[/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] your attempts at sarcasm are interesting, but i think you're missing my point. i'm talking about the geometries of the bikes, not the tube shapes etc. no doubt the P3C tube shapes are likely faster, but i'm talking about tube lengths etc. so you think if the P3C's tubes were 50m long they'd still be faster than the P2K's just bc they're better shaped?

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[/reply] I wouldn't even agree that one can achieve the "same" body position. One can achieve "similar body positions". but the same (identical) position, no way. How much the shoulders sag, the neck sags, the finger positioning, are all going to vary from ride to ride and even during the same ride. It is my understanding that wind tunnel testing has shown that very small differences in body position can have quite large influences on drag, both positively and negatively. Even though attempts were made to keep body position similar, it is impossible to know that they are. It simply is not reasonable to attribute all these aerodynamic changes to the bicycle frame alone.

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Frank,
An original Ironman and the Inventor of PowerCranks

again please RTFM over and over until you can recite it by chapter and verse. The quiz will be on Monday .. But to make one point, each trial is effectively multiple trials (laps) and us visual monkeys are darned good at picking out patterns that match (or do not!). Something about the jungle I suppose ... So while I did query the magnitude of the delta, the noise ain't nearly as bad you suggest. Repeatability is ~0.001 m^2 or ~1W. Yes, that implies the PM is repeatable to around 1W. I have about five million step tests vs. my PT Pro and CT and two million with my SRM and CT from 150 to 450W and they show the same thing. Repeatability is considerably better than the stated accuracy. I have no problem with that ... Anyhow, carry on ...

[/reply] I wouldn't even agree that one can achieve the "same" body position. One can achieve "similar body positions". but the same (identical) position, no way. How much the shoulders sag, the neck sags, the finger positioning, are all going to vary from ride to ride and even during the same ride. It is my understanding that wind tunnel testing has shown that very small differences in body position can have quite large influences on drag, both positively and negatively. Even though attempts were made to keep body position similar, it is impossible to know that they are. It simply is not reasonable to attribute all these aerodynamic changes to the bicycle frame alone.[/reply]
again i agree.......when Cobb talks about a long drink straw being much less aero than a short one or cables being very non-aero etc, you know tiny changes make the difference. there is no way a human could completely accurately have the exact same overall position, nor can you tell me tube dimensions, materials, etc don't play a factor.

i'm not knocking Tom at all for doing this, it is pretty interesting, just saying it's no rule of thumb

I will accept your assessment of the accuracy of this result. Do you believe it is correct to assign all the change seen to the bicycle?

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Frank,
An original Ironman and the Inventor of PowerCranks

Being out on the bike, on the road, pedalling, behaving as if you are racing - isn't real world?

[/reply]
Being out on the bike, on the road, pedalling, behaving as if you are racing - isn't real world?[/reply]
pretending like a human is able to hold the same exact position on any different bike, or even the same bike in multiple trials, is not real world.

a mannequin in a wind tunnel might be a different story....but obviously that's not real world either. in the real world guys go very similar times regardless of frame choice (within reason)

maybe if we were talking P3C over a round tube bike, but not over a bike that already has very aero shaped tubes

How? As others have said, by putting my touchpoints in the exact same position relative to the BB on both bikes. Not only was it X/Y dimensions (as looking from the side), "stack and reach" to the saddle, pads, and end of the bars...but it was also pad width and extension width as well.

I did the exact same thing I'd do if I was setting up a brand new bike for myself. Why would I change my body position just because some of the frame dimensions are slightly different? That would be bass-ackwards.

I'm not following how the frame geometry dimensions could be "way better or way worse"...in what way?

As to the validity of the test, both of these frames are the size I'd buy if I were to acquire either of them brand new. Isn't that a more "apples to apples" test (i.e the frame sizes a single person would use) as opposed to comparing 2 sizes that a manufacturer happens to label a particular number?

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http://bikeblather.blogspot.com/

It's really not hard to set the bike components to be in exactly comparable locations to make it as easy as possible to hold position. Also note what Tom has said about repeatability of results during sessions.

Notice that Rik Keller got a 30s improvement out of a frame change. I had a 40s improvement from one aero frame to the next over 10mi and my predicted times using methods related to the one in this thread are usually within 1W of actual power.

[/reply]
It's really not hard to set the bike components to be in exactly comparable locations to make it as easy as possible to hold position. Also note what Tom has said about repeatability of results during sessions.

Notice that Rik Keller got a 30s improvement out of a frame change. I had a 40s improvement from one aero frame to the next over 10mi and my predicted times using methods related to the one in this thread are usually within 1W of actual power.[/reply]
right, and it's also possible you could be faster changing from a P3C to a P2K with the same perceived held position. a different frame and it's shapes/sizes etc are going to effect everyone differently. just like a bottle on the seat tube effects every bike differently, even if it's in the exact same place

.023 m^2 worth of subtle improvements? Yow.

The subtle changes wouldn't have to be that large to completely invalidate any estimate of time savings over 40k. We may be able to say with a reasonable degree of confidence that one frame is faster than the other, but not by how much.

Apparently engineers and bike researchers aren't very familiar with placebo effects.

Then in what world is Tom reproducing CdAs to within .002 m^2 on the same bike in multiple trials? The difference he's measuring between the P2K and P3C is an order of magnitude larger than that.

Well, that's a pretty bold statement. So if the subtle changes don't need to be that large, just how large would they need to be in order to "completely invalidate any estimate of time savings over 40K"?

Are you going to provide some evidence for this assertion?

How do you know your body position is "identical", and how confident are you that you're "definitely not slower"? Did you compare the two frames in the wind tunnel? Did you conduct rigorous field testing with both bikes?

Please provide evidence similar to what Tom and Rik have provided in support of their bike-to-bike comparisons.

Please explain what you mean by "real-world example", since what you've provided so far is simply an unsupported belief-based assertion.

Thanks in advance,

Eric

 
Please explain what you mean by "real-world example", since what you've provided so far is simply an unsupported belief-based assertion.[/reply]
i think the most obvious example is the fact that, if an "extremely good" frame like the P3C is 2 minutes faster in 40k or 10 minutes over Ironman (which is huge) over a "very good" frame like the P2K, then do a little real world research on pro cyclists and pro triathletes. these guys are obviously extremely close to each other in ability, and a frame that much faster would make Cervelo riders win the majority of the time (relative to the number of guys on them), which they clearly don't. CSC would have a huge advantage over other teams and dominate the time trials several deep, which they don't. a pro triathlete would have a 10 minute advantage supposedly at Hawaii, which means the Cervelo rider has a huge advantage and far more likely to win, which they don't.

science is great, but it doesn't always apply to the real world, argue it all day but it's still not yet happened.....

Ain't that the truth. I'm glad you pointed out all these inconsistencies with Tom A's testing, this is what is great about Slowtwitch!

i think the most obvious example is the fact that, if an "extremely good" frame like the P3C is 2 minutes faster in 40k or 10 minutes over Ironman (which is huge) over a "very good" frame like the P2K, then do a little real world research on pro cyclists and pro triathletes. these guys are obviously extremely close to each other in ability, and a frame that much faster would make Cervelo riders win the majority of the time (relative to the number of guys on them), which they clearly don't. CSC would have a huge advantage over other teams and dominate the time trials several deep, which they don't. a pro triathlete would have a 10 minute advantage supposedly at Hawaii, which means the Cervelo rider has a huge advantage and far more likely to win, which they don't.

science is great, but it doesn't always apply to the real world, argue it all day but it's still not yet happened.....[/reply]
Using Ironman bike splits always seems problematic to me...if one can go a competitive speed at a lower effort, why would they go faster when they could just save more for the run?

Second, it seems to me that CSC has to go against other teams that are using bikes like the TTX or the Felt DA...although when the P3C first came out, I do recall CSC riders winning a fair share of TTs....hmmmm....

Listen, just because a frame is "fast" doesn't mean the bike+rider will be "fast". They'll be fast(er) than they would be otherwise (all things being equal)...but, believe me, there are plenty of ways to go slow even when using a "fast" frame. Tufos anyone? ;-)

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I wouldn't call turtling, shrugging, etc. subtle...those actions are demonstrably measureable. Whether or not his position was "exactly" the same is a large part of the equation, and one that has been glossed over. Short of having a video of him in action at different places during the different runs with markers on, one can only conjecture that his position was "exactly" the same. "Exactly" leaves no room for any difference in his position from one run to the next whatsoever. I think that is what Sib is trying to get at. I have no doubt given Tom A.'s approach and abilities, that if anyone was going to get an exceedlingly similar position, it would be him; but "exact", no.

I wouldn't call turtling, shrugging, etc. subtle...those actions are demonstrably measureable. Whether or not his position was "exactly" the same is a large part of the equation, and one that has been glossed over. Short of having a video of him in action at different places during the different runs with markers on, one can only conjecture that his position was "exactly" the same. "Exactly" leaves no room for any difference in his position from one run to the next whatsoever. I think that is what Sib is trying to get at. I have no doubt given Tom A.'s approach and abilities, that if anyone was going to get an exceedlingly similar position, it would be him; but "exact", no.[/reply]First, I agree "exact" is a hard pill to swallow but in many previous trials Tom has shown repeatability in his CdA estimates to within .002 m^2 so perhaps we can agree to discuss "exact" within that context. In addition, I absolutely agree that turtling and shrugging can produce measurable differences. However:

1. Tom has spent a pretty long time optimizing his position on his P2K.
2. The estimated CdA for his P2K run was similar to the CdA he estimated for an actual TT, so it's not like he pulled a new position out of his hat that left a lot to be optimized.
3. You'd have to assume that shrugging and turtling when he was trying purposefully to hold his position constant would result not in an increased CdA but rather a decreased CdA from what was thought to be an optimized position.
4. He couldn't have been doing the shrugging and turtling for only a short while, he'd had to have held the shrugged turtled position constant during the 6 km long trial run or else the P3C elevation profile would have been distorted compared to the P2K profile; and
5. You'd have to be arguing he did this shrugging and turtling subconsciously, and it resulted in a decrease in CdA an order of magnitude larger than his normal precision.
   

I'm skeptical.

First, I agree "exact" is a hard pill to swallow but in many previous trials Tom has shown repeatability in his CdA estimates to within .002 m^2 so perhaps we can agree to discuss "exact" within that context. In addition, I absolutely agree that turtling and shrugging can produce measurable differences. However:

1. Tom has spent a pretty long time optimizing his position on his P2K.
2. The estimated CdA for his P2K run was similar to the CdA he estimated for an actual TT, so it's not like he pulled a new position out of his hat that left a lot to be optimized.
3. You'd have to assume that shrugging and turtling when he was trying purposefully to hold his position constant would result not in an increased CdA but rather a decreased CdA from what was thought to be an optimized position.
4. He couldn't have been doing the shrugging and turtling for only a short while, he'd had to have held the shrugged turtled position constant during the 6 km long trial run or else the P3C elevation profile would have been distorted compared to the P2K profile; and
5. You'd have to be arguing he did this shrugging and turtling subconsciously, and it resulted in a decrease in CdA an order of magnitude larger than his normal precision.
   

I'm skeptical.[/reply] Just as I am skeptical that the entire improvement he noted is due simply to a different frame when the trials were not blinded (did he have an expectation that one would be better than the other) to either what he was riding or what he was evaluating.

The real "proof" of something being wrong is simply the frame is just not that much better than the competition in real world racing. It is laughable to think that someone at Kona would deliberately give up 8 or more minutes on the bike that would otherwise be "free", thinking that they could "make it up on the run". In 2006 C Ogden had the fastest bike split at IM Canada on what I believe was a P2 variety. How much faster would he have been on a P3 for the same effort? Not 8 minutes I suspect.

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Frank,
An original Ironman and the Inventor of PowerCranks

Hmmm...so the "real proof" that a measurement done under as controlled conditions as possible outside of a wind tunnel is wrong is simply that it doesn't jibe with a completely uncontrolled anecdote??

Ummm....OK....

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http://bikeblather.blogspot.com/