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Re: Kestrel Wind tunnel data [chicanery] [ In reply to ]
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He's here in kona. It is entirely possible that he's been simply too slammed while out here and hasn't yet had the time to respond.

Heading that way now. If I see him I'll ask

36 kona qualifiers 2006-'23 - 3 Kona Podiums - 4 OA IM AG wins - 5 IM AG wins - 18 70.3 AG wins
I ka nana no a 'ike -- by observing, one learns | Kulia i ka nu'u -- strive for excellence
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Re: Kestrel Wind tunnel data [Carl] [ In reply to ]
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We don't subtract out tare drag...to arrive at our comparison #s

Why not? That is, what is the logic behind this decision?
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Re: Kestrel Wind tunnel data [chicanery] [ In reply to ]
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dont be silly

he just posted in another thread a few minutes ago about the kestrel pro msrp or something like that. He as plenty of time to post as it s part of the job to be on slowtwitch if you are smart marketing wise.

He seems like a smart guy and milking this thread to the max and letting it go up in view and post before chipping in.... smart marketing. He will chip in when the thread start to die...


,

Jonathan Caron / Professional Coach / ironman champions / age group world champions
Jonnyo Coaching
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Re: Kestrel Wind tunnel data [MarkyV] [ In reply to ]
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He's here in kona. It is entirely possible that he's been simply too slammed while out here and hasn't yet had the time to respond.

Heading that way now. If I see him I'll ask

That's what Steve said in another thread -

Re: Kestral airfoil pro SE [sharad]
In Reply To:
Wind tunnel thread is interesting. I'm a bit slammed in Kona right now so give me until next week and I will chime in. Suffice it to say, the results are legit and tested in multiple ways against many of the bikes.

Off to the last day of the Ironman Expo.

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Re: Kestrel Wind tunnel data [Tom A.] [ In reply to ]
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"I mean if the P4 is faster then the 4000 by a few seconds but I really dig the 4000 doesn't that count? "

I said if and the point of the post was to take into account someone's love for thier bike. I didn't say the 4000 and P4 where equals.

customerjon @gmail.com is where information happens.
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Re: Kestrel Wind tunnel data [Carl] [ In reply to ]
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Dangit, now I'm a hijacker too...


With 150-180g of tare drag "left off" I don't see any reason to doubt the Shiv #'s are real ... Let's play the game and say it's not...and .. 150-180g more drag via setups


OK, so if I'm tracking with you correctly, this P3C below I tested at 689g at 0deg yaw in 2006 at LSWT

Below that is the Cervelo test, backs my numbers up, as does the test by Andy at TAMU (on a P3T)

so, subtract 150 to 180g for the tare ... you get to 500-530g

right in step with the Shiv's numbers from A2

so...

TTX 680g
P3C 680g
Shiv 650g (corrected for +150g tare)
P4 575g




Last edited by: gtingley: Oct 9, 09 14:25
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Re: Kestrel Wind tunnel data [Andrew Coggan] [ In reply to ]
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In Reply To:
We don't subtract out tare drag...to arrive at our comparison #s

Why not? That is, what is the logic behind this decision?

Why? It's a constant unless you believe there's interaction between the bike and the struts that varies by bike as well as by yaw...or does this belong in a different basket than the rider-bike interaction you keep pointing out doesn't exist except in extreme cases?


So my question stands: does everyone else seem massively off the back once you put the tare drag back in?


Carl

Carl Matson
Last edited by: Carl: Oct 9, 09 14:40
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Re: Kestrel Wind tunnel data [gtingley] [ In reply to ]
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How much time over a 40k does -105g gain you? For real, I swear I am not being an ass.

customerjon @gmail.com is where information happens.
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Re: Kestrel Wind tunnel data [gtingley] [ In reply to ]
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Yes, that's exactly the road I'm trying to take you down. Though I might quibble with your inclusion of the P4...since it doesn't appear on the Cervelo chart you showed.


Carl

Carl Matson
Last edited by: Carl: Oct 9, 09 14:38
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Re: Kestrel Wind tunnel data [Carl] [ In reply to ]
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In Reply To:
In Reply To:
In Reply To:
We don't subtract out tare drag...to arrive at our comparison #s

Why not? That is, what is the logic behind this decision?

Why? It's a constant unless you believe there's interaction between the bike and the struts that varies by bike as well as by yaw

No, that wasn't what I was attempting to imply...I just wondered why you wouldn't correct the data since you obviously have gone to the trouble of measuring the "wind on" tare.

In Reply To:
So my question stands: does everyone else seem massively off the back once you put the tare drag back in?

Obviously not, but here is why I am confused: I've always understood that they do correct for the tare at TAMU*, and since my wife's bike and Gary's bike appeared to have similar drags, assumed that the same was true at the LSWT. That is why I am/was so impressed by the numbers that Mark keeps quoting for the Shiv.

*I know for a fact that they do when presenting bike+rider data.
Last edited by: Andrew Coggan: Oct 9, 09 15:01
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Re: Kestrel Wind tunnel data [Carl] [ In reply to ]
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Yes, that's exactly the road I'm trying to take you down. Though I might quibble with your inclusion of the P4...since it doesn't appear on the Cervelo chart you showed.


Carl

got it ... I added the links to each test on the title of the model, if you roll over the model titles in my post above, you can click the links

here is the P4 test http://www.mpstraining.com/firm-news/drag2.jpg
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Re: Kestrel Wind tunnel data [Mr. Tibbs] [ In reply to ]
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How much time over a 40k does -105g gain you? For real, I swear I am not being an ass.

The aero rule of thumb is 50g = 0.5sec/km at 30mph
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Re: Kestrel Wind tunnel data [Andrew Coggan] [ In reply to ]
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In Reply To:
In Reply To:
In Reply To:
In Reply To:
We don't subtract out tare drag...to arrive at our comparison #s

Why not? That is, what is the logic behind this decision?

Why? It's a constant unless you believe there's interaction between the bike and the struts that varies by bike as well as by yaw

No, that wasn't what I was attempting to imply...I just wondered why you wouldn't correct the data since you obviously have gone to the trouble of measuring the "wind on" tare. Nothing to correct. Nothing measured either, for that matter. The only reason to measure it is to do something like Specialized did and wow everyone with #s that, upon thoughtful examination, maybe aren't all that special. At least they were up front about what they did, and now Mark has cued us in on the magnitude of what they did, and for that we should all be grateful.

In Reply To:
So my question stands: does everyone else seem massively off the back once you put the tare drag back in?

Obviously not, but here is why I am confused: I've always understood that they do correct for the tare at TAMU, and since my wife's bike and Gary's bike appeared to have similar drags, assumed that the same was true at the LSWT. That is why I am/was so impressed by the numbers that Mark keeps quoting for the Shiv.

details details... ;-)


Carl

Carl Matson
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Re: Kestrel Wind tunnel data [jmhtx] [ In reply to ]
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Ignore the number differences for the moment and look at the shapes.

Cervelo says that the P3 is best at 10° and going an extra 5° adds about 50g onto the drag. According to Kestrel, the P3 bottoms out at 15°, which is about 50g better than at 10°.

PS. I work on the principal of not trusting people who use curves instead of straight lines to join the dots!
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Re: Kestrel Wind tunnel data [gtingley] [ In reply to ]
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Thanks...but I'm still not quite on board with the P4 data. The charts you link to for the P3C and the P4 seem to be based on the same datasets, the legend on the latter chart showing the same LSWT run codes (#s in front of the bike names) as on the former but the data have been rotated about 0deg yaw by a factor that is congruent with a cos beta squared correction. Could be something else I suppose. Anyway, not necessarily a big deal by itself, but that same familiarity with LSWT's date code convention (the 4digit code in the title of the chart containing the TTX, and the 4digit code after the P4 in the other chart's legend) also tells me the P4 data was likely generated some 7-8mo after everything else on the chart and dropped in there without any indication to that effect other than 4 extra numbers in the legend that few people will recognize or understand the potential significance of.


Maybe Cervelo has done something similar to Specialized's 6mo control study (cool stuff BTW), wouldn't surprise me, but I've seen no mention of it. Maybe there's another explanation altogether. In the meantime I, for one, don't take the chart with the P4 at face value.


Carl

Carl Matson
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Re: Kestrel Wind tunnel data [gtingley] [ In reply to ]
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But isn't the elephant in the room the Kestrel 4000 at around 500 g-f tared out?

I have to say though as time passes, I'm less and less interested in Kestrel's explanation of that chart (curvy or not).

To Carl: heck where's that Speed Concept data and the 2010 rollout? ;-)
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Re: Kestrel Wind tunnel data [rmur] [ In reply to ]
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But isn't the elephant in the room the Kestrel 4000 at around 500 g-f tared out?

Who says that the struts aren't tared out already? See...that's the problem...insufficient details.

http://bikeblather.blogspot.com/
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Re: Kestrel Wind tunnel data [Tom A.] [ In reply to ]
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But isn't the elephant in the room the Kestrel 4000 at around 500 g-f tared out?

Who says that the struts aren't tared out already? See...that's the problem...insufficient details.

DA 725g http://i33.tinypic.com/25jjszm.jpg
TTX 680g http://i33.tinypic.com/25jjszm.jpg
P3C 680g http://i33.tinypic.com/25jjszm.jpg
4000 675g (corrected for +150g tare) http://www.xtri.com/...p/img_rep_5981_1.jpg
Shiv 650g (corrected for +150g tare) http://forum.slowtwitch.com/...post=2536314#2536314
P4 575g http://www.mpstraining.com/firm-news/drag2.jpg
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Re: Kestrel Wind tunnel data [gtingley] [ In reply to ]
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In Reply To:
In Reply To:
In Reply To:
But isn't the elephant in the room the Kestrel 4000 at around 500 g-f tared out?

Who says that the struts aren't tared out already? See...that's the problem...insufficient details.

DA 725g http://i33.tinypic.com/25jjszm.jpg
TTX 680g http://i33.tinypic.com/25jjszm.jpg
P3C 680g http://i33.tinypic.com/25jjszm.jpg
4000 675g (corrected for +150g tare) http://www.xtri.com/...p/img_rep_5981_1.jpg
Shiv 650g (corrected for +150g tare) http://forum.slowtwitch.com/...post=2536314#2536314
P4 575g http://www.mpstraining.com/firm-news/drag2.jpg

How do you account for the following data then in the grand scheme of things (i.e. where the p3C and Transition are fairly close, yet the Shiv is much better than the Transition?)





http://bikeblather.blogspot.com/
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Re: Kestrel Wind tunnel data [Tom A.] [ In reply to ]
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Those two graphs show the tare difference quite nicely I must add. And I don't know if this accounts for the difference, but didn't specialize test w/ the old wolf cl (or was it a tt) fork and not the 3t funda fork that Gerard claims is a significant improvement. I for one would be interested in knowing how much an improvement the new "cervelo" fork is over the 3t on the P3. (Further thread jacking this thread)

p.s. any engineer that uses curvy lines to connect data points should turn their sheepskin back in. That is strictly a marketing dept. thing and should remain so.
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Re: Kestrel Wind tunnel data [Tom A.] [ In reply to ]
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In Reply To:
In Reply To:
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But isn't the elephant in the room the Kestrel 4000 at around 500 g-f tared out?

Who says that the struts aren't tared out already? See...that's the problem...insufficient details.

DA 725g http://i33.tinypic.com/25jjszm.jpg
TTX 680g http://i33.tinypic.com/25jjszm.jpg
P3C 680g http://i33.tinypic.com/25jjszm.jpg
4000 675g (corrected for +150g tare) http://www.xtri.com/...p/img_rep_5981_1.jpg
Shiv 650g (corrected for +150g tare) http://forum.slowtwitch.com/...post=2536314#2536314
P4 575g http://www.mpstraining.com/firm-news/drag2.jpg

How do you account for the following data then in the grand scheme of things (i.e. where the p3C and Transition are fairly close, yet the Shiv is much better than the Transition?)



I don't think the L is really a truly comparable bike to a 56. There's a lot less bike on a L than a 56. I brought that up with Mark in a previous thread. Not sure how that factors in, but it's something to consider. I think the XL and 56 are much more comparable. I.e., that's the size I'd ride in each. The L would be much too small (need like a 13cm stem on the L vs. a 10cm stem on the 56 P3C to achieve the same position).

"Non est ad astra mollis e terris via." - Seneca | rappstar.com | FB - Rappstar Racing | IG - @jordanrapp
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Re: Kestrel Wind tunnel data [Rappstar] [ In reply to ]
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I don't think the L is really a truly comparable bike to a 56. There's a lot less bike on a L than a 56. I brought that up with Mark in a previous thread. Not sure how that factors in, but it's something to consider. I think the XL and 56 are much more comparable. I.e., that's the size I'd ride in each. The L would be much too small (need like a 13cm stem on the L vs. a 10cm stem on the 56 P3C to achieve the same position).

Reach-wise, yes, but not stack-wise. The L Transition actually has ~1cm greater stack than the 56 P3C (which accounts for ~0.3cm of the shorter reach.)

Besides, the XL was changed for 2010 and now has a 2cm higher stack, as opposed to the previous years where the stacks on the L and XL sizes only differed by 1mm.

I also find it sort of interesting that you'd ride those 2 sizes...since, IIRC, I'm at least 3" shorter than you, and a 56 P3C is what I had borrowed for the "Something Borrowed..." testing (and fit great) and I'm thinking about getting a L Transition. Of course, the fact that I'm now running a Scott 100K bar probably has some influence on that (i.e. it requires a shorter stem for a given pad position than the Vision bars I had used on the P3C).

In any case, you lost the point I was trying to make, which wasn't how the P3C compared to the Transition, but how the P3C compared (by inference) to the Shiv...and how that didn't match Gary's summary above.

http://bikeblather.blogspot.com/
Last edited by: Tom A.: Oct 9, 09 21:24
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Re: Kestrel Wind tunnel data [Tom A.] [ In reply to ]
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But isn't the elephant in the room the Kestrel 4000 at around 500 g-f tared out?

Who says that the struts aren't tared out already? See...that's the problem...insufficient details.


I was looking at the P3C to 4000 differential on the Kestrel chart ~175 g-f. If the P3C 'true' baseline is ~675 g-f that puts the K4000 down around 500 g-f. If the P3C/Fuji data isn't tared out, surely they wouldn't tare out the 4000?? (!!!!)

Re the Shiv/Transition differential - just ran some averages and across (-5,0,+5) it's -82g-f for the Shiv; across (-15,-10,+10,+15) it's -190g-f. Makes Zirbel's ride at the Worlds look all the more impressive eh?

Has anyone seen any Giant Trinity Advanced (nosecone) data BTW???
Last edited by: rmur: Oct 10, 09 5:34
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Re: Kestrel Wind tunnel data [Tom A.] [ In reply to ]
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I actually think you missed the point *I* was trying to make. It seems that it is somewhat arbitrary what size bike is chosen for these tests. Or rather it seems only stack height is considered, which is maybe not the best way. Maybe it is. But that would sem to ignore the length of the bike, which has to make SOME difference.

"Non est ad astra mollis e terris via." - Seneca | rappstar.com | FB - Rappstar Racing | IG - @jordanrapp
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Re: Kestrel Wind tunnel data [Andrew Coggan] [ In reply to ]
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It would indeed be a mistake for Steven not to show up and lay out the protocol now that the data has been "released", with specifics on equipment used for all 4 frames.

<sound of crickets chirping>
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