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Re: Something borrowed...something FAST! [roady] [ In reply to ]
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Hmm... While I wouldn't completely discount the possibility of PM error, given the hub you used for the testing I'd bet that it's unlikely. So, unless you were just trying harder on the P3C, that really leaves one likely alternative: you're lying and you made the whole thing up--probably so more people would buy Cervelos and not have any money left for PowerCranks! My money is on this one.

Mine is on Ninjas. ;-)
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Re: Something borrowed...something FAST! [Andrew Coggan] [ In reply to ]
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Hmm... While I wouldn't completely discount the possibility of PM error, given the hub you used for the testing I'd bet that it's unlikely. So, unless you were just trying harder on the P3C, that really leaves one likely alternative: you're lying and you made the whole thing up--probably so more people would buy Cervelos and not have any money left for PowerCranks! My money is on this one.

Mine is on Ninjas. ;-)
Man, those Ninjas are busy--from Spain to Santa Barbara....
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Re: Something borrowed...something FAST! [roady] [ In reply to ]
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So, unless you were just trying harder on the P3C, that really leaves one likely alternative: you're lying and you made the whole thing up--probably so more people would buy Cervelos and not have any money left for PowerCranks! My money is on this one.

Damn! I've been found out...shit. ;-)

Actually, from what I've learned, I'd appreciate it if people didn't buy P3Cs...especially ones I have to race against on my P2K still.



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After all, look at what pros do. It's not like riders with P3C's are at a competitive advantage or anything. I mean, it's not like 40% (at least) of the top 10 are riding P3C's or anything--despite the fact that a couple of those riders aren't sponsored by Cervelo. Hmmm.......

Well, you know what they say...you never know if a pro is successful "because of" or "in spite of" what they do, right? :-)

http://bikeblather.blogspot.com/
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Re: Something borrowed...something FAST! [Tom A.] [ In reply to ]
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That's an interesting idea...

Not mine, damn it. That's how Adam does it. I had the closed-form solution but didn't notice that it worked for any segment with known elevation change. I was restricting it to laps so the elevation nets to zero and the PE term drops out. In my defense, I rarely know the true elevation change but in this case you do. [Edit:] You also have to know the exact lap length which I often don't until after I've made an initial guess at Crr and CdA.
Last edited by: RChung: May 29, 08 10:16
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Re: Something borrowed...something FAST! [Andrew Coggan] [ In reply to ]
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Glad I'm entertaining someone as well as aggravating Drs Chung and Coggan!

Mostly I think you're making a fool of yourself. It's all well and good to be skeptical, but taken to the extreme (as you and others have done) it just becomes close-mindedness. After all, it's not as if anyone has ever presented any quantitative data that directly conflicts with Tom's or my observations. IOW, everything - wind tunnel tests, formal field tests using a powermeter, back-calculation from TT performances - point to there being a significant difference in drag between the P2k and the P3C. Yet, you and others still refuse to believe it, just as some deny the existence of evolution or global warming.
Some would say it's foolish and weak-minded to resort to personal insults on an internet forum, but I'm not one to pass those sorts of judgements.

You raise an interesting point here: if there is such overwhelming and converging data to suggest that the P3C is faster than the P2K by 2s/km, then what was the purpose of Tom's study? I would think one of the main aims of the study would be to validate Dr Chung's method of field testing. I was simply pointing out that there are a number of flaws in the study design (as executed by Tom) that leave it open to deliberate manipulation and/or cognitive biases the effects of which are very well documented.

If these biases, manifested as position changes, account for a substantial portion of the delta CdA Tom demonstrated for the P3C/P2K runs, a portion we have no means by which to retrospectively estimate, this means that his data can not be used to support a 2s/km rule of thumb. That's not to suggest that a 2s/km rule hasn't been supported by wind tunnel tests, by back-calculating TT performances, or other field tests. I don't have the experience with other tests of these two frames to comment on them; I'm simply commenting on the study Tom executed.
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Re: Something borrowed...something FAST! [RChung] [ In reply to ]
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The suggestion on this thread has been that, all else being equal, the difference in aerodynamics between the P3C and P2K frames results in 2 s/km time savings. This is only supported by Tom's data if we accept that all of the .023m^2 is due to frame aerodynamics alone and not rider positional changes or power meter inaccuracies. We have to be able to attribute all of the delta CdA to the frame alone for it to be true. This is where I think Tom's study design is weak. Without blinding we don't know whether he made systematic changes to his position to make it more aerodynamic on the P3C, therefore we can't attribute all of the delta CdA to frame aerodynamics alone, which invalidates the 2s/km estimates.

As roady has introduced to the discussion, the power meter may have read differently in early and late runs and, since Tom didn't alternate runs, this would introduce major systematic bias in favour of the P3C.

1. You know this phrase "all else being equal?" I don't think it means what you think it means.
2. Once again, you're reverting to the claim that any error invalidates all difference.
You misunderstand me. On this thread, the "all else being equal" caveat has been used like this: "if Rider X rides a P3C he will be 2s/km faster than if he rides a P2K, all else being equal." While this may be true, I do not feel that Tom's study provides strong evidence of it, due to the threats to validity inherent in the study design.

The way you're implying "all else being equal" should be used is like this: "Tom's study shows that a P3C is 2s/km faster than a P2K, all else being equal." The point is that Tom's study design doesn't fill me with confidence that all else was equal, in that it does not effectively deal with the potential for cognitive bias. To be clear, I'm saying that I think there's a good chance that all was not equal. Therefore making claims based on the assumption that all was equal becomes a nonsense.

I'm not reverting to the claim that any error invalidates all difference. I'm pointing out that a 2s/km rule of thumb relies on all of the observed delta CdA being attributable to the frame. If that's not the case, and part of the delta CdA is attributable not to frame aerodynamics but to a systematic difference in body position, then a 2s/km rule of thumb is invalid, as it is not supported by the data. That's not to say that the P3C is no faster than the P2K. Speaking hypothetically, if body position accounted for half of the delta CdA, then maybe the accurate rule of thumb to draw from Tom's study is that the P3C is 1s/km faster.

On the other hand, if a systematic difference in body position exists, the magnitude of which we:
a) have no means to accurately estimate retrospectively, based on the available data; and
b) know could potentially account for all of the CdA delta observed in this study (based on wind tunnel testing such as that described earlier in this thread),

wouldn't that seriously undermine the validity of Tom's findings?
Last edited by: donm: May 29, 08 13:29
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Re: Something borrowed...something FAST! [donm] [ In reply to ]
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The suggestion on this thread has been that, all else being equal, the difference in aerodynamics between the P3C and P2K frames results in 2 s/km time savings. This is only supported by Tom's data if we accept that all of the .023m^2 is due to frame aerodynamics alone and not rider positional changes or power meter inaccuracies. We have to be able to attribute all of the delta CdA to the frame alone for it to be true. This is where I think Tom's study design is weak. Without blinding we don't know whether he made systematic changes to his position to make it more aerodynamic on the P3C, therefore we can't attribute all of the delta CdA to frame aerodynamics alone, which invalidates the 2s/km estimates.

As roady has introduced to the discussion, the power meter may have read differently in early and late runs and, since Tom didn't alternate runs, this would introduce major systematic bias in favour of the P3C.

1. You know this phrase "all else being equal?" I don't think it means what you think it means.
2. Once again, you're reverting to the claim that any error invalidates all difference.
You misunderstand me. On this thread, the "all else being equal" caveat has been used like this: "if Rider X rides a P3C he will be 2s/km faster than if he rides a P2K, all else being equal." While this may be true, I do not feel that Tom's study provides strong evidence of it, due to the threats to validity inherent in the study design.

The way you're implying "all else being equal" should be used is like this: "Tom's study shows that a P3C is 2s/km faster than a P2K, all else being equal." The point is that Tom's study design doesn't fill me with confidence that all else was equal, in that it does not effectively deal with the potential for cognitive bias. To be clear, I'm saying that I think there's a good chance that all was not equal. Therefore making claims based on the assumption that all was equal becomes a nonsense.

I'm not reverting to the claim that any error invalidates all difference. I'm pointing out that a 2s/km rule of thumb relies on all of the observed delta CdA being attributable to the frame. If that's not the case, and part of the delta CdA is attributable not to frame aerodynamics but to a systematic difference in body position, then a 2s/km rule of thumb is invalid, as it is not supported by the data. That's not to say that the P3C is no faster than the P2K.

On the other hand, if a systematic difference in body position exists, the magnitude of which we:
a) have no means to accurately estimate retrospectively, based on the available data; and
b) know could potentially account for all of the CdA delta observed in this study (based on wind tunnel testing such as that described earlier in this thread),

wouldn't that seriously undermine the validity of this study?

The rule of thumb does not depend on the source(s) of the difference in CdA.
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Re: Something borrowed...something FAST! [donm] [ In reply to ]
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if there is such overwhelming and converging data to suggest that the P3C is faster than the P2K by 2s/km, then what was the purpose of Tom's study?

To provide further corrobaration? Because Tom finds such stuff fun? Because his wife won't loan him her P3C, and so he needs additional data to convince her that he needs one of his own? ;-)

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I would think one of the main aims of the study would be to validate Dr Chung's method of field testing.

That would only be possible if Tom's CdA were determined using some independent means (e.g., wind tunnel testing, or even field testing using a powermeter using either the regression or constant speed approach).

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I was simply pointing out that there are a number of flaws in the study design (as executed by Tom) that leave it open to deliberate manipulation and/or cognitive biases the effects of which are very well documented.

That "...number of flaws..." being? So far all you've done is put forth the rather far-fetched hypothesis that, despite setting up the bikes identically, he somehow adopted a position on the P3C that resulted in a significant reduction in drag vs. his well-honed position on the P2k. As Robert already said,

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If these biases, manifested as position changes, account for a substantial portion of the delta CdA Tom demonstrated for the P3C/P2K runs, a portion we have no means by which to retrospectively estimate, this means that his data can not be used to support a 2s/km rule of thumb. That's not to suggest that a 2s/km rule hasn't been supported by wind tunnel tests, by back-calculating TT performances, or other field tests. I don't have the experience with other tests of these two frames to comment on them; I'm simply commenting on the study Tom executed.

No, you're simply demonstrating that you don't know the difference between healthy skepticism and denial.
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Re: Something borrowed...something FAST! [RChung] [ In reply to ]
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That's an interesting idea...

Not mine, damn it. That's how Adam does it.

??

Wasn't your proposal simply to calculate CdA using the "brute force" approach, i.e., ignoring the possible impact of wind?
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Re: Something borrowed...something FAST! [RChung] [ In reply to ]
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The rule of thumb that "a delta CdA of X yield a time savings of Ys/km" does not rely on the source(s) of the difference in CdA.

The rule of thumb that "a P3C frame is 2s/km faster than a P2K frame" clearly implies that the frame is the source of the difference in CdA.

I am referring to the latter rule of thumb when I use the term "rule of thumb".

Are we clear?
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Re: Something borrowed...something FAST! [Andrew Coggan] [ In reply to ]
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So far all you've done is put forth the rather far-fetched hypothesis that, despite setting up the bikes identically, he somehow adopted a position on the P3C that resulted in a significant reduction in drag vs. his well-honed position on the P2k.

Just to clarify, you think that observer expectancy and subject expectancy effects are far-fetched? They do sound far-fetched until you realise how powerful and well-supported by a massive body of literature they are. As both subject and observer in his study, the potential for Tom's expectancy to bias the results is enormous. If you design a study like this, you may find what you expect to find, but it doesn't make it true.

Think outside your engineer box.

Last edited by: donm: May 29, 08 13:47
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Re: Something borrowed...something FAST! [donm] [ In reply to ]
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So far all you've done is put forth the rather far-fetched hypothesis that, despite setting up the bikes identically, he somehow adopted a position on the P3C that resulted in a significant reduction in drag vs. his well-honed position on the P2k.

Just to clarify, you think that observer expectancy and subject expectancy effects are far-fetched? They do sound far-fetched until you realise how powerful and well-supported by a massive body of literature they are. As both subject and observer in his study, the potential for Tom's expectancy to bias the results is enormous. If you design a study like this, you may find what you expect to find, but it doesn't make it true.

Think outside your engineer box.

As someone who has far more experience in this area than you do, I think that the magnitude of the difference that you're proposing is far-fetched.

Oh, and BTW: I'm a physiologist, not an engineer.
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Re: Something borrowed...something FAST! [Andrew Coggan] [ In reply to ]
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That's an interesting idea...

Not mine, damn it. That's how Adam does it.

??

Wasn't your proposal simply to calculate CdA using the "brute force" approach, i.e., ignoring the possible impact of wind?

I'm not sure ignoring wind is brute force. I can brute force it without wind or, if I have windspeed info, I can brute force it with.

I've always said there was a closed-form solution. I had proposed an approach that uses laps so that I could net out the elevation gain. Adam pointed out that if we knew the elevation gain over arbitrary segments then we could look at just those segments piece by piece rather than closed-end laps. In Tom's case, he thinks he knows the net elevation gain so he can just add a term for the change in PE.

I always begin with the iterative fitting because it gives me an indication when things got screwed up and it helps to nail down lap length (solutions using a PE term turns out to be sensitive to getting the lap length right).

Anyway, calculating the still air equivalent CdA gives Tom a couple of additional contrasts for his analysis.
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Re: Something borrowed...something FAST! [RChung] [ In reply to ]
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That's an interesting idea...

Not mine, damn it. That's how Adam does it.

??

Wasn't your proposal simply to calculate CdA using the "brute force" approach, i.e., ignoring the possible impact of wind?

I'm not sure ignoring wind is brute force. I can brute force it without wind or, if I have windspeed info, I can brute force it with.
Call it what you want, but what I mean is back-calculating CdA from the measured power, speed, mass, air density, and, if known, elevation and wind, by simply averaging all of the data together. People have been doing that as long as on-bike powermeters have been available, so there's nothing new (as far as I can tell) in what you proposed that Tom do earlier in this thread.
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Re: Something borrowed...something FAST! [donm] [ In reply to ]
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The rule of thumb that "a delta CdA of X yield a time savings of Ys/km" does not rely on the source(s) of the difference in CdA.

The rule of thumb that "a P3C frame is 2s/km faster than a P2K frame" clearly implies that the frame is the source of the difference in CdA.

I am referring to the latter rule of thumb when I use the term "rule of thumb".

Are we clear?

Perhaps English is not your native tongue, or perhaps you are unfamiliar with the term "rule of thumb." What you're calling a rule of thumb? I don't think it means what you think it means.
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Re: Something borrowed...something FAST! [Andrew Coggan] [ In reply to ]
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Kind of late in arriving, but I thought I would say.

Thank you Tom A. for your clarity and openness. I think of all the people with some amount of knowledge about the deeper workings of bikes you are one of the most open.

The results are bigger than I would have imagined, but not so much that I find them suspect. If you pick things apart, starting big and getting smaller it doesn't seem like so much.

Rear wheel coverage (some old data I had saved on my computer says the difference between the eyre and P2 was about 70 grams, only difference was a bladed seattube with a cutout)
Bladed seatstays(sitting inbetween a spinning wheel and feet, either they're irrelevant or very important I would imagine)
the sculpted, deeper head tube area
deeper seattube/seatpost
smoother transitions from tube to tube

Reminds me of an old saying, "speed is in the details".

Now if only I could get myself a P2C/TTX/P3C.
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Re: Something borrowed...something FAST! [Andrew Coggan] [ In reply to ]
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That's an interesting idea...

Not mine, damn it. That's how Adam does it.

??

Wasn't your proposal simply to calculate CdA using the "brute force" approach, i.e., ignoring the possible impact of wind?

I'm not sure ignoring wind is brute force. I can brute force it without wind or, if I have windspeed info, I can brute force it with.
Call it what you want, but what I mean is back-calculating CdA from the measured power, speed, mass, air density, and, if known, elevation and wind, by simply averaging all of the data together. People have been doing that as long as on-bike powermeters have been available, so there's nothing new (as far as I can tell) in what you proposed that Tom do earlier in this thread.

What I was proposing was that Tom use the CdAs he got out of that to construct new VE profiles for the 2007 and 2008 TTs. Then he'd have a couple of extra contrasts: 2007 vs. 2008 using the measured zero-yaw CdAs, 2007 vs. 2008 using these still air elevation-controlled CdAs, 2007 measured zero-yaw vs. 2007 still air elevation-controlled, and 2008 measured zero-yaw vs. 2008 still air elevation-controlled.
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Re: Something borrowed...something FAST! [donm] [ In reply to ]
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Just to clarify, you think that observer expectancy and subject expectancy effects are far-fetched? They do sound far-fetched until you realise how powerful and well-supported by a massive body of literature they are. As both subject and observer in his study, the potential for Tom's expectancy to bias the results is enormous. If you design a study like this, you may find what you expect to find, but it doesn't make it true.

When your kid's forehead feels hot, do you hand the thermometer to 8 different people to take her temperature? If not, how do you know that your observer expectancy hasn't rendered any rule of thumb that says, "my kid's temperature is 40C and needs to be reduced" invalid?
Last edited by: RChung: May 29, 08 14:34
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Re: Something borrowed...something FAST! [RChung] [ In reply to ]
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Just to clarify, you think that observer expectancy and subject expectancy effects are far-fetched? They do sound far-fetched until you realise how powerful and well-supported by a massive body of literature they are. As both subject and observer in his study, the potential for Tom's expectancy to bias the results is enormous. If you design a study like this, you may find what you expect to find, but it doesn't make it true.

When your kid's forehead feels hot, do you hand the thermometer to 8 different people to take her temperature? If not, how do you know that your observer expectancy hasn't rendered any rule of thumb that says, "my kid's temperature is 40C and needs to be reduced" invalid?
I don't have any kids. Ask me again in a few years.

Of course biases are at play in our day-to-day lives, in everything we do, at all times. The extent to which we're concerned with eliminating those biases varies depending on the context. Your example is hardly relevant to the context of scientific research, or even to internet-reported field tests masquerading as research.

Oh, and the scenario you describe above is part of the reason why doctors/nurses/healthcare professionals prefer to measure a sick child's temperature themselves, rather than relying on parental reports.
Last edited by: donm: May 29, 08 16:43
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Re: Something borrowed...something FAST! [RChung] [ In reply to ]
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Just to clarify, you think that observer expectancy and subject expectancy effects are far-fetched? They do sound far-fetched until you realise how powerful and well-supported by a massive body of literature they are. As both subject and observer in his study, the potential for Tom's expectancy to bias the results is enormous. If you design a study like this, you may find what you expect to find, but it doesn't make it true.

When your kid's forehead feels hot, do you hand the thermometer to 8 different people to take her temperature? If not, how do you know that your observer expectancy hasn't rendered any rule of thumb that says, "my kid's temperature is 40C and needs to be reduced" invalid?
While this seems like a straight forward example, taking a temperature, while seeming simple, is filled with potential error. Most of the errors would lead to a "too low" reading but some can result in "too high". Was the thermometer shook down properly after the last temp for instance. Or, did mom just give the kid some hot soup or tea and you come in to take the temperature. The kid may try to manipulate the temperature if he knows the right number will keep him out of school or keep him out of the ice bath.

It is unlikely that observer bias would play a role in taking a temperature, but it certainly does in taking a simple measurement like blood pressure. People keep taking it until they get the number they want, then take that one.

All measurements are prone to error and due care must be used in both obtaining the measurement and in interpreting it (if the kids temp is measured as 40C but he is happily playing video games, does one necessarily believe it?).

--------------
Frank,
An original Ironman and the Inventor of PowerCranks
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Re: Something borrowed...something FAST! [RChung] [ In reply to ]
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The rule of thumb that "a delta CdA of X yield a time savings of Ys/km" does not rely on the source(s) of the difference in CdA.

The rule of thumb that "a P3C frame is 2s/km faster than a P2K frame" clearly implies that the frame is the source of the difference in CdA.

I am referring to the latter rule of thumb when I use the term "rule of thumb".

Are we clear?

Perhaps English is not your native tongue, or perhaps you are unfamiliar with the term "rule of thumb." What you're calling a rule of thumb? I don't think it means what you think it means.
I'll leave it to those reading this thread to determine which one of us is the more likely to be a non-native English speaker, Dr Chung. Maybe they'll find it ironic that you botched the sentence after the one where you imply that English isn't my native tongue.

By the way, "rule of thumb" is a rough-and-ready rule that can be applied to a variety of circumstances. Both of the rules of thumb I wrote above fit that description. The latter can apply to the P3C and P2K on a variety of courses and conditions.

It's a shame that you've chosen to hide behind deliberate obtuseness and semantic arguments. I guess if you can't debate the substance of the arguments, these are the means to which you resort.

No class.
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Re: Something borrowed...something FAST! [Frank Day] [ In reply to ]
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Was the thermometer shook down properly after the last temp for instance.

Still stuck in the 1970s? ;)

donm...i can appreciate a healthy dose of cynicism as much as the next person but you have got to let it go. It is pretty apparant that there is a "big" difference between the two frames (your valiant attempts at FUD not withstanding).
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Re: Something borrowed...something FAST! [Andrew Coggan] [ In reply to ]
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So far all you've done is put forth the rather far-fetched hypothesis that, despite setting up the bikes identically, he somehow adopted a position on the P3C that resulted in a significant reduction in drag vs. his well-honed position on the P2k.

Just to clarify, you think that observer expectancy and subject expectancy effects are far-fetched? They do sound far-fetched until you realise how powerful and well-supported by a massive body of literature they are. As both subject and observer in his study, the potential for Tom's expectancy to bias the results is enormous. If you design a study like this, you may find what you expect to find, but it doesn't make it true.

Think outside your engineer box.

As someone who has far more experience in this area than you do, I think that the magnitude of the difference that you're proposing is far-fetched.

Oh, and BTW: I'm a physiologist, not an engineer.
That's good, just fall back on the "trust me, I'm an authority on these matters" argument. After all, we're already trusting Tom not to have introduced any biases to his one-man-band test, so why stop now?
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Re: Something borrowed...something FAST! [OT in CA] [ In reply to ]
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Was the thermometer shook down properly after the last temp for instance.

Still stuck in the 1970s? ;)

donm...i can appreciate a healthy dose of cynicism as much as the next person but you have got to let it go. It is pretty apparant that there is a "big" difference between the two frames (your valiant attempts at FUD not withstanding).
The issue isn't whether I doubt that there is a difference between the frames; I acknowledged that the P3C is likely to be faster than the P3C quite a few pages ago. I just don't think that the method Tom used to produce his results stands much scrutiny.
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Re: Something borrowed...something FAST! [donm] [ In reply to ]
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The rule of thumb that "a delta CdA of X yield a time savings of Ys/km" does not rely on the source(s) of the difference in CdA.

The rule of thumb that "a P3C frame is 2s/km faster than a P2K frame" clearly implies that the frame is the source of the difference in CdA.

I am referring to the latter rule of thumb when I use the term "rule of thumb".

Are we clear?

Perhaps English is not your native tongue, or perhaps you are unfamiliar with the term "rule of thumb." What you're calling a rule of thumb? I don't think it means what you think it means.
I'll leave it to those reading this thread to determine which one of us is the more likely to be a non-native English speaker, Dr Chung. Maybe they'll find it ironic that you botched the sentence after the one where you imply that English isn't my native tongue.

By the way, "rule of thumb" is a rough-and-ready rule that can be applied to a variety of circumstances. Both of the rules of thumb I wrote above fit that description. The latter can apply to the P3C and P2K on a variety of courses and conditions.

It's a shame that you've chosen to hide behind deliberate obtuseness and semantic arguments. I guess if you can't debate the substance of the arguments, these are the means to which you resort.

No class.

Uh-oh. You know up above where you said you were glad to aggravate Andy and me? You sure your skin is thick enough for this? 'Cuz it appears to be time to call the waaaaaaahhmbulance.
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