it's a loop course that I'm looking at here - quite good except for one fastish, sharp, blind 90 ...

Tom. A and another person have suggested that approach ... sounded good to me vs. chopping up the file - which would have been my 1st thought. Now that zone must be truly flat of course or another error will be introduced. The loop is 4km and I figure maybe 25-50m to brake ...

edit: but I will admit I've not thought about it as much as I should have!! Setting the VE flat during braking would be fine if braking were the only source of slowing --- but we are very likely to be coasting as well -- so the drop in speed due to drop in power which should be captured will not via this method. Or am I thinking too much?

Darn Tom and his half-pipe!

Exactly. Isn't that the point? Faster is faster, right? :-)



That just indicates that you don't fully understand the approach and the underlying physics of what is being measured. No big deal, a lot of people don't...



What would the purpose of the blinding be (besides perhaps causing the rider to crash)? Remember, the calculation is based on the recorded values of speed and power; Nothing else. Are you thinking that there would be some sort of "placebo effect" in the rider being able to telekinetically change the speed vs. power recording? You might want to think that one through again...




In this case, you'll just have to trust me ;-)

Seriously, what you point out is valid, but is just a part of using good experimental technique. To give you an idea of how well I can apparently "hold a position", in the past I've been able to get repeatability of ~.001 to .002 m^2 between separate runs of the same configuration during a session. Another thing to remember is that the "visual" nature of the technique allows one to see when things "aren't quite right" in that the laps won't be as consistent as they should be (i.e. the virtual elevation calculation "peaks and valleys" will vary inordinately). If you've read the whole thread you'll see that it was the excess variability in the second P3C run that I did which caused me to basically "toss" that run.



Such as? I believe we've covered all the major ones...as Andy says "Asked and answered".



Ummm...from going faster?



No. The ambient atmospheric values in the original posting are correct.

The error was made in that I posted a screenshot of an analysis of a TT I had run in comparing my spreadsheet to another rider's spreadsheet using his values. We were comparing them and I forgot to change the ambient values to the one's I had used. Even so, that "error" only changed the calculated CdA value by .002 m^2.



It could...if you were WAY off on the inputs. But, as I said above, even that "error" only changed the result by .002 m^2...which is ~ the typical precision quoted for wind tunnel testing.

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http://bikeblather.blogspot.com/

I'm shocked...shocked, I say! Frank Day not understanding physics?!? Next thing you'll be telling me is that the Easter Bunny isn't real! ;-)

(BTW, is it just me, or do others here often wonder whether Frank Day and Tom Kunich are related?)

Actually, even just a "quarter pipe" with braking on the bottom portion (i.e. flat) should work pretty well...that might expand your course possibilities...

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http://bikeblather.blogspot.com/

Yes. Which is why I stated it looked like a great technique for the individual to assess themselves.
Ugh, the purpose of blinding is to prevent the imposition of inadvertent bias into the results. Perhaps the rider "wants" the P3 to test better so while on it does things with their head, body, steering, or something else, without being consciously aware of same, that they "know" will make it look better or the P2 to look worse.
Well, since you were not blinded to the tests we can't know if there is any inadvertent bias that you injected to the results based upon your expectations. I don't doubt you did not intend to do so. But, it cannot be categorically excluded that it did not occur because you say "trust me". It is simply good experimental design. Now, it is not always possible to blind the participants to a study. For instance, people certainly know the difference between PowerCranks and regular cranks. But, without blinding the results are always somewhat more suspect when compared to blinding or double blinding. For instance, a current PC study going on right now the person doing the testing is blinded at to what person is doing what. The participants are not blinded, obviously, but the tester/evaluator is. We think that will make for a stronger study. In this instance it seems no one was blinded to anything.
see above
Let me rephrase the question, your honor. Where is the "going faster" coming from?

But, that is not the only potential source of error. How about the accuracy or precision of the power meter? Or, the potential positioning changes? All these potential errors can add up to be large (if they are all in the same direction) or small (if they are all in different directions). Unfortunately, one cannot tell on a single trial.

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Frank,
An original Ironman and the Inventor of PowerCranks

Attorney: "Your Honor!!"

Judge: "Say no more. Move on, Mr. Day, or I will find you in contempt of court."

Frank RTFM

Now why should he do that, when he can just sit on the sidelines and ask inane questions that have already been addressed ad nauseum? :-)

But, that is not the only potential source of error. How about the accuracy or precision of the power meter?

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Tom used the same power meter so even if there was an error in the meter it wouldn't explain the difference between the estimated CdAs.[/reply]

i admit i haven't read all the posts......but how exactly can the positions be identical?

i would assume the two frames have different TT/ST/HT/Seatstay/BB drop lengths and angles, so depending on a person's body dimensions couldn't this vary wildly, anywhere from way better to way worse?

Yes, why indeed? Somewhat similar to answering the same old stuff about PC's coming from those who have never tried them, let alone trained on them yet who seemingly claim to know what they can or cannot do. :-)

Here is my problem in a nutshell. Supposedly this result shows that the aerodynamic improvement seen changing from one Cervelo bike to the P3C would predict a 2 minute savings in a 40K TT. I presume that people have actually raced on this upgraded bicycle like at places like Kona. How come this improvement is not being reflected in the times there?

This result just seems so different than the racing reality. Where is this so-called difference being seen in the real world?

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Frank,
An original Ironman and the Inventor of PowerCranks

Oh, I dunno...maybe Tom actually took the time to, e.g., raise or lower the seat and/or move it back and forth to make certain that they were? Just a thought....

Judge: "Okay, Mr. Day, that's it! I'm finding you in contempt of court and fining you $1000 for repeatedly asking questions that have already been answered in this thread. Do it again, and I'll have the bailiff lock you up!"

gee thanks for the jack ass answer to my legitimate question....did you perhaps take the time to read the second part of my question?

I did.

I have to agree with you. Even if it was a very stupid question, Andrew Coggan was totally out of line when using such a sarcastic tone. Especially because, being the question so stupid, there is the danger that you are not intelligent enough to understand his sarcasm.

Would this have helped?

[/reply]
I have to agree with you. Even if it was a very stupid question, Andrew Coggan was totally out of line when using such a sarcastic tone. Especially because, being the question so stupid, there is the danger that you are not intelligent enough to understand his sarcasm.[/reply]
didn't sound sarcastic, and didn't at all answer my question. point is there's no way you're going to get the exact same results on two different bikes that have different dimensions and geometries even with the "same position", particularly for riders of different dimensions. especially not 2 minutes worth. maybe it did work for Tom, but not a rule of thumb by any stretch. funny how none of this applies in the real world

I have to agree with you. Even if it was a very stupid question, Andrew Coggan was totally out of line when using such a sarcastic tone. Especially because, being the question so stupid, there is the danger that you are not intelligent enough to understand his sarcasm.[/reply]
didn't sound sarcastic, and didn't at all answer my question. point is there's no way you're going to get the exact same results on two different bikes that have different dimensions and geometries even with the "same position", particularly for riders of different dimensions. especially not 2 minutes worth. maybe it did work for Tom, but not a rule of thumb by any stretch. funny how none of this applies in the real world[/reply] So despite talking about the rider's position, and how the geometries of the bikes may have been different, by "this" you really meant the time differential itself? Now that certainly makes a lot of sense...

I have to agree with you. Even if it was a very stupid question, Andrew Coggan was totally out of line when using such a sarcastic tone. Especially because, being the question so stupid, there is the danger that you are not intelligent enough to understand his sarcasm.[/reply]
didn't sound sarcastic, and didn't at all answer my question. point is there's no way you're going to get the exact same results on two different bikes that have different dimensions and geometries even with the "same position", particularly for riders of different dimensions. especially not 2 minutes worth. maybe it did work for Tom, but not a rule of thumb by any stretch. funny how none of this applies in the real world[/reply] Have you ever recorded the x/y coordinates from the bottom bracket to the seat and from the bottom bracket to the arm rests.

4 numbers are all that is required to set up an identical position on two bikes.

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Erik
Strava

It could, if the precision of the meter is not perfect. Since no measurement device is perfect, we can presume some error could come from this. Only question is, how much? What is the precision of the meter he used?

But, more than this. He is attributing all of the change to the bicycle. This is ludicrous in view of the fact we are talking about humans on a bicycle. It is simply impossible for them to be exactly the same on these different trials. The overall result could be entirely accurate but to attribute the change entirely to the difference in bicycle frames seems a bit of a stretch.[/reply]

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Frank,
An original Ironman and the Inventor of PowerCranks

[/reply] So despite talking about the rider's position, and how the geometries of the bikes may have been different, by "this" you really meant the time differential itself? Now that certainly makes a lot of sense...[/reply]
so you're implying that the height of the head tube makes no difference, the fact that one seat tube and down tube is longer makes no difference, the fact that one seat tube is longer makes no difference........as long as his position is the same who cares? what if he had say chosen a 56cm instead of a 54cm etc frame? it's interesting, but certainly doesn't tell the whole story, and certainly not for every rider, just in the specific instance. which is fine, i was just trying to bring up a possible conflict when applying this broad spectrum

[/reply] Have you ever recorded the x/y coordinates from the bottom bracket to the seat and from the bottom bracket to the arm rests.

4 numbers are all that is required to set up an identical position on two bikes.[/reply]
yes, i'm agreeing you can achieve the same body position (maybe i should have worded it differently in the first place) but that same body position isn't going to apply the same on a totally different frame.

for a real world example, i went from a P3C last year to an Al P3 this year just to save some money, identical body position, and i'm definitely not slower

So despite talking about the rider's position, and how the geometries of the bikes may have been different, by "this" you really meant the time differential itself? Now that certainly makes a lot of sense...[/reply] so you're implying that the height of the head tube makes no difference, the fact that one seat tube and down tube is longer makes no difference, the fact that one seat tube is longer makes no difference........as long as his position is the same who cares? what if he had say chosen a 56cm instead of a 54cm etc frame? it's interesting, but certainly doesn't tell the whole story, and certainly not for every rider, just in the specific instance. which is fine, i was just trying to bring up a possible conflict when applying this broad spectrum[/reply]
I agree. If the bikes are not exactly the same, and only the positions are the same, what is the point of all this testing??? Seriously...

[/reply] But, more than this. He is attributing all of the change to the bicycle. This is ludicrous in view of the fact we are talking about humans on a bicycle. It is simply impossible for them to be exactly the same on these different trials. The overall result could be entirely accurate but to attribute the change entirely to the difference in bicycle frames seems a bit of a stretch.[/reply]
that's what i'm trying to say