind tunnel.
The chung method simply gives one an average drag for a particular ride. Because conditions cannot be controlled or replicated it will not be a particularly good method for use in studies despite the fact that it will be quite useful for the individual athlete.
Quote:
Your statement "Wind tunnel testing is the gold standard for aerodynamic drag testing because wind tunnel's are designed to reproduce real world conditions" is absolute rubbish. Wind tunnels produce incredibly idealized conditions rather than real world ones. Yes the idealized air currents are nicely repeatable and that is essential for consistency of experimentation but please don't brand them as realistic in nature.
Wind tunnels are the gold standard for evaluating aerodynamic drag exactly because they produce idealized, reproducible, conditions. Without that it would be much more difficult to compare one run to another. And, those idealized conditions they create happen to be close to real world, still air, conditions. wind tunnels are designed for a wide variety of needs (wind tunnels even exist to reproduce the conditions of spacecraft reentry using modeling techniques). Low speed wind tunnels are quite useful for evaluating aerodynamic drag in bicycles in quiet air very well.

Anyhow, that is what I am doing. As I said, if you think it can be done better then you are welcome to repeat the study using your own protocol and let everyone know your methods and results. BTW, it is my prediction that the aerodynamic benefits of short cranks will be even greater in headwind/windshear conditions, because more frontal area is being put in the wind shadow up high, where wind speed is greatest, and the head is lowered somewhat, where wind speed would be less.

Of course, there is another method available to do this analysis, computer modeling and analysis. But, that is not what I will be doing. Enjoy.
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Last edited by FrankDay; 04-10-12 at 16:22.
  #1150  
Old 04-10-12, 20:42
coapman coapman is offline
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Power delivery and efficiency are pretty clear cut (thanks to the work of Martin et al)

.


Please explain, and if you are wrong here, you could also be wrong in the matter of aerodynamic position for best power delivery.
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