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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>

until then ...

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 [Mr. Tibbs] [ In reply to ]
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Since the old KM40 (the one with the curved down tube and 650 wheels) has been out of production for several years now, and since I own one, I often wonder how it would stack up aerodynamic with the newer bikes like the P3 and Specialized Transition. It seems like if it was properly outfitted with vision tech handlebars, disk wheel, and tri spoke front wheel, it would have to be pretty close, but I'm just an uninformed enthusiast grasping straws perhaps.

Geoff from Indy
http://www.tlcendurance.com
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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>

<chirp....chirp...chirp>

http://bikeblather.blogspot.com/
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Re: Kestrel Wind tunnel data [gtingley] [ 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

Hey hey hey, slow down ---- Let's be scientific. The tare values at A2 and San Diego ARE NOT THE SAME! The tunnels are not the same. The data can not be compared like that. We took our control bike to 5 different tunnels last year and while 0 degrees generally lines up, yaw does not. We've talked about this on ST before. And I have to read lower in this thread too, but just got to this post and had to raise a red flag.

Mark

--
Mark Cote
MITAerobike
Specialized Bicycle Components
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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?

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.
MIT Aerobike Response --- Nope, I subtract tares so that the raw corrected values are representative of real world drag values that can be used when comparing to power testing. I don't have an apparatus mounted to my bike when I do power testing, so I don't include that drag. If there is assumed very little apparatus interaction with the bike, then the tare should be subtracted. At MIT, it wasn't a good idea to subtract because there was a fair amount of apparatus interaction with the bike. At A2, there isn't, so I subtract tares. We publish in grams of force because people like seeing that. I study in CdA (m^2) and want all of my wind tunnel data to be useable for real world simulations.
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--
Mark Cote
MITAerobike
Specialized Bicycle Components
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Re: Kestrel Wind tunnel data [MITaerobike] [ In reply to ]
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--- Nope, I subtract tares so that the raw corrected values are representative of real world drag values that can be used when comparing to power testing. I don't have an apparatus mounted to my bike when I do power testing, so I don't include that drag.

Yeah...I was thinking the same thing when Carl made that comment...why wouldn't you want to subtract the tare. That would make it slightly easier to compare across tunnels too, right?


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We publish in grams of force because people like seeing that.

I think it's time to start changing that paradigm and publish in CdA (m^2) as the primary "units" ...and just give "grams @ 30mph, STP, etc." as a reference :-)


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I study in CdA (m^2) and want all of my wind tunnel data to be useable for real world simulations.

Amen...but, does that mean you've convinced the A2 folks to report CdA in m^2 instead of ft^2 ;-)

http://bikeblather.blogspot.com/
Last edited by: Tom A.: Oct 14, 09 15:49
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Re: Kestrel Wind tunnel data [Tom A.] [ In reply to ]
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Still no Steven, huh? That's a shame.
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Re: Kestrel Wind tunnel data [hgrong] [ In reply to ]
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Still no Steven, huh? That's a shame.

As I wrote earlier today:

<chirp....chirp...chirp...>

http://bikeblather.blogspot.com/
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Re: Kestrel Wind tunnel data [Tom A.] [ In reply to ]
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All,

Sorry for the chirp chirp as you like to say...

So, let me explain how Kestrel does our testing and why I feel that a complete bike test benefits the consumer.

First, all my design and testing is done @ the A2 Tunnel. I feel that it is the one of greatest assests I have that there is a tunnel with expertise available.

Testing was done on all bikes with Zipp Disc ad Zipp 404 and also tested with Zipp 404 and 808's.

The goal was to see how each wheel affected the bike. We also tested multiple bars on each bike along with specific components. Again, how do parts change the data on the complete bike.

I tested the same size bikes, same saddle height, same bar height.

Bars tested were what I spec on bikes. 3T Mistral Pro, Zipp Vuka, and Profile Cobra Wing with T-1 Viper Extensions. Each bike was tested with the same bars since I know that this would affect the test.

I left the drive train components alone meaning that if Brand X used Shimano Dura Ace and I spec'd Sram Red, it would remain the same.

I also used 23mm tires on all bikes.

The one issue is that you can NOT compare data from one tunnel test to another @ the same tunnel or from tunnel to tunnel. So what you see from a competitor's test will show differently.

Hope that answers some questions.
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Re: Kestrel Wind tunnel data [sharad] [ In reply to ]
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All,

Sorry for the chirp chirp as you like to say...

No problem...you're a busy guy after all ;-)


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So, let me explain how Kestrel does our testing and why I feel that a complete bike test benefits the consumer.

First, all my design and testing is done @ the A2 Tunnel. I feel that it is the one of greatest assests I have that there is a tunnel with expertise available.


Mark Cote speaks highly of them as well...


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Testing was done on all bikes with Zipp Disc ad Zipp 404 and also tested with Zipp 404 and 808's.


So...what wheels were on the particular bikes in the plot shown in the first post in this threas?



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The goal was to see how each wheel affected the bike. We also tested multiple bars on each bike along with specific components. Again, how do parts change the data on the complete bike.

I tested the same size bikes, same saddle height, same bar height.


Do you mind if I ask how the saddle heights and bar heights were measured?




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Bars tested were what I spec on bikes. 3T Mistral Pro, Zipp Vuka, and Profile Cobra Wing with T-1 Viper Extensions. Each bike was tested with the same bars since I know that this would affect the test.

Does that mean that each bike in the test (including the competitors) was tested with each bar? If so, again, what configuration does the plot represent?



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I left the drive train components alone meaning that if Brand X used Shimano Dura Ace and I spec'd Sram Red, it would remain the same.

I also used 23mm tires on all bikes.


Fair enough.



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The one issue is that you can NOT compare data from one tunnel test to another @ the same tunnel or from tunnel to tunnel. So what you see from a competitor's test will show differently.


Are you saying that the repeatability of the A2 tunnel in respect to CdA measurements isn't very good? Or...are you commenting on the drag values in grams?



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Hope that answers some questions.

It's a start ;-)

http://bikeblather.blogspot.com/
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Re: Kestrel Wind tunnel data [sharad] [ In reply to ]
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Steve-
Could you just list the parts that were used on the 4 bikes to get the 4 lines on your graph?

i.e.
P3C-
bars -brand x
front wheel - brand z model a
rear wheel - brand z model b
....
4000-
bars -brand h
front wheel - brand z model c
rear wheel - brand z model d
....
also the big tunnel next door has very little problem repeating test session to test session, why would the small tunnel be any different?
bars
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Re: Kestrel Wind tunnel data [MITaerobike] [ In reply to ]
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We took our control bike to 5 different tunnels last year and while 0 degrees generally lines up, yaw does not. We've talked about this on ST before.

Hmmm. I missed that thread, and it is pertinent to something I'd wondered about for a while. Can you point to that discussion?
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Re: Kestrel Wind tunnel data [RChung] [ In reply to ]
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I have to say i do appreciate the fact that some engineer like Mark Cote and Gerard take part in our discussion because the level of precision and explanation they give to explain there testing is just on a differente level. Make things a lot more clear and transperante to me.

Jonathan Caron / Professional Coach / ironman champions / age group world champions
Jonnyo Coaching
Instargram
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Re: Kestrel Wind tunnel data [sharad] [ In reply to ]
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As others have said; thanks for replying! Just the two questions from me:

What speed was the test run at?

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The one issue is that you can NOT compare data from one tunnel test to another @ the same tunnel or from tunnel to tunnel. So what you see from a competitor's test will show differently.

I can understand that the values might not be the same, but surely the shape of the curves should be largely similar if not the same?

Regarding your point about results which shouldn't be directly compared; people might be interested to know that it's been revealed recently that is how the aero data on the HED site was obtained (apparently using different protocol too).
Last edited by: zebragonzo: Oct 15, 09 9:40
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Re: Kestrel Wind tunnel data [RChung] [ In reply to ]
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We took our control bike to 5 different tunnels last year and while 0 degrees generally lines up, yaw does not. We've talked about this on ST before.

Hmmm. I missed that thread, and it is pertinent to something I'd wondered about for a while. Can you point to that discussion?

Hmmm...I found these 2 posts merely by searching on "control" and author "MITAerobike" ;-)

http://forum.slowtwitch.com/...ing=control;#2014644

http://forum.slowtwitch.com/...ing=control;#2394452

http://bikeblather.blogspot.com/
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Re: Kestrel Wind tunnel data [Tom A.] [ In reply to ]
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There are three big research projects we did in aero in parallel with Transition/Shiv development over the past two years:

1. Comparison on a control bike at several different wind tunnels (A2WT, UWAL, SD LSWT, MIT WBWT, AAT Fort Collins)

2. Long term testing repeatability of a control bike at the A2 Wind Tunnel

3. Comparison of Road versus Aero gear for TT/Tri racing (wind tunnel and power testing study)

The first two were internal studies, the third I've posted up here before. I'll continue to share parts of the internal studies as appropriate.

Cheers,

Mark

--
Mark Cote
MITAerobike
Specialized Bicycle Components
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Re: Kestrel Wind tunnel data [MITaerobike] [ In reply to ]
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There are three big research projects we did in aero in parallel with Transition/Shiv development over the past two years:

1. Comparison on a control bike at several different wind tunnels (A2WT, UWAL, SD LSWT, MIT WBWT, AAT Fort Collins)

2. Long term testing repeatability of a control bike at the A2 Wind Tunnel

3. Comparison of Road versus Aero gear for TT/Tri racing (wind tunnel and power testing study)

The first two were internal studies, the third I've posted up here before. I'll continue to share parts of the internal studies as appropriate.

Cheers,

Mark

Damn...you've got a fun job...I'm jealous :-)

http://bikeblather.blogspot.com/
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Re: Kestrel Wind tunnel data [Tom A.] [ In reply to ]
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"Damn...you've got a fun job...I'm jealous :-)"

x2. Beats the hell out of designing and testing the watertightness and/or EMI radiation characteristics of, say, a modified Gichner S280 military shelter.
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Re: Kestrel Wind tunnel data [Tom A.] [ In reply to ]
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Zipp Disc and 404 were used on the chart shown.

Saddle height I'll have to check although each bike was the same as were the bars.

Each bike was tested with each bar. The test shows the Zipp Vuka bar.

What I am saying is that every time you go into a tunnel it is an individual test. You can't compare one tunnel test to another test. Has nothing to do with the tunnel quality.
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Re: Kestrel Wind tunnel data [sharad] [ In reply to ]
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Speed?
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Re: Kestrel Wind tunnel data [sharad] [ In reply to ]
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so this thread keeps saying wind tunnel data....will there be a release of the actual paper at some point in the near future?

also, do you have geometries on the 4000?

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
Garmin Glycogen Use App | Garmin Fat Use App
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Re: Kestrel Wind tunnel data [sharad] [ In reply to ]
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Something is just not right about this.

The BIG issue was if they used the same wheels and bars on all bikes for these tests. Kestrel is now saying they did. Why not release that information when the results were made public? Why wait two weeks during which time lots of negative stuff is written about your company? That and the fact that your competitors bikes are shown to produce over 100 grams more drag at 0 degrees then multiple independent tests.

Something just does not add up.
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Re: Kestrel Wind tunnel data [sharad] [ In reply to ]
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Zipp Disc and 404 were used on the chart shown.

Saddle height I'll have to check although each bike was the same as were the bars.

Each bike was tested with each bar. The test shows the Zipp Vuka bar.
Then the chart is wrong in saying that "each bike was tested as supplied to the consumer"?
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Re: Kestrel Wind tunnel data [Andrew Coggan] [ In reply to ]
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It appears that no amount of time responding to questions will be sufficient to those in this thread, so I am surprised Kestrel even spends any time addressing it.

---
Team Triabetes
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Re: Kestrel Wind tunnel data [sharad] [ In reply to ]
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It looks like Kestrel designed the most aero bike that they could, fair enough.
However, that transition between the seat post and the seat stays reminds me of a full-suspension mountain bike. I think a lot of energy will be wasted per pedal stroke by having that notch.

Am I on crack ? Is there a way to test power transfer between bikes - i.e. is this frame stiffer or as stiff as the others ?

I'm just wondering, I really NEED a new TT bike for next year :) .
Thanks - Mark
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