The importance of crank length to the cyclist.

[FrankDay]

You're still stuck in this mindset that you change the saddle to pad drop when you change the crank length. You need to separate out the two things. First of all establish your optimal saddle to pad drop that makes you most aero. Then change crank length, moving both saddle and pads by the same amount. This way you isolate the two things you're trying to measure. Once you have your most aero saddle to pad drop there is no reason to increase the drop when you move to shorter cranks because it will only make you less aero. If you can't ride with your optimal saddle to pad drop, then you need to train in that position till you can, it's typically not a particularly extreme position, more people leave the wind tunnel with their drop reduced than leave with it increased, i.e. most people in their quest for lowness actually go lower than is most aero. If you look at the guys in the UK who ride for the drag2zero team, all of whom have wind tunnel optimised positions, they typically do not have extreme positions. And it was one of their guys who mentioned about most people leaving the tunnel having moved up not down.

How does anyone know what the optimal saddle to pad drop is without experimenting. If you will examine our data you will see that drag did not depend upon saddle to pad drop and was pretty much constant over a 10 inch difference as the rider became low. If the upper body and lower body respond differently to the wind then, in a head wind, if we can improve the shape of the upper body, where the wind is the greatest this should more than compensate for the increase seen from the lower body, where the wind is less. You need to get unstuck from your bias and look at the data. Shorter cranks should do relatively better from an aerodynamic perspective in a headwind than they would in still air. And, my guess is the people on the drag2zero team when in the wind tunnel are looking at aerodynamic drag exclusively and not looking at what these changes do to power nor at crank length.

 

[twothirds]

1. Shorter cranks allow you to lower the front end, since the knee moves away from the chest. This would actually lower the highest part of the back.

This is true, although lowering the highest part of the back is not necessarily aerodynamically optimal in each situation. Most people see there best aerodynamics in a position that puts the chest wall parallel to the ground. This still means that the back is somewhat rounded. A lot of drag is generated not just from how an object "rams" into the wind, but how the wind comes off an object. Lowering the chest may increase drag by disrupting airflow. Lower is not always better, and frontal area is not the only determinant of drag.

2. Shorter cranks move the pedal away from the ground which would allow you to design a bike with a lower BB, lowering the entire body all at once.

3. The upper leg has been moved down into lower speed air. As the wind tunnel has shown this presents a problem in still air but is, perhaps, much less a problem, or an advantage, in a strong head wind.

Has lowering the entire body been proven to lower drag? I truly don't know, but I would have to speculate that it doesn't. My opinion being that unless you are getting low enough that you are able to get into the boundary layer of air moving over the ground (where it's slower, albeit this layer is not very thick), than it's not going to make any measurable difference.

Not sure if I understand your logic on this point. A shorter crank means that your legs have a higher average angle of extension. If I'm correct, does your thinking mean that your leg spends more time in a position of higher power output, because I can sort of agree on that. Aerodynamically this would seem seem counter-intuitive to me. Surface friction being the same, the chord length of an object is a large determinant of drag. Longer chord length, usually lower drag. With shorter cranks equaling longer average extension, your leg is presenting less average chord length than a set up with longer cranks which to me would increase drag. A headwind would make a short crank set up worse.

Not trying to rag on your efforts. Just some questions/exchange of ideas.

taras

 

[Boeing]

I just have to interrupt this discussion to give myself props for the comment about high wire unicycle crank arm length. that was awesome.

 

[Martin318is]

the better question is what type of competition would the cranks you posted a picture of make anyone better?


Off the top of my head I'm thinking hi wire unicycle at cirque du soleil or Ringling bros.

and Frank, with no disrespect I am serious here.

Hmmm.. I would imagine that given aerodynamics is meaningless in that context, there would be much more bias towards whether having long cranks helps or hinders balance and control.. I'd guess longer cranks help...

 

[FrankDay]

This is true, although lowering the highest part of the back is not necessarily aerodynamically optimal in each situation. Most people see there best aerodynamics in a position that puts the chest wall parallel to the ground. This still means that the back is somewhat rounded. A lot of drag is generated not just from how an object "rams" into the wind, but how the wind comes off an object. Lowering the chest may increase drag by disrupting airflow. Lower is not always better, and frontal area is not the only determinant of drag.

I can agree that predicting drag is much more complicated than simply knowing frontal area. I think my data proves that. But, your statement "Lowering the chest may increase drag by disrupting airflow." has no more support than this statement: "Lowering the chest may decrease drag by smoothing airflow." My data suggests that if shorter cranks increase drag on the legs overall then the concomitant "lowering" of the chest must reduce drag on the chest since overall drag generally remained constant over a wide range.

Has lowering the entire body been proven to lower drag? I truly don't know, but I would have to speculate that it doesn't. My opinion being that unless you are getting low enough that you are able to get into the boundary layer of air moving over the ground (where it's slower, albeit this layer is not very thick), than it's not going to make any measurable difference.

It is easy to prove using a thought experiment as long as you are talking headwind because of the phenomenon of wind shear. It doesn't matter what the wind speed is 4 feet off the ground, even in a hurricane the wind speed at the ground is zero. Any vertically shaped object moving at a set wind speed at head level will experience lower drag in the head wind because most of the body is seeing a lower wind speed.

Not sure if I understand your logic on this point. A shorter crank means that your legs have a higher average angle of extension. If I'm correct, does your thinking mean that your leg spends more time in a position of higher power output, because I can sort of agree on that. Aerodynamically this would seem seem counter-intuitive to me. Surface friction being the same, the chord length of an object is a large determinant of drag. Longer chord length, usually lower drag. With shorter cranks equaling longer average extension, your leg is presenting less average chord length than a set up with longer cranks which to me would increase drag. A headwind would make a short crank set up worse.

Not if you consider wind shear. Head winds and wind shear present a completely different situation from riding in still air and this situation is not tested in the wind tunnel

 

[sciguy]

The only criticism I would have of your friends approach is he hasn't tested to see if shorter cranks might result in more power. He is particularly cramped and it might be that this doesn't affect his power but unless he tests he cannot know.

Actually he did initially test using a used set of adjustable Power Cranks that be purchased cheaply from Ebay. He locked them out so they acted as fixed cranks and tested lengths from 200mm to 165mm. His found the 175s to be the best compromise in terms of comfort and power and aeroness. So scratch that criticism of the list

Not sure why you've decided that he is cramped. Mike looks to be holding somewhat of a Superman Position in his pictures. From my experience it's way harder to hold that position for 5+ hours than the one my friend rides.
I would not be surprised tested slightly more aero if he took on Mike's postion but can't imagine holding it for 112 miles.

I keep getting the feeling that you yourself have very little real personal experience riding time trial bikes or using power meters.

Hugh

 

[sciguy]

You're still stuck in this mindset that you change the saddle to pad drop when you change the crank length. You need to separate out the two things. First of all establish your optimal saddle to pad drop that makes you most aero. Then change crank length, moving both saddle and pads by the same amount. This way you isolate the two things you're trying to measure. Once you have your most aero saddle to pad drop there is no reason to increase the drop when you move to shorter cranks because it will only make you less aero. If you can't ride with your optimal saddle to pad drop, then you need to train in that position till you can, it's typically not a particularly extreme position, more people leave the wind tunnel with their drop reduced than leave with it increased, i.e. most people in their quest for lowness actually go lower than is most aero. If you look at the guys in the UK who ride for the drag2zero team, all of whom have wind tunnel optimised positions, they typically do not have extreme positions. And it was one of their guys who mentioned about most people leaving the tunnel having moved up not down.

Ding, Ding , Ding !!!!!!!!!!!!!!! We have a winner!!!!!!!!!!!!!!!!!!! You are so on target here. As my scientist wife keeps saying "doesn't Frank realize that by changing crank length, raising the seat but not also raising the arm pads he's changing two variables each time rather than one

Thanks for the excellent post.

Hugh

 

[simo1733]

How does anyone know what the optimal saddle to pad drop is without experimenting. If you will examine our data you will see that drag did not depend upon saddle to pad drop and was pretty much constant over a 10 inch difference as the rider became low. If the upper body and lower body respond differently to the wind then, in a head wind, if we can improve the shape of the upper body, where the wind is the greatest this should more than compensate for the increase seen from the lower body, where the wind is less. You need to get unstuck from your bias and look at the data. Shorter cranks should do relatively better from an aerodynamic perspective in a headwind than they would in still air. And, my guess is the people on the drag2zero team when in the wind tunnel are looking at aerodynamic drag exclusively and not looking at what these changes do to power nor at crank length.[/QUOTE

Drag2Zero aim to make people faster, which of course involves finding the correct compromise between pwer, comfort and drag.At least thats what they say.
I notice that a lot of their clients end up with forearms angled upwards.

 

[Martin318is]

Ding, Ding , Ding !!!!!!!!!!!!!!! We have a winner!!!!!!!!!!!!!!!!!!! You are so on target here. As my scientist wife keeps saying "doesn't Frank realize that by changing crank length, raising the seat but not also raising the arm pads he's changing two variables each time rather than one

Thanks for the excellent post.

Hugh

Its clear that the only way to confirm all of this properly is to baseline the hell out of everything and then make changes is discrete single variable increments to nail down exactly where these benefits come and go as each change is made. The various permutations and combinations are quite large and would involve multiple bike frames, multiple lengths of cranks, baselined power and ongoing power measurement, all using a wind tunnel for several weeks. (This is all assuming that you use only one rider which again is obviously not correct as no two riders are exactly alike - what works for the test subject is far from guaranteed to work for me)

However, the shortcut I suggested earlier is to power test these combinations outside a windtunnel first and then only take the leading variations into the tunnel. (It is unlikely that a position that is so cramped it causes a drop of 50 Watts is going to overcome that with aero so dont bother testing it, for instance)

Personally, I am impressed that Frank has gone to this step to validate some of the theories and I look forward to seeing the results of the no-doubt considerablly more complicated protocol he uses next time. Its also important to note that Frank has been loud in his listing of known flaws in the tests he has done. its a work in progress

 

[sciguy]

Total agreement on all points.

Well said.

Hugh

 

[TarmacExpert]

If you will examine our data you will see that drag did not depend upon saddle to pad drop and was pretty much constant over a 10 inch difference as the rider became low.

What you saw was the effect of different changes being made at the same time, with opposing effects. If you just move the pads up and down and change nothing else, you'll see drag reduce as you go lower up to a certain point, then it will start to increase again as the back starts to face the wind.

If the upper body and lower body respond differently to the wind then, in a head wind, if we can improve the shape of the upper body, where the wind is the greatest this should more than compensate for the increase seen from the lower body, where the wind is less. You need to get unstuck from your bias and look at the data. Shorter cranks should do relatively better from an aerodynamic perspective in a headwind than they would in still air.

A quick calculation on the effect of wind gradient. Assuming a Hellman exponent of 0.3:
http://en.wikipedia....i/Wind_gradient
With a wind speed of 10kph at 10m above ground level, wind speed would be at:
1.3m 5.42kph
1.2m 5.29kph
So a 0.13kph difference in those 10cm. Definitely not insignificant, but 10kph at 10m is a pretty windy day, and it's still only around 3W at 50kph, and that is assuming that the entire rider+bike package is subject to that different air speed, so it would be less than that in practice.

And, my guess is the people on the drag2zero team when in the wind tunnel are looking at aerodynamic drag exclusively and not looking at what these changes do to power nor at crank length.

The Drag2Zero people try to optimise their overall performance. They broke the UK team 25 mile record the other day:
http://cyclingtimetrials.org.uk/Def...57087&gv484__gvfl0=0&language=en-GB&tabid=109

Mark Holton did that 48:07 with just 327W:
http://teamdrag2zero.co.uk/2012/04/15/d2z-break-national-record/

 

[sciguy]

A quick calculation on the effect of wind gradient. Assuming a Hellman exponent of 0.3:
http://en.wikipedia....i/Wind_gradient
With a wind speed of 10kph at 10m above ground level, wind speed would be at:
1.3m 5.42kph
1.2m 5.29kph
So a 0.13kph difference in those 10cm. Definitely not insignificant, but 10kph at 10m is a pretty windy day, and it's still only around 3W at 50kph, and that is assuming that the entire rider+bike package is subject to that different air speed, so it would be less than that in practice.

Great post and I love your work. I would however contend that 10kph is at 10 meters is a rather calm day.... at least here in PE South Africa. That's only a 6.21mph breeze for those back in the States. If you don't mind run the calculations with a 60kph wind at 10 meters.

Thanks for the very useful tidbit.

Hugh

 

[TarmacExpert]

Great post and I love your work. I would however contend that 10kph is at 10 meters is a rather calm day.... at least here in PE South Africa. That's only a 6.21mph breeze for those back in the States. If you don't mind run the calculations with a 60kph wind at 10 meters.

It will scale linearly with the wind speed, so you can just multiply the figure of 0.13kph by 6, giving 0.78kph.

Here in the UK, many TT courses are reasonably sheltered, so a typical wind speed is only around 4kph at rider height (determined using VE combined with a wind vector to make the VE match the actual elevation). It can be more on less sheltered courses, and some areas are generally more windy than others.

 

[FrankDay]

Actually he did initially test using a used set of adjustable Power Cranks that be purchased cheaply from Ebay. He locked them out so they acted as fixed cranks and tested lengths from 200mm to 165mm. His found the 175s to be the best compromise in terms of comfort and power and aeroness. So scratch that criticism of the list

Could you provide his raw data?

Not sure why you've decided that he is cramped. Mike looks to be holding somewhat of a Superman Position in his pictures. From my experience it's way harder to hold that position for 5+ hours than the one my friend rides.
I would not be surprised tested slightly more aero if he took on Mike's postion but can't imagine holding it for 112 miles.

Well, in Mikes case we weren't trying to optimize power, comfort, or anything. We were looking to see how simply changing torso position via crank length affected wind resistance. Turns out we also saw how changing crank length affected leg wind resistance and these two components seem related.

I keep getting the feeling that you yourself have very little real personal experience riding time trial bikes or using power meters.

Hugh

What does that question, whether true or not, have to do with this data set?

 

[FrankDay]

Ding, Ding , Ding !!!!!!!!!!!!!!! We have a winner!!!!!!!!!!!!!!!!!!! You are so on target here. As my scientist wife keeps saying "doesn't Frank realize that by changing crank length, raising the seat but not also raising the arm pads he's changing two variables each time rather than one

Thanks for the excellent post.

Hugh

Well, I guess I wanted to test it the way I did because that is what I expect my customers to do (actually, my expectation is they will lower the bars when they shorten the cranks and raise the saddle but that is really changing two things at once) and I was looking for information to help them understand what they might expect with such a change. It is called the real world. If I were simply interested in the leg component I guess I would do it your way. I was not. You, of course, are welcome to repeat this study however you feel if best.

 

[FrankDay]

What you saw was the effect of different changes being made at the same time, with opposing effects. If you just move the pads up and down and change nothing else, you'll see drag reduce as you go lower up to a certain point, then it will start to increase again as the back starts to face the wind.

Of course, and if that is what someone wanted to study, that is what they should do. But, I only had two hours and most cyclists are currently riding as low as they can comfortably go because they all currently believe "lower is better". What is to be gained/learned testing what happens if they were to pretzel themselves lower? I suppose we would find it was better at least down to being flat, something everyone already knows. I was trying to see what happens when people simply change crank length and do nothing else, what usually happens in the real world when people do this experiment.

A quick calculation on the effect of wind gradient. Assuming a Hellman exponent of 0.3:
http://en.wikipedia....i/Wind_gradient
With a wind speed of 10kph at 10m above ground level, wind speed would be at:
1.3m 5.42kph
1.2m 5.29kph
So a 0.13kph difference in those 10cm. Definitely not insignificant, but 10kph at 10m is a pretty windy day, and it's still only around 3W at 50kph, and that is assuming that the entire rider+bike package is subject to that different air speed, so it would be less than that in practice.

And, the speed at 0.4 to 0.8m would be even less. Since it appears that shorter cranks increase the relative drag of the legs while decreasing the relative drag of the torso we can see from this data that while overall drag may stay constant in still air it would appear that it would be relatively better to use shorter cranks in a headwind compared to standard length cranks, the stronger the wind the better.

The Drag2Zero people try to optimise their overall performance. They broke the UK team 25 mile record the other day:
http://cyclingtimetrials.org.uk/Def...57087&gv484__gvfl0=0&language=en-GB&tabid=109

Mark Holton did that 48:07 with just 327W:
http://teamdrag2zero.co.uk/2012/04/15/d2z-break-national-record/

Isn't that what everyone tries to do, optimize overall performance? Just had a coach/customer report he just set a course record racing on his PowerCranks - "I set a course record … 33 mph for 11m…on the PowerCranks!…Legal doping, I tell all my athletes." Anyhow, anecdotes are anecdotes. The purpose of this exercise was to gather some useful data to help people to make better decisions in this area. It certainly isn't the final word here but is more than we had before and, hopefully, will motivate some researcher somewhere to do a really good study in this area. The tough part now is understanding how to utilize this initial data to improve your own racing, should you choose to try.

 

[FrankDay]

It will scale linearly with the wind speed, so you can just multiply the figure of 0.13kph by 6, giving 0.78kph.

Here in the UK, many TT courses are reasonably sheltered, so a typical wind speed is only around 4kph at rider height (determined using VE combined with a wind vector to make the VE match the actual elevation). It can be more on less sheltered courses, and some areas are generally more windy than others.

Wind shear will occur off of any fixed surface. So, wind will be less close to a wall compared to in the middle of the street. Just as riding on the painted lines, which are smoother generally than the asphalt, should result in lower rolling resistance. Sometimes it is paying attention to the little things that can save a few seconds.

 

[TarmacExpert]

Of course, and if that is what someone wanted to study, that is what they should do. But, I only had two hours and most cyclists are currently riding as low as they can comfortably go because they all currently believe "lower is better". What is to be gained/learned testing what happens if they were to pretzel themselves lower? I suppose we would find it was better at least down to being flat, something everyone already knows.

What is to be gained is quantifying the aero change by moving up or down. I know one person who went to the tunnel and found that he could move up several cm with essentially no change in aero drag, very useful information for him as it meant there was no point suffering the discomfort and possible loss of power from being lower. If you test a range of saddle to pad drops (and you need to do it in much smaller increments than 4 inches), you can then go away and test power in each position to see which position optimises power vs drag. I know of someone else who is riding in a position that costs him 20W of power output compared to what he used to ride in, but the aero gain is such that he is substantially faster in that position despite the loss of power.

 

[FrankDay]

What is to be gained is quantifying the aero change by moving up or down. I know one person who went to the tunnel and found that he could move up several cm with essentially no change in aero drag, very useful information for him as it meant there was no point suffering the discomfort and possible loss of power from being lower. If you test a range of saddle to pad drops (and you need to do it in much smaller increments than 4 inches), you can then go away and test power in each position to see which position optimises power vs drag. I know of someone else who is riding in a position that costs him 20W of power output compared to what he used to ride in, but the aero gain is such that he is substantially faster in that position despite the loss of power.

You are welcome to go there and repeat this data or do it however you wish. No "study" is ever perfect no will it ever answer every question. I had very limited time and did not know what to expect so I looked at the biggest range I could hoping that I might be able to connect the dots to learn about the intermediate positions for the population as a whole and not for any specific individual. Until someone does something for the first time there is no basis for figuring out how to do it better the second time. Good luck on your effort. Be sure to report back with your results.

 

[acoggan]

Has lowering the entire body been proven to lower drag?

I'm not sure if this is what you mean, but I once field-tested John Cobb's "low sit" position by dropping my saddle and handlebars by 6 cm (while keeping crank length constant). My CdA went down by 0.011 m^2. I didn't think that I could get w/in the required ~10 W of my normal power output with my saddle so low, though, so didn't pursue things any further.

 

[TarmacExpert]

You are welcome to go there and repeat this data or do it however you wish. No "study" is ever perfect no will it ever answer every question. I had very limited time and did not know what to expect so I looked at the biggest range I could hoping that I might be able to connect the dots to learn about the intermediate positions for the population as a whole and not for any specific individual. Until someone does something for the first time there is no basis for figuring out how to do it better the second time. Good luck on your effort. Be sure to report back with your results.

You misunderstand, Frank, I was trying to offer you helpful advice based on knowing what quite a few people have found from wind tunnel visits. As for my own efforts, I have moved from 170mm cranks to 165mm cranks in the past, and I did not change my saddle to pad drop when I made that change, because my torso was already in the most aero position. I made the change because everyone talked all the time about how shorter cranks are more aero, and I didn't particularly think to question it until I got them, fitted them, and started to think about the thigh position issues. I have had a feeling ever since that they have made me less aero, so thanks to your data (and I did thank you for sharing it in my first post on this thread), I have just ordered some 175mm cranks. I will again keep saddle to pad drop constant and see if I can detect an aero difference with field testing compared to 165mm cranks.

 

[FrankDay]

You misunderstand, Frank, I was trying to offer you helpful advice based on knowing what quite a few people have found from wind tunnel visits. As for my own efforts, I have moved from 170mm cranks to 165mm cranks in the past, and I did not change my saddle to pad drop when I made that change, because my torso was already in the most aero position. I made the change because everyone talked all the time about how shorter cranks are more aero, and I didn't particularly think to question it until I got them, fitted them, and started to think about the thigh position issues. I have had a feeling ever since that they have made me less aero, so thanks to your data (and I did thank you for sharing it in my first post on this thread), I have just ordered some 175mm cranks. I will again keep saddle to pad drop constant and see if I can detect an aero difference with field testing compared to 165mm cranks.

I guess if your upper body is already optimal (however one knows?) then moving the handlebars with the seat would be a good idea. However, most of my customers do not fall into that situation and I was looking for data that might help me to explain to them what they might be able to expect in aerodynamic improvement by moving to shorter cranks. While I didn't get the data I wanted directly I, personally, after I contemplated it for a day, found the data very useful and I am, further, especially grateful for this discussion regarding headwind effects - which enlightened me further.

Edit: and according to my data the reason you feel less aero is because you are because you changed your handlebar height when you shortened your cranks. My data indicates that if you had kept your handlebar height constant that it is possible that your "aeroness" would have remained constant.

I am also very appreciative that this thread has actually turned into a discussion instead of the usual vindictive and unthinking personal attacks. Hopefully those that are new to the thread don't try to slog through the entire thing and skip posts 100-1100 or so.

 

[TarmacExpert]

Edit: and according to my data the reason you feel less aero is because you are because you changed your handlebar height when you shortened your cranks. My data indicates that if you had kept your handlebar height constant that it is possible that your "aeroness" would have remained constant.

I actually tested that after the change in crank size. With my bike (Speed Concept), moving the pads up and down is quite time consuming and requires having different length bolts and tools with you, but moving the saddle up and down is easy. So what I did was one field testing session with the pads in one position, and another field testing session with the pads 1cm lower. In each session I moved the saddle up and down 1cm either side of what I already believed to be my optimal saddle to pad drop from previous testing. On both occasions the same saddle to pad drop was again optimal.

I agree that the data you collected are useful. The difficulty you face in trying to extrapolate from testing with one rider is that people vary quite a lot in how their drag responds to changes. My drag changes drastically just 1cm either way from my optimal saddle to pad drop, making it quite easy for me to find the optimal position with field testing, but as I mentioned before I know someone who found in the wind tunnel that his drag barely changes over a range of several cm.

Also, if I were you, I wouldn't bother testing angled arms at all next time. One person who tested that in the tunnel in small increments found that drag immediately got worse as he moved away from horizontal, and only became better in a very specific range higher up. But even then it was only slightly better than horizontal. If that is typical, it's almost certainly not worth the cost of the tunnel time you have to consume to find out where your specific optimal range is. Many of the Drag2Zero riders seem to have perfectly horizontal arms, and Damon Rinard has also said that is optimal for most riders, so I would just stick with that and work on the things that typically have a bigger impact for most riders. BTW this is what Mark Holton's position looks like:

Arms horizontal, and shoulders not all that low relative to his hips.

 

[RChung]

I am claiming benefits in aerodynamics using short cranks that come pretty much automatically, no need for any testing.

Testing is good.

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. 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.

This isn't quite true. I reported the average over a particular loop or lap (not ride) because that's typically the smallest contained unit of complete information riders have. However, if you have complete information for shorter intervals then you can compute the drag over that interval. In particular, with the right data you can compute the drag over the preceding time interval (for example, 1 second). It's true that the drag you'll be computing will be the average over that second. And controlled conditions aren't always necessary -- they make life simpler but the key isn't the control of the conditions but rather the accurate and precise measurement of those conditions.

I can't believe I got sucked into this interminable thread.

 

[FrankDay]

Testing is good.



This isn't quite true. I reported the average over a particular loop or lap (not ride) because that's typically the smallest contained unit of complete information riders have. However, if you have complete information for shorter intervals then you can compute the drag over that interval. In particular, with the right data you can compute the drag over the preceding time interval (for example, 1 second). It's true that the drag you'll be computing will be the average over that second. And controlled conditions aren't always necessary -- they make life simpler but the key isn't the control of the conditions but rather the accurate and precise measurement of those conditions.

But, how does one accurately and precisely measure the "conditions" when using your method, be the interval 1 second or a 10 minute loop? When outside the wind conditions are pretty much constantly changing even if slightly and how does the rider know exactly what position they were in during that interval? I guess it is possible but not easily but hardly worth the effort because conditions will never be exactly replicated. A "pretty good idea" as to what one is doing under different conditions seems like the best anyone can ever expect.

That having been said, one thing the Chung method would be particularly useful for, based upon this discussion, would be to determine the change in relative drag between different positions that might occur between still air and headwinds.