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Re: Something borrowed...something FAST! [rmur] [ In reply to ]
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other than literally riding blindforded - which is clearly inane - how do you propose to get around this problem?[/reply]
I found that after a sufficient number of field testing runs, I became thoroughly disinterested in what I was riding. I would set up a configuration, jot it down, do the test run, change the configuration, jot it down, do it again, on and on and on. What's more, I was so highly focused on maintaining a constant speed on each run between the entry and exit points, there wasn't much opportunity to think about what I was riding. In this way, I think field-testing was better than the wind-tunnel. It was almost as good as riding blind.


-jens
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Re: Something borrowed...something FAST! [Rappstar] [ In reply to ]
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Dr. Chung.

While you have been "pointing out several facets of Tom's results that suggest that lack of blinding can't explain the magnitude of difference he observed." Here are a couple issues that suggest the opposite.

1. n=1
2. The person who designed the study, was also the subject of the study, also collected the data, and then analyzed the data.

This does not mean that his results are necessarily wrong. But, it does mean that skepticism of the results (especially the interpretation of the results) is not the sign of a weak mind. From a scientific perspective, imho, skepticism is the stronger position.

Isn't this exactly the same thing that goes on with most of the PowerCrank studies (Joaquin comes to mind...)?
Yes and no. Joaquin was not a study, so Joaquin was comparible to this "study", one person gathering the best data he knew how (edit: one difference, he hired a disinterested party, who did this all the time, to test him) to document the benefits of what he was "studying". No one believed him. Yet, the same people who absolutely refused to believe Joaquin's results have accepted Tom's without question.

As regards the PC studies (Luttrell, Dixon), there is no comparison. They all had n's greater than one, had controls, and reached statistical significance regarding what was being studied. While no study is perfect, that is what a scientific study is supposed to do.

--------------
Frank,
An original Ironman and the Inventor of PowerCranks
Last edited by: Frank Day: May 26, 08 22:00
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Re: Something borrowed...something FAST! [Frank Day] [ In reply to ]
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I imagine it would be pretty hard to apply "blindness" to testing the efficacy of clutch based cranks vs regular cranks.
So any such "test" would be biased therefore results would be invalid and we'd be left with trolling through endless anecdotes forever more
:D

_________________________________________________________________________________
Training Plans -- Power Meter Hire -- SRM Sales Australia -- cyclecoach.com -- My Blog -- Sydney Turbo Studio
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Re: Something borrowed...something FAST! [RChung] [ In reply to ]
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But this is what you wrote:
"The subtle changes wouldn't have to be that large to completely invalidate any estimate of time savings over 40k."
"While the lack of blinding may not explain all of the effect, it may explain some. If it does, then any estimate of the magnitude of difference [.] has to be taken with a pinch of salt."
"So how much of a pinch of salt do we need to take it with? Oh that's right, we can't accurately adjust for threats to validity - that's what makes them threats to validity. So we don't actually know with a huge degree of certainty that there was any difference"
I've deleted your incorrect interpretation of my words, but otherwise I stand behind everything that's quoted above.

I'm trying to help you understand the issue with observational, poorly controlled study methods - they produce evidence, but not particularly strong evidence. Evidence provided by scientific research is never definitive as there is ALWAYS a degree of uncertainty associated with it. You always have to look at study results and ask yourself, "have I actually measured what I set out to measure?" Everyone has their own threshold of what constitutes an acceptable level of evidence; yours appears to be lower than mine in this case.

Have I clarified my position, or do I need to read any more posts where you quote me and then put your own little convenient spin on them? Painting me as the, "doesn't understand the nature of uncertainty in science / has totally unrealistic and unreasonable standards of evidence / will never be satisfied by any research that could happen in the real world" straw man is becoming tiresome.

Hmmm. Actually, I think your position has been switching as you've gotten more desperate so I'm all for pressing ahead. I think I'm pretty clear on the issue of poorly controlled study methods. I teach in this area and lecture on this kind of stuff all the time. I tell my students that when they evaluate research they shouldn't stop at pointing out the potential for error. Anyone can do that, and we have a name for it: the "devastating critique," in which actual data-driven research is contrasted with the Platonic Ideal of a study and then dismissed as wanting. (I tell my PhD students that's what MA students do). What makes them worthy of a degree and a future income high in the, um, four figures is the ability to estimate the size of the potential error and figure out a way to tell when the data have been tainted.

The reason why we use blinding is because we're often trying to tease out small effects and we're worried that the bias due to lack of blinding is going to be large relative to those small effects. I've been pointing out several facets of Tom's results that suggest that lack of blinding can't explain the magnitude of difference he observed. You've refused to address that. If you wish to continue this conversation (and I can understand if you do not) then please turn yourself away from the devastating critique and toward the evidence for bias.[/reply] As someone with no experience of aerodynamic testing, I can't estimate the potential error introduced by shifts in body position on a bike set up with similar touch points. What do you think it is? How would you go about estimating it here? Again, I understand research methods but do not claim to be an expert on engineering-specific methods of estimating potential error due to changes in position in aerodynamic testing. I'll leave that to you.

I would agree with your point that, depending on its magnitude, this error probably doesn't invalidate the conclusion that the P3C is a faster frame for Tom. I think I've said that. However, again depending on its magnitude, would it not render these estimates of time savings per km (was it 2 seconds per km?) invalid? Wouldn't they become substantially broader ranges of potential time savings if this potential error is large?

Also, as Frank points out, we're being expected to swallow a whole lot of poor design in this n=1, one-man-band study. Would evidence from a study like this be an acceptable basis for making decisions high in the, um, four figure bracket that you inhabit?

Cheers,
Don

PS - How can I be expected to debate with a man who sends people on their way to income in excess of $9,000? ;)
Last edited by: donm: May 27, 08 0:48
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Re: Something borrowed...something FAST! [Tom A.] [ In reply to ]
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So, in 2007, using the following inputs:

Area = .225 m^2
Cd = 1 (this plus the Area were obviously chosen to make the CdA product the measured .225 m^2)
Air Density = 1.08 kg/m^3
Mass = 84 kg
Crr = .004
Slope = 0
Power = 230W

That results in a predicted speed of 11.64 m/s, for a total time over the 37.1 km course of 53:07

...

Well, the ROT says that should be equivalent to a CdA drop of .022 m^2, which would put my 2008 CdA at .203 m^2. Hmmm...does that number look familiar?? Pretty close to my measured .205 m^2, right?

If I plug a CdA of .205 m^2 into the calculator with my 2008 power it comes up with a speed of 12.08 m/s, which would be a predicted time of 51:11 vs. the 52:40 with a CdA of .225 m^2...or, about 1:30 faster. That's pretty darn close to the 1:22 difference calculated above, huh?

Now...I know the bike was different (Soloist vs. P2K), but measured CdA of the setup I ran last year was within .002 m^2 of what I measured for the P2K, so it's safe to say that I would've been the same speed on either bike. My position (as measured by the location of the "touch points" relative to the BB) was identical.
Hello Tom,

Thanks for the great info and specific calculations.

For me it seems that I can win much more speed by improving my CdA than by increasing my power numbers. How did you become so aero? Total weight bike + you = 84kg? What is your length? I am 69kg and 180cm and we ride the same speed in timetrials but I have to produce much more power. I did 3 timetrials last year and with 315 watts I did them with 41.5-43.0km/hour depending of wind and corners. I hope to increase my power to 350watts, my estimated gain would be 63s (28:22 to 27:19) on a 20km timetrial (11.75m/s to 12.20ms, CdA=0.28, Aird=1.226, Crr=0.004, weight=80kg). But you have a CdA of .225 m^2 and .205 m^2 that would be a much better goal for me because with a CdA of 0.225 and my last years poweroutput (315w) I could do a 20km in 26:29. That's sick fast and almost 2 minutes faster than with a CdA of 0.28. I always tought (till today) that those guys were out of my reach...

In august 2008 I want to do 350 watts for 30 minutes and I want to reduce my CdA to 0.26 m^2 (that's 45km/hour | 26:40 for a 20km) do you guys think a 69kg/180cm person can go to 0.23 m^2 (46.8km/hour | 25:40)?

I ride on a small road frame, fsa basebar+bars with zipp 404 + wheelcover, with skinsuit, giro atmos with cover, shoe covers, pro2race rear tire, zipp front tire and latex innertubes, flat back.

Hmmm, informative topic but maybe a very expensive one for me.
Because when I can buy a CdA of 0.23m^2, ooooh :-) :-) when is the P4C coming, hahaha :-) :-)
Last edited by: Paul_nl: May 27, 08 2:05
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Re: Something borrowed...something FAST! [Frank Day] [ In reply to ]
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Dr. Chung.

While you have been "pointing out several facets of Tom's results that suggest that lack of blinding can't explain the magnitude of difference he observed." Here are a couple issues that suggest the opposite.

1. n=1
2. The person who designed the study, was also the subject of the study, also collected the data, and then analyzed the data.

This does not mean that his results are necessarily wrong. But, it does mean that skepticism of the results (especially the interpretation of the results) is not the sign of a weak mind. From a scientific perspective, imho, skepticism is the stronger position.

Isn't this exactly the same thing that goes on with most of the PowerCrank studies (Joaquin comes to mind...)?
Yes and no. Joaquin was not a study, so Joaquin was comparible to this "study", one person gathering the best data he knew how (edit: one difference, he hired a disinterested party, who did this all the time, to test him) to document the benefits of what he was "studying". No one believed him. Yet, the same people who absolutely refused to believe Joaquin's results have accepted Tom's without question.

As regards the PC studies (Luttrell, Dixon), there is no comparison. They all had n's greater than one, had controls, and reached statistical significance regarding what was being studied. While no study is perfect, that is what a scientific study is supposed to do.
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[Tom.A] ...snipped ... So...what's the bottom line?

Well...taking the same rider, the same wheels, the same basebars and brake levers, and with the seat and extensions adjusted to deliver the same positions...at basically zero yaw conditions I apparently measured a drag difference of ~.023 m^2 of CxA (or Cda, whichever you prefer - .228 m^2 for the P2K and .205 for the P3C). Using Doc C's "rule of thumb", that basically equates to ~2.5s per km of time savings.
attention peanut gallery. Here's what Tom actually concluded/summarized in his introductory post ... now tell me just what's wrong with that (especially the bolded portion)???
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Re: Something borrowed...something FAST! [Alex Simmons] [ In reply to ]
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I imagine it would be pretty hard to apply "blindness" to testing the efficacy of clutch based cranks vs regular cranks.
So any such "test" would be biased therefore results would be invalid and we'd be left with trolling through endless anecdotes forever more
:D
yes it is, essentially impossible, to incorporate "blindness" into a study on PowerCranks, at least as far as the participants go. However, it is possible to blind the evaluator. Such a study is called a single blind study. It is considered superior to a "no one is blinded" study and inferior to a double blinded study. One can only be expected to do the best job one can given the time and money available.

All scientific studies have potential problems. Most major difficulties are not so much in conducitng the study but in interpreting the results, regardless of the study design. For instance, we have had many discussions here regarding the "problems" associated with some of the seminal studies of some of the most respected researchers in the field, e.g., Coyle et. al.

--------------
Frank,
An original Ironman and the Inventor of PowerCranks
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Re: Something borrowed...something FAST! [rmur] [ In reply to ]
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In Reply To:
In Reply To:
In Reply To:
Dr. Chung.

While you have been "pointing out several facets of Tom's results that suggest that lack of blinding can't explain the magnitude of difference he observed." Here are a couple issues that suggest the opposite.

1. n=1
2. The person who designed the study, was also the subject of the study, also collected the data, and then analyzed the data.

This does not mean that his results are necessarily wrong. But, it does mean that skepticism of the results (especially the interpretation of the results) is not the sign of a weak mind. From a scientific perspective, imho, skepticism is the stronger position.

Isn't this exactly the same thing that goes on with most of the PowerCrank studies (Joaquin comes to mind...)?
Yes and no. Joaquin was not a study, so Joaquin was comparible to this "study", one person gathering the best data he knew how (edit: one difference, he hired a disinterested party, who did this all the time, to test him) to document the benefits of what he was "studying". No one believed him. Yet, the same people who absolutely refused to believe Joaquin's results have accepted Tom's without question.

As regards the PC studies (Luttrell, Dixon), there is no comparison. They all had n's greater than one, had controls, and reached statistical significance regarding what was being studied. While no study is perfect, that is what a scientific study is supposed to do.
Quote:
[Tom.A] ...snipped ... So...what's the bottom line?

Well...taking the same rider, the same wheels, the same basebars and brake levers, and with the seat and extensions adjusted to deliver the same positions...at basically zero yaw conditions I apparently measured a drag difference of ~.023 m^2 of CxA (or Cda, whichever you prefer - .228 m^2 for the P2K and .205 for the P3C). Using Doc C's "rule of thumb", that basically equates to ~2.5s per km of time savings.
attention peanut gallery. Here's what Tom actually concluded/summarized in his introductory post ... now tell me just what's wrong with that (especially the bolded portion)???
And, then he goes and attributes all the difference to the frame and everyone blithely accepts the data as representing reality.

I might also point out it seems he actually only achieved about half the time savings he expected based upon his measurements and Doc C's "rule of thumb". And, in line with this observation, his calculated CdA for the TT was .214 (according to Alex Simmons), not the .205 he expected from his testing. Where did this difference come from since he has assured us that it couldn't be him? I know, it is all frame.

--------------
Frank,
An original Ironman and the Inventor of PowerCranks
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Re: Something borrowed...something FAST! [Frank Day] [ In reply to ]
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As regards the PC studies (Luttrell, Dixon), there is no comparison. They all had n's greater than one, had controls, and reached statistical significance regarding what was being studied. While no study is perfect, that is what a scientific study is supposed to do.

Could you describe the controls for the Dixon study, and the hypothesis that was tested?

Could you point to the research -->prior<-- to the Luttrell study that made them think that PCs would affect efficiency?
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Re: Something borrowed...something FAST! [chewgl] [ In reply to ]
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[/quote] http://en.wikipedia.org/wiki/Hour_record

Check out the hour records (note that they are in distance traveled, not time taken). Aero equipment and position *does* make a difference. Ummm, duh, i never said it didn't! I guestimated the time difference, and thanks to your link it's pretty accurate.
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[/quote] Do you race? Like in USA Cycling road races? Do you notice that the best bikes out there are not ridden by the professionals in the Pro/1/2 races, but by the Cat 4s and 5s?

The P3c is an expensive bike, as are many of the better TT bikes out there. Normal people (i.e. not sponsored people) who have the money to buy a P3C-like bike probably don't have enough time to train on it. You simply can't compare sales with wins... there are too many variables in between. Again, read my other posts, comparing anything other than the top pro's is pointless due to all the variables (although that still favors against Cervelo, add it up some time). I'm only talking top pro's who are the best of the best, riding the best of the best equipment. P3C results do not match the number of riders on them, plain and simple, do the math!
In Reply To:
[/quote]
"obviously extremely close to each other in ability". Really??
I don't understand your "real world research". If you're basing everything off the assumption that all the pro cyclists and triathletes are of similar ability, you might have an argument there. But they do not have similar ability... some riders are better at climbing, some better at time trialing, some better at sprinting. Some are team leaders, some are domestiques. Some aim for the spring classics, some aim for the grand tours. The range in their abilities are large enough that they exceed the advantage a bike can provide (look at the margins the Tour de France, or the Ironman world championships are won by, like amongst the top 10, top 20 etc). CSC having a huge advantage? They do... and they've something to show for it: they've won the UCI protour team rankings for 3 years in a row. Some of it can be attributed to the bikes they ride, but some of it has to be other factors.

To be continued... i've got better things to do in the meantime... Again, you're missing the point.....try comparing apples to apples. In a Tour TT (prologue/middle/last TT), as in the results I have provided, these are the best of the best TT riders. Guys riding P3C's DO NOT dominate, not even close compared to the ratio of riders on them. Again, P3C riders DO NOT dominate at triathlon either. My point is, Cervelo is a great bike (I've owned 4 of them and still do). However, the "two minute rule" is missing out in the real life (ie top tier pro) applications.......
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Re: Something borrowed...something FAST! [donm] [ In reply to ]
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As someone with no experience of aerodynamic testing

As someone with some experience in this area, I'd say that's obvious from your comments. ;-)

In Reply To:
I would agree with your point that, depending on its magnitude, this error probably doesn't invalidate the conclusion that the P3C is a faster frame for Tom. I think I've said that. However, again depending on its magnitude, would it not render these estimates of time savings per km (was it 2 seconds per km?) invalid? Wouldn't they become substantially broader ranges of potential time savings if this potential error is large?

As has been repeatedly stated in this thread, the difference observed is an order of magnitude greater than the experimental error. 'nuff said.
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Re: Something borrowed...something FAST! [Frank Day] [ In reply to ]
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I might also point out it seems he actually only achieved about half the time savings he expected based upon his measurements and Doc C's "rule of thumb". And, in line with this observation, his calculated CdA for the TT was .214 (according to Alex Simmons), not the .205 he expected from his testing. Where did this difference come from

You're ignoring the fact that Tom made the conservative assumption that the wind was no worse this year than last year.
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Re: Something borrowed...something FAST! [RChung] [ In reply to ]
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What makes them worthy of a degree and a future income high in the, um, four figures

Sigh...I need to change fields.
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Re: Something borrowed...something FAST! [donm] [ In reply to ]
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As someone with no experience of aerodynamic testing, I can't estimate the potential error introduced by shifts in body position on a bike set up with similar touch points. What do you think it is? How would you go about estimating it here? Again, I understand research methods but do not claim to be an expert on engineering-specific methods of estimating potential error due to changes in position in aerodynamic testing. I'll leave that to you.


That's actually two questions: first, how much potential error could be introduced by shifts in body position; second, how detectable would those changes be?

Once the main touch points are fixed, the remaining thing to worry about is head position. However, this was not a one-off aero test. Tom has about as much experience with this particular method as anyone (certainly more than I). Tom has worked on his position quite a bit which is evident by his ability to repeat his CdA on his reference frame to about 1%. Since his estimated CdA in this test matches his estimated CdA from other tests, we know he wasn't sitting up in order to make the P2K look bad. This is going to put a floor, not a ceiling on his positional CdA. In that case, small changes in head position will affect variance of the estimate, not its location. In this method, precision and location estimation are separable. Parameter location is determined by the tilt of the profiles; good precision produces lap profiles that look identical, while poor precision distorts the lap profiles. I don't have the data, only the lap profiles from the plots, but I'd say the precision of the P3C laps is only slightly larger than for the P2K laps.


I would agree with your point that, depending on its magnitude, this error probably doesn't invalidate the conclusion that the P3C is a faster frame for Tom. I think I've said that. However, again depending on its magnitude, would it not render these estimates of time savings per km (was it 2 seconds per km?) invalid? Wouldn't they become substantially broader ranges of potential time savings if this potential error is large?

The 2 s/km is a rule of thumb, but if you want you can go to analyticcycling.com, put in Tom's parameters and make an exact calculation of how much a delta CdA of .023 m^2 would mean. At normal air density and with Tom's average power, we're talking around 2 - 2.5 s/km. The value of this exercise is that you can play with analyticcycling and see how much a decrease of 5%, 10%, 15%, or 20% in the delta CdA would mean.


Also, as Frank points out, we're being expected to swallow a whole lot of poor design in this n=1, one-man-band study. Would evidence from a study like this be an acceptable basis for making decisions high in the, um, four figure bracket that you inhabit?

Cheers,
Don

PS - How can I be expected to debate with a man who sends people on their way to income in excess of $9,000? ;)
[/reply]
Frank really isn't the person to be leaning on when making judgments about good or poor study design. I tell the PhD students that doctorates rarely pay off in terms of income, when discounted to PV. That's just truth in advertising. As an aside, Frank really isn't the go-to guy on that one, either.
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Re: Something borrowed...something FAST! [jens] [ In reply to ]
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other than literally riding blindforded - which is clearly inane - how do you propose to get around this problem?

I found that after a sufficient number of field testing runs, I became thoroughly disinterested in what I was riding. I would set up a configuration, jot it down, do the test run, change the configuration, jot it down, do it again, on and on and on. What's more, I was so highly focused on maintaining a constant speed on each run between the entry and exit points, there wasn't much opportunity to think about what I was riding. In this way, I think field-testing was better than the wind-tunnel. It was almost as good as riding blind.


-jens[/reply]good point Jens. The fun is in analyzing the data - not collecting it! That's a pretty hum-drum tedious process .... necessary but boring .
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Re: Something borrowed...something FAST! [jens] [ In reply to ]
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other than literally riding blindforded - which is clearly inane - how do you propose to get around this problem?

I found that after a sufficient number of field testing runs, I became thoroughly disinterested in what I was riding. I would set up a configuration, jot it down, do the test run, change the configuration, jot it down, do it again, on and on and on. What's more, I was so highly focused on maintaining a constant speed on each run between the entry and exit points, there wasn't much opportunity to think about what I was riding. In this way, I think field-testing was better than the wind-tunnel. It was almost as good as riding blind.


-jens[/reply]
Hi Jens!

What you point out is something that makes me "chuckle" when I read people complaining about the measurements not being "blinded". In your case, you were doing your testing at a constant speed. Despite, as you say, needing to concentrate on a keeping your speed constant, you still could get some sense of whether or not a particular piece of equipment is slower or faster just by taking a quick peek at the power reading.

However, when doing it "Chung-style", the idea is to not worry about holding a constant speed, but to actually vary the speed over the laps. There's absolutely NO WAY I can tell while I'm riding if a particular setup is "fast" or "slow". First off, the changes being measured are way too subtle for me to be able to "feel" them, and second, the wildly varying speed/power relationship during the run is useless for determining any "in situ" estimates of differences. I basically ignore the PM computer during the runs and spend my "concentration tickets" on maintaining my position and following a consistent line around the course.

In a sense, the results are "blinded" to me since I have no way of determining what is "fast" or "slow" until AFTER the entire session is over and I download the data and process it.

I've commented before that a few times my "perceptions" of what was faster was totally the opposite of what actually was faster. In this case, as I related earlier, if I had to choose which setup "felt" faster...I'd have chosen the P2K. This also happened to me when I was testing Crr vs. tire pressure. Pressures above ~120 psi "felt" fast...but they weren't.

I'm still trying to figure out how I can "will" the power meter to record lower or higher power than it actually takes... ;-)

http://bikeblather.blogspot.com/
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Re: Something borrowed...something FAST! [Paul_nl] [ In reply to ]
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So, in 2007, using the following inputs:

Area = .225 m^2
Cd = 1 (this plus the Area were obviously chosen to make the CdA product the measured .225 m^2)
Air Density = 1.08 kg/m^3
Mass = 84 kg
Crr = .004
Slope = 0
Power = 230W

That results in a predicted speed of 11.64 m/s, for a total time over the 37.1 km course of 53:07

...

Well, the ROT says that should be equivalent to a CdA drop of .022 m^2, which would put my 2008 CdA at .203 m^2. Hmmm...does that number look familiar?? Pretty close to my measured .205 m^2, right?

If I plug a CdA of .205 m^2 into the calculator with my 2008 power it comes up with a speed of 12.08 m/s, which would be a predicted time of 51:11 vs. the 52:40 with a CdA of .225 m^2...or, about 1:30 faster. That's pretty darn close to the 1:22 difference calculated above, huh?

Now...I know the bike was different (Soloist vs. P2K), but measured CdA of the setup I ran last year was within .002 m^2 of what I measured for the P2K, so it's safe to say that I would've been the same speed on either bike. My position (as measured by the location of the "touch points" relative to the BB) was identical.
Hello Tom,

Thanks for the great info and specific calculations.

For me it seems that I can win much more speed by improving my CdA than by increasing my power numbers. How did you become so aero? Total weight bike + you = 84kg? What is your length? I am 69kg and 180cm and we ride the same speed in timetrials but I have to produce much more power. I did 3 timetrials last year and with 315 watts I did them with 41.5-43.0km/hour depending of wind and corners. I hope to increase my power to 350watts, my estimated gain would be 63s (28:22 to 27:19) on a 20km timetrial (11.75m/s to 12.20ms, CdA=0.28, Aird=1.226, Crr=0.004, weight=80kg). But you have a CdA of .225 m^2 and .205 m^2 that would be a much better goal for me because with a CdA of 0.225 and my last years poweroutput (315w) I could do a 20km in 26:29. That's sick fast and almost 2 minutes faster than with a CdA of 0.28. I always tought (till today) that those guys were out of my reach...

In august 2008 I want to do 350 watts for 30 minutes and I want to reduce my CdA to 0.26 m^2 (that's 45km/hour | 26:40 for a 20km) do you guys think a 69kg/180cm person can go to 0.23 m^2 (46.8km/hour | 25:40)?

I ride on a small road frame, fsa basebar+bars with zipp 404 + wheelcover, with skinsuit, giro atmos with cover, shoe covers, pro2race rear tire, zipp front tire and latex innertubes, flat back.

Hmmm, informative topic but maybe a very expensive one for me.
Because when I can buy a CdA of 0.23m^2, ooooh :-) :-) when is the P4C coming, hahaha :-) :-)

We are basically the same size....and about 4 years ago I had ~the same CdA you are quoting. Looking back at some of my performances then, I'd guesstimate my CdA at being in the .275-.280 range on a steel round tubed frame.

The majority of improvements, obviously, have come about with changes and "tweaks" to body position. The .225 number was accomplished on a road bike, albeit a very aero road bike, i.e. an aluminum Soloist, that was set up "TT style" with a dedicated TT bar front end and an ergostem to get the bars low enough.

My main suggestion would be to first, if you don't already have one, get a power meter. Then, use that as described in the first post in this thread as a tool in investigating what works for you. It just takes a lot of time, patience, and curiousity...that's all ;-)

Oh yeah...trade in that Atmos for an aero helmet...

I hope that helps.
Tom

http://bikeblather.blogspot.com/
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Re: Something borrowed...something FAST! [Tom A.] [ In reply to ]
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I'm still trying to figure out how I can "will" the power meter to record lower or higher power than it actually takes... ;-)

Perhaps Frank and/or Joaquin could help you out with that issue.
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Re: Something borrowed...something FAST! [sib1] [ In reply to ]
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[/quote] http://en.wikipedia.org/wiki/Hour_record

Check out the hour records (note that they are in distance traveled, not time taken). Aero equipment and position *does* make a difference. Ummm, duh, i never said it didn't! I guestimated the time difference, and thanks to your link it's pretty accurate.
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[/quote] Do you race? Like in USA Cycling road races? Do you notice that the best bikes out there are not ridden by the professionals in the Pro/1/2 races, but by the Cat 4s and 5s?

The P3c is an expensive bike, as are many of the better TT bikes out there. Normal people (i.e. not sponsored people) who have the money to buy a P3C-like bike probably don't have enough time to train on it. You simply can't compare sales with wins... there are too many variables in between. Again, read my other posts, comparing anything other than the top pro's is pointless due to all the variables (although that still favors against Cervelo, add it up some time). I'm only talking top pro's who are the best of the best, riding the best of the best equipment. P3C results do not match the number of riders on them, plain and simple, do the math!
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[/quote]
"obviously extremely close to each other in ability". Really??
I don't understand your "real world research". If you're basing everything off the assumption that all the pro cyclists and triathletes are of similar ability, you might have an argument there. But they do not have similar ability... some riders are better at climbing, some better at time trialing, some better at sprinting. Some are team leaders, some are domestiques. Some aim for the spring classics, some aim for the grand tours. The range in their abilities are large enough that they exceed the advantage a bike can provide (look at the margins the Tour de France, or the Ironman world championships are won by, like amongst the top 10, top 20 etc). CSC having a huge advantage? They do... and they've something to show for it: they've won the UCI protour team rankings for 3 years in a row. Some of it can be attributed to the bikes they ride, but some of it has to be other factors.

To be continued... i've got better things to do in the meantime... Again, you're missing the point.....try comparing apples to apples. In a Tour TT (prologue/middle/last TT), as in the results I have provided, these are the best of the best TT riders. Guys riding P3C's DO NOT dominate, not even close compared to the ratio of riders on them. Again, P3C riders DO NOT dominate at triathlon either. My point is, Cervelo is a great bike (I've owned 4 of them and still do). However, the "two minute rule" is missing out in the real life (ie top tier pro) applications.......

The main points you seem to keep glossing over are:

1. The P3C isn't the ONLY bike frame in it's "aero class". The Trek TTX and Felt DA have been revealed to be "neck and neck" with it.
2. You assume that the positions for each rider have been optimized. A bad position and/or equipment choices on a P3C (or TTX, or DA) can "swamp" any potential gains from the frames as compared to rider's on bikes not listed in #1 above.
3. The riders all have the same power outputs.

You can't compare rider to rider in this type of analysis...you can only compare a particular rider to what he would have done otherwise....there's a difference.

http://bikeblather.blogspot.com/
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Re: Something borrowed...something FAST! [Tom A.] [ In reply to ]
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[/reply]
The main points you seem to keep glossing over are:

1. The P3C isn't the ONLY bike frame in it's "aero class". The Trek TTX and Felt DA have been revealed to be "neck and neck" with it.
2. You assume that the positions for each rider have been optimized. A bad position and/or equipment choices on a P3C (or TTX, or DA) can "swamp" any potential gains from the frames as compared to rider's on bikes not listed in #1 above.
3. The riders all have the same power outputs.

You can't compare rider to rider in this type of analysis...you can only compare a particular rider to what he would have done otherwise....there's a difference.[/reply]
agreed, and i'll bug out of this so i can actually get some work done......i don't think there's any one great and totally accurate way to compare it across the board, i guess that's my main point (opinion). if you guys think it's perfectly accurate then that's up to you. for you personally i think it's a cool study
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Re: Something borrowed...something FAST! [Tom A.] [ In reply to ]
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in 2007, using the following inputs:

Area = .225 m^2
Cd = 1 (this plus the Area were obviously chosen to make the CdA product the measured .225 m^2)
Air Density = 1.08 kg/m^3
Mass = 84 kg
Crr = .004
Slope = 0
Power = 230W

That results in a predicted speed of 11.64 m/s, for a total time over the 37.1 km course of 53:07

Now, in 2008, the temperature was 20F lower and the barometric pressure was higher, which resulted in the air density increasing to 1.124 kg/m^3. Another temperature effect is on the Crr. A commonly accepted compensation for temp is 0.6%/deg F. This means the Crr would increase to .0045 from .004.

So what sort of time would you predict for 2008 for someone with an all-up mass of 75 kg, a CdA of 0.200 m^2, and a power of 290 W? ;-)
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Re: Something borrowed...something FAST! [eb] [ In reply to ]
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Another big question is how the ibike responds to yaw. The makers say they've never tested it.

Seriously? I would have thought that they'd have put significant effort into ensuring that the shape of the port was such that the readings were as independent of yaw angle as possible.
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Re: Something borrowed...something FAST! [sib1] [ In reply to ]
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"I guestimated..."

That's the problem with your whole argument, sib1. You're talking about guesses and what you "think" sounds right. These guys are talking actual measured numbers. Your argument is emotional based. Theirs is fact based. You can argue the computations and addition or subtraction of variables...but the measurements are facts.

In fact all of the people in this thread who take issue with Tom's assessment are doing so without actually going through the math and analysis of Chung's method. You all have offered ways that the numbers might be lacking or that some sort of "bias" has been induced...without actually running the computations and looking at the results.

You all may be on to something...or you may not... but in terms of debate...you are all losing...HORRIBLY. Sib's "what the pros do" is a strawman argument that lends NOTHING to the debate. In using that argument, Sib, you are trying to have things both ways...controlled...AND uncontrolled. Without breaking pro results down to individual efforts and controlling for the variables (as in what Tom and others have done here), your argument is too broad to actually lend support to your contention that the frame doesn't matter.

Bring the numbers and computations to support your statements.
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Re: Something borrowed...something FAST! [Andrew Coggan] [ In reply to ]
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In Reply To:
In Reply To:
in 2007, using the following inputs:

Area = .225 m^2
Cd = 1 (this plus the Area were obviously chosen to make the CdA product the measured .225 m^2)
Air Density = 1.08 kg/m^3
Mass = 84 kg
Crr = .004
Slope = 0
Power = 230W

That results in a predicted speed of 11.64 m/s, for a total time over the 37.1 km course of 53:07

Now, in 2008, the temperature was 20F lower and the barometric pressure was higher, which resulted in the air density increasing to 1.124 kg/m^3. Another temperature effect is on the Crr. A commonly accepted compensation for temp is 0.6%/deg F. This means the Crr would increase to .0045 from .004.

So what sort of time would you predict for 2008 for someone with an all-up mass of 75 kg, a CdA of 0.200 m^2, and a power of 290 W? ;-)

I'm guessing about 50:00 even...give or take some seconds either way ;-)

edit: The crazy thing is...a time that fast still wouldn't have won the Cat 4s, nor the Masters 45-49. Rough crowd out here, huh?

http://bikeblather.blogspot.com/
Last edited by: Tom A.: May 27, 08 9:56
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Re: Something borrowed...something FAST! [Tom A.] [ In reply to ]
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In Reply To:
In Reply To:
In Reply To:
in 2007, using the following inputs:

Area = .225 m^2
Cd = 1 (this plus the Area were obviously chosen to make the CdA product the measured .225 m^2)
Air Density = 1.08 kg/m^3
Mass = 84 kg
Crr = .004
Slope = 0
Power = 230W

That results in a predicted speed of 11.64 m/s, for a total time over the 37.1 km course of 53:07

Now, in 2008, the temperature was 20F lower and the barometric pressure was higher, which resulted in the air density increasing to 1.124 kg/m^3. Another temperature effect is on the Crr. A commonly accepted compensation for temp is 0.6%/deg F. This means the Crr would increase to .0045 from .004.

So what sort of time would you predict for 2008 for someone with an all-up mass of 75 kg, a CdA of 0.200 m^2, and a power of 290 W? ;-)

I'm guessing about 50:00 even...give or take some seconds either way ;-)
Give or take. ;-)
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