Umm...are you comparing a P2C to a P3C? According to Cervelo's own data, those 2 only vary by ~20 grams or so...or the equivalent of ~.002 m^2 of CdA. Make sense since the entire front triangle is identically shaped.

I was comparing a P2K to the P3C...which is obviously NOT a P2C...and the difference between it and a P3C is an order of magnitude greater.

Sorry...Ogden only possibly could've been faster (all other things being equal...you keep forgetting that part when using these anecdotes) by about 45s if on a P3C.

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http://bikeblather.blogspot.com/

What completely uncontrolled anecdote? Show me some race statistics that even suggest that the P3C can take 2 minutes off a 40k TT or 8 minutes off an IM bike split, on average, especially at the pointy end of the speed range which is where you are at, correct? We should see even greater time improvements in the slower folks, right? It is not like no one has ever raced on the frame such that there is no data. Where are all the improvements that your data suggests should be easy to achieve? That is the problem that suggests there is something wrong with the interpretation of these results that attributes all the improvement you measured to the frame (assuming the improvement you measured to be real).

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Frank,
An original Ironman and the Inventor of PowerCranks

Order of magnitude greater of what? Order of magnitude is a mathematical term. It doesn't seem to apply here unless you have some numbers.

I know nothing of the nuances of these bicycle frames. I thought a P2 would be similar whether made of carbon, aluminum, or straw. It is of little importance. I doubt Cervelo was marketing a bike that they deliberately made slow and there seems to be little difference in speed at the pointy end of the race with regards to bicycle brands or models. Speed seems more consistent with regards to the engine than the bike.

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Frank,
An original Ironman and the Inventor of PowerCranks

[/reply]
Hmmm...so, what you're saying is; for a given position, one of the frames might measure faster than the other because of it's "form"...got it. Ummm...isn't that what I first reported?

BTW, relative to the BB, the seats were in identical positions, so I'm not seeing your "seat more fore/aft" point. Also, I've seen evidence that raising or lowering the body relative to the ground doesn't appreciably change the drag...definitely NOT on the order of .023 m^2 or more.

I find it rather humorous that people point at wind tunnel tests of bikes without riders and say "That's not valid...you need to have a rider on it", and then when someone produces numbers comparing frames using the same rider in the same position and the same wheels some people then say "That's not valid...the rider is too much of a variable on it."

I guess measuring this stuff and making decisions based on it is just plain impossible <rolleyes>[/reply]
right, but it implies the frame is faster, rather than the "the frame for Tom is faster". the amount of seatpost height for a given rider is different on both frames. the seat fore/aft does make a difference because your butt etc is in a different position relative to the seatpost etc etc. and even if rider height above ground doesn't appreciably change the total, all these sums of parts certainly could/would.

like you said in the last line, the reality is i don't think there is a perfectly repeatable method for all persons, or even one person unfortunately. i guess in one way makes it more of a crapshoot and makes the sport more interesting, if there was hard obvious evidence one way or the other pretty much every guy out there would be on the same bike setup!

Here is what Courtney rode in Canada:

It looks little like the current P2C advertised on the Cervelo site. http://www.cervelo.com/bikes.aspx?bike=P2C2008 or a P3C to my eyes.

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Frank,
An original Ironman and the Inventor of PowerCranks

Well...you better get them checked, 'cuz that's a P2K. So yeah, all other things being equal (including the PCs), he could've been ~8 minutes faster...who knows, maybe even faster if he ditched those heavy cranks.

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http://bikeblather.blogspot.com/

.002 m^2 vs. .023 m^2....please try to keep up.



That's OK, it's not the only thing you "know nothing of the nuances of" in this thread...

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http://bikeblather.blogspot.com/

Well...what an interesting coincidence then that "the frame was for Andy is faster" and the "the frame was for Angie is faster" by basically an identical amount, huh?

And their frames are different sizes than the ones I compared. Pretty amazing.

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http://bikeblather.blogspot.com/

I guess you've already forgotten Rik's "race statistics" he presented right here in this thread.

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http://bikeblather.blogspot.com/

I would guess more than ~8mins if the friggin athlete stayed in the goddamed aerobars!!!



any comparison to tt and ironman racing isn't a anywhere near appropriate as it is a mass start race. the tactics are entirely different and effected by the triathletes knowledge of other others in all THREE disiplines.

as I learned growing up, finish a tt with nothing left ten feet from the finish line. if ironman races were run on random (ability and order) staggered starts, you might see dramatically different results... I will leave the comments about that to the rappstars here that have personal experince.

g

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greg
www.wattagetraining.com

Being skeptical is not surprising. I'm agog over the magnitude of this difference, too. However, when you keep harking back to blinding when 1) blinding isn't possible in this sort of test and 2) the lack of blinding can't (for reasons I've just listed and you just copied) explain the size of this effect, then you're moving out of skepticism and over toward denial. [Smacking self on head] Wait! Doh! I'm talking to Frank Day. Of course you're in denial.

C'mon Tom - that was only around 30 seconds over 10 miles. That works out to WAY less than than 2 minutes per 40km. ;)

Rik

jesus tom...

what the hell is sib1 et al going to see when they see the testing of the "twins"?

;)

g

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greg
www.wattagetraining.com

You mean his anecdotal report? The problem, of course, is we cannot know that everything else was the same. It is not possible to attribute all the improvement to the frame. All he showed is that in order to go faster for the same average power he must have been more aerodynamic. He does not demonstrate unequivocably that the improvement came about because he changed frames.

There are enough P3C's out there and the purported advantage is so large it should be relatively easy to compare the racing improvement (if any) of those who change to the machine compared to those who do not change or see the decrease in performance seen by those who change back to other bikes. If the claimed effect of the bike is real, it should hold for everyone and be easy to demonstrate. That evidence would be convincing to me that there is a real benefit to the frame and about how large it is, if there were a statistically significant correlation. I am sure R. Chung could tell us how it could be done.

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Frank,
An original Ironman and the Inventor of PowerCranks

"it's also possible you could be faster changing from a P3C to a P2K with the same perceived held position."

Possible? Maybe, but not likely in what we fondly call the real world.

Are you going to provide some evidence for your assertion?

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.

And so on...

-Eric

Anecdotal report!? I described exactly what was the same and what was different (hint: almost nothing) between the two setups. I provided photos. I provided a summary of an in-depth data analysis of six separate races.

I'd give you the raw data if there was a chance in a million that you had any clue as to what it is, much less what to do with it.

Your title from another thread describes your contributions to this thread perfectly: "I am really confused, clearly I don't understand something. . ." That should be your signature line from this point forward.

Rik

The shapes of our bodies are quite different, too.

Of course, it's probably not surprising that there's apparently no interaction between body shape/position and the advantage of the P3C over the P2k (P2T), since 1) much of a bike is below/in front of the rider, and 2) there's very limited evidence for significant bike/rider interaction effects regardless of bike design (the sole exception that I can think of was the Trimble).

as Tom's previous testing (many different setups that had nothing to do with this particular arrangement), has shown a repeatability of ~0.001, it's is quite reasonabe to state his results for this test as showing a delta CdA of 0.023 +/- 0.001-0.002 m2.

So, no, I do not believe 100.00000% of the measured changes were due to changing bikes. I believe at least 95% were and the other 5% due to various noise factors amongst which changes in position are included.

Yesterday I was analyzing a sizeable data set for someone. This was in a different country, different conditons, different monkey and whilst riding in unfamiliar surroundings. The repeatability of the results taking the baseline and repeating that test at the end: 0.001 m2 !!!

It's either a global conspiracy or structured field testing really can produce results that consistent. I figure #2.

As pointed out, shrugging and other changes in posture can result in significant changes in aerodynamics. Maybe it's not possible for these changes to account for all of the measured difference between frames (I don't know) but if they can account for some of the difference, then creating a rule of thumb such as "The P3C saves 2s per km" is not appropriate.

Not that there's anything wrong with global conspiracies. The pay is better and now you get a choice of health plan.

You can learn a lot by bookending the trials.

 

Ah, so the lack of blinding no longer invalidates any difference, now you're just saying any difference has to be taken with a pinch of salt. OK, I can live with that.

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What were his expectations going into the head-to-head test of P2K and P3C? Probably that the P3C was faster. These expectations could have manifested themselves as changes in position. After all, Tom's a human being and not a mechanical test rig.

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Sure, but your argument appears to be predicated on assuming that those putative subconscious changes in position reduced an already optimized CdA rather than increasing it. Or are you saying that the true difference may be even larger than the one Tom measured?

So maybe he didn't shrug on the P3C, instead maybe he sat up a bit on the P2K. Maybe he held his optimised position just a little better on the P3C. Not hard to imagine that this could happen, is it?

You seem to think Tom is immune to such bias and error. Why did Tom do the test if he didn't expect there to be a difference? I think all we are saying is blinding is good scientific protocol. Failure to blind introduces potential error. This result suggests that there is a big difference. If such a real world difference in frames alone actually exists it should be able to be extracted from the gobs of race result data available and analyzed statistically. That is where the proof of your contention lies. Don't you agree?

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Frank,
An original Ironman and the Inventor of PowerCranks