Mo Mo Ya(w)

[Andrew_Coggan]

WARNING: semi-rhetorical navel-gazing below!

A semi-random post spurred by various things (listed in no particular order, except for perhaps the last):

1. an off-hand comment by Gerard about CdA at 0 deg of yaw being dominated by frontal area;

2. the results of wind tunnel tests I/we have performed at TAMU comparing:

A. the Superman vs. a standard aero position
B. Blackwell vs Zipp wheels
C. the effects of 75 vs. 80 cm of reach
D. the effects of cardboard fairings added to an aero helmet (don’t know if I’ve posted these results)

which clearly demonstrated that what happens at 0 deg of yaw rarely tells the full story;

3. the fact that only once have I measured an iron-clad difference in CdA using the field test approach (which happened to result from changing tires);

4. the fact that my CdA back-calculated from TTs performed in non-still air is invariably lower than that measured in formal field tests conducted under still-air conditions (i.e., at/near 0 deg of yaw); and finally

5. the results of some field tests performed by an elite athlete that I just had the opportunity to analyze.

Given the above, I have to ask: is field testing to measure CdA (which, to obtain truly precise results, must be performed when there is very little wind) really worth it?

[Khai]

Am I the only one who saw this thread and thought “dyslexic cellist”?

[Andrew_Coggan]

Am I the only one who saw this thread and thought “dyslexic cellist”?

I hope not.

[PeaTearGriffin]

Am I the only one who saw this thread and thought “dyslexic cellist”?

That’s the reason I clicked this thread.

[Former_User]

Given the above, I have to ask: is field testing to measure CdA (which, to obtain truly precise results, must be performed when there is very little wind) really worth it?

IME…it has been WAY “worth it”…YMMV

BTW, CdA differentials “back-calculated” from my TTs tend to match the differentials I’ve seen in field testing…for example, see the “Something Borrowed…Something Fast!” thread.

[jackmott]

yes, but you need to do it on a short loop with moderate and constant wind

I have one near me!

=)

Given the above, I have to ask: is field testing to measure CdA (which, to obtain truly precise results, must be performed when there is very little wind) really worth it?

[Andrew_Coggan]

Given the above, I have to ask: is field testing to measure CdA (which, to obtain truly precise results, must be performed when there is very little wind) really worth it?

IME…it has been WAY “worth it”…YMMV

Of course, it all depends on where you start (and I don’t mean that in any negative way). The point of my post was really just to emphasize the importance of not just focusing on measurements made at/near 0 deg of yaw (or even at a single, fixed yaw angle of, e.g., 7 deg).

BTW, CdA differentials “back-calculated” from my TTs tend to match the differentials I’ve seen in field testing…for example, see the “Something Borrowed…Something Fast!” thread.

That implies to me that you normally TT under fairly calm conditions, and/or you don’t “sail” as well as I do (and in fact, my experience is similar to yours in that:

1. the difference between my field-test-derived and my back-calculated CdA is minimal if it was relatively calm during the TT, and

2. relative to my competition, I don’t seem to be hurt as much by wind).

[Former_User]

Given the above, I have to ask: is field testing to measure CdA (which, to obtain truly precise results, must be performed when there is very little wind) really worth it?

IME…it has been WAY “worth it”…YMMV

Of course, it all depends on where you start (and I don’t mean that in any negative way). The point of my post was really just to emphasize the importance of not just focusing on measurements made at/near 0 deg of yaw (or even at a single, fixed yaw angle of, e.g., 7 deg).

BTW, CdA differentials “back-calculated” from my TTs tend to match the differentials I’ve seen in field testing…for example, see the “Something Borrowed…Something Fast!” thread.

That implies to me that you normally TT under fairly calm conditions, and/or you don’t “sail” as well as I do (and in fact, my experience is similar to yours in that:

1. the difference between my field-test-derived and my back-calculated CdA is minimal if it was relatively calm during the TT, and

2. relative to my competition, I don’t seem to be hurt as much by wind).

Well…to be complete, it also could imply one more thing…that I TT faster than you But, you and I both know that isn’t true…yet

[Alex_Simmons]

Given the above, I have to ask: is field testing to measure CdA (which, to obtain truly precise results, must be performed when there is very little wind) really worth it?

Hmmm, don’t know what happened to my last response… disappeared…

Anyway, 'cause it’s fun?

I remember a trial pursuit I did outdoor on a really windy evening a few years back. I was surprised at the (good for me) time considering the conditions. Might go back and do an effective CdA estimate compared to indoor pursuits.

[RChung]

Given the above, I have to ask: is field testing to measure CdA (which, to obtain truly precise results, must be performed when there is very little wind) really worth it?

Hmmm. Shorter Andy: wind tunnels? They’re more real than the real world.

[Andrew_Coggan]

Anyway, 'cause it’s fun?

No disagreement here.

[Andrew_Coggan]

Given the above, I have to ask: is field testing to measure CdA (which, to obtain truly precise results, must be performed when there is very little wind) really worth it?

Hmmm. Shorter Andy: wind tunnels? They’re more real than the real world.
As I indicated the other day, I definitely think this is best the way to go (provided you have access to one/can afford it, of course).

[Andrew_Coggan]

it also could imply one more thing…that I TT faster than you But, you and I both know that isn’t true…yet

In your dreams.

[roady]

well, in my effort to give you a new signature, I’ll simply ask ‘who ever thought that field-testing at zero yaw was a good idea?’

You hit on one of the reasons I’m much more comfortable field testing on a windless day on an outdoor track. With some very sophisticated measuring devices (some pieces of string attached to my handlebars), I know I’m incorporating some segments up to 8 to maybe 10 degrees. While I don’t know the ‘average’ yaw, it does give me confidence that the results are more ‘real world’ that a flat, windless out-and-back. I’m also helped by the fact that I’m concerned more about ‘low yaw situations’, since I’m reasonably fast and most of the courses on which I race aren’t really that windy.

That said, I really haven’t made a lot of changes based on field testing. As a matter of fact the only real conclusions I’ve reached are that a) an aero bottle on an aluminum P3 doens’t hurt, and may help a little, b) the Flandis is really, really slow for me, and c) narrow elbow is no faster (and maybe a little slower) than having them the same width as my hips (at least with the same arm angle).

Here’s what’s worked the most for me WRT position changes, in order of importance:

-a mirror

-a camera, with movie mode

-my eyeball wind tunnel

-back calc’ing stand-alone CdA from events

-still photos from race photographers

-field testing

[roady]

since there really is no ‘topic’, I guess this isn’t OT…

One thing I’m wondering about is your ‘superman deteriorating at yaw’ deal. Was that on the Hooker–and doesn’t that bike stall significantly? I’m wondering if the reason it deteriorates at yaw is because less of the bike is ‘covered’, and I wonder if you’d have the same experience on a more modern frame? The reason I wonder is that my lowest stand-alone CdA (and my wife’s) has been in a straight cross wind–and while I’m not as stretched as she is, my arm angle is probably >45 degrees when I’m fully ‘tucked down’.

Any thoughts?

[Former_User]

it also could imply one more thing…that I TT faster than you But, you and I both know that isn’t true…yet

In your dreams.

Oh, I’m definitely closing the gap…have I mentioned the power levels I’ve been maintaining in some TT intervals lately?

Besides…since you don’t even HAVE a TT bike right now (as far as I know anyway…have you put the order in for the P4 yet?), I’m fairly sure I could give you a pretty good “run for your money” with you riding whatever is left in your “quiver”

[Former_User]

well, in my effort to give you a new signature, I’ll simply ask ‘who ever thought that field-testing at zero yaw was a good idea?’

Ummm…I dunno, but I recall that these guys seemed to think that field testing matched up with wind tunnel results fairly well:

Martin JC, Milliken DL, Cobb JE, McFadden KL, Coggan AR. Validation of a mathematical model for road cycling power. J Appl Biomech 1998; 14:276-291.

[roady]

well, in my effort to give you a new signature, I’ll simply ask ‘who ever thought that field-testing at zero yaw was a good idea?’

Ummm…I dunno, but I recall that these guys seemed to think that field testing matched up with wind tunnel results fairly well:

Martin JC, Milliken DL, Cobb JE, McFadden KL, Coggan AR. Validation of a mathematical model for road cycling power. J Appl Biomech 1998; 14:276-291.

well, it was a rhetorical question… however, at what yaw angles do field tests and wind tunnel results ‘match up fairly well’? Zero?? In that case, I’d say ‘field testing at zero yaw is as useful as wind tunnel testing at zero yaw’.

If field testing at zero yaw matches up ‘fairly well’ with a bell curve wind tunnel results of the most commonly seen yaw angles, then I’d ask “how well is ‘fairly well’”

[Former_User]

well, in my effort to give you a new signature, I’ll simply ask ‘who ever thought that field-testing at zero yaw was a good idea?’

Ummm…I dunno, but I recall that these guys seemed to think that field testing matched up with wind tunnel results fairly well:

Martin JC, Milliken DL, Cobb JE, McFadden KL, Coggan AR. Validation of a mathematical model for road cycling power. J Appl Biomech 1998; 14:276-291.

well, it was a rhetorical question… however, at what yaw angles do field tests and wind tunnel results ‘match up fairly well’? Zero?? In that case, I’d say ‘field testing at zero yaw is as useful as wind tunnel testing at zero yaw’.

If field testing at zero yaw matches up ‘fairly well’ with a bell curve wind tunnel results of the most commonly seen yaw angles, then I’d ask “how well is ‘fairly well’”

IIRC, some of the field testing for that paper was done in fairly windy conditions…I gotta think there was some significant “yaw component” in that analysis…

[Alex_Simmons]

Given the above, I have to ask: is field testing to measure CdA (which, to obtain truly precise results, must be performed when there is very little wind) really worth it?

Hmmm, don’t know what happened to my last response… disappeared…

Anyway, 'cause it’s fun?

I remember a trial pursuit I did outdoor on a really windy evening a few years back. I was surprised at the (good for me) time considering the conditions. Might go back and do an effective CdA estimate compared to indoor pursuits.

OK, I went back and dug out that file. It was Jan-07, so only a couple of years ago. Seems like more.

Anyway, looking at a VE and taking a Crr of 0.0035 for concrete (vs the 0.0028 I used for the wooden boards), I got a CdA of ~0.22 m^2 from that very windy day at the track.

Then I took a pursuit file from State champs at DGV two months later, same bike/set up except I used the front disk instead of the shamal (and the 0.0028 Crr). What do I get? ~0.22 m^2 LOL!

I can’t believe I was that slippery. Big ol’ rugby shoulders me. Given I last weighed in at ~ 0.26 m^2 on the same bike the other weekend I sure have some ground to make up!

Anyway, I don’t know for sure the actual Crr in each case, so each CdA estimate could move up/down a bit but I think those values are at least reasonable.

Virtual Elevation/power/speed plots below.

This is the outdoor windy evening on concrete 333.3m track. You can see how the speed varied depending on the direction I was going. Each lap has a smaller and a higher peak speed for the bends/straights. Winds reported at ~ 11m/s but of course what was down at trackside inside the drome would be different, not that fast but windy enough.

And the indoor boards 250m track 8 weeks later (note the Phinney-like pacing but not the Phinney-like power LOL):