There will always be questions. But, the issue comes when something is published that basically says "look how great our new bike is...it's the fastest on the planet" and there is really nothing too concrete about how the testing was done, etc. Or, the small print says one thing like "bikes were tested as they would be delivered to the consumer" when maybe only one of the bikes would be delivered to the consumer with race wheels. You can punch holes in any study that gets published, and if you publish something that is less than complete or at least less than open with how things have been done, you can expect to have lots of questions...especially by folks who have done similar windtunnel or PM/outdoor testing like AC, MITaerobike, TomA, and others.

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Brandon Marsh - Website | @BrandonMarshTX | RokaSports | 1stEndurance | ATC Bikeshop |

So we should just accept the numbers even though by Kestrels own admission the chart is wrong?

IF they want to sell bikes in a packed field with a for crap economy...... I'd say it's in their BEST interest !

The chart is not wrong and maybe I'm not explaining it well.

We tested in a fair way that we believe shows real #'s.

To you the consumers, we tested with the same wheels, bars, etc. We ALSO tested as the bikes come to you the consumer which is really all how I feel the industry should test complete bikes that the consumer rides. I choose parts based on what I know works both mechanically and in the tunnel. Note that my bar selection on the bikes at the high end is my most aero bar tested. Same with wheels.

Wind tunnel data can be picked apart and I'm happy to have the new Kestrel 4000 tested by independently.

So which data are presented in the chart?

I'm sorry...I probably wasn't clear. I meant to what reference were each measured? The ground?



I'm not so sure if the folks at A2 would totally agree with such an absolute statement. There HAS to be some measure of repeatability possible...otherwise, what's the point? Yeah, the tests won't be exactly the same, but they should be able to repeat the results to within +/- some value of CdA.

Is it possible you guys could post pics from the runs? Those always help explain things a LOT...

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http://bikeblather.blogspot.com/

He answered that before. The chart in this thread is with Disc rear, and 404 front with Vuka aerobars.

Chris

Steve said "the chart is not wrong", which could be interpreted to mean that he stands by the data presented, OR to mean that they are from bikes as delivered to the consumer.

If you are saying that the chart shows drag numbers for bikes as they are delivered to consumers I may believe you.

If you are saying that the chart shows drag numbers with ALL bikes equipped with aero wheels then I say bullshit.

I think you said option 2 was the setup for the chart so I am saying I don't believe you.

Your company may have made an amazing bike but in my mind you have totally blown your credibility with the way you have presented the data. Why not come clean and just answer the questions put to you?

nobody cares what you believe. They posted date, and then explained what it is and how they got it. Go back to riding your P3.

chris

If I had wanted your input I would have asked for it. Fuck off!!!

I don't remember anyone in this thread asking for your opinion either, but that didn't stop you from spouting off.

The difference is my questions and comments were directed to the OP. That's how this forum thing works. You or your buddy Christopher may not like my questions. No problem. I don't like marketing bullshit or people not answering direct questions on a topic they started.

Could I just point out several things that make the data look slightly amateur:
1) Data analysis - I can see data, but where's the analysis (or is that a prelude to this thread?)
2) Scientists use straight lines, marketing people use curved lines; unless you know how the data varies between two points, assume it's linear.
3) Basic information is missing; the speed was the test conducted at is one such key bit of info.

Amateur??

I would have to say that you should take that up with the A2 guys since this is what we receive from them.

Great debates none the less but I will tell you I stand by the data.

The A2 tunnel is one of the best and the data and chart were supplied and reviewed while I was @ the tunnel. Nothing has been changed from their report.

I tried asking politely ;-)

Just because it comes from the wind tunnel, it doesn't automatically make them right.

Also, what speed was the testing done at?

If 'scientists' use straight lines for stuff like this, I'd suggest they're implying a level of linearity which simply isn't there. If there was anything to be learned from the Hed data taken at 2.5 degree sweeps, it's that the data isn't necessarily linear.

Granted we're talking about wheels vs. bikes, but I still wouldn't assume the data is linear between 5 degree points. I actually think the way it's presented here is more reasonable, regardless of 'what scientists may think'.

I would actually think that 'scientists' wouldn't connect the dots in the first place....

You may be missing the point - you don't assume that the data is linear, you use linear data unless you can prove otherwise.

edit - remember that there is only one straight line that can be drawn between points, there are an infinite number of curves.

I get the point, but as a non-scientist I actually think that the curved line presents an ambiguous interpretation which is probably more representative of reality--at least to this layman.

yes but that doesn't mean the data doesn't show this. Just because they marked the major points 5,10,15 etc doesn't mean they didn't collect data through the whole range.

You can't mark a data point every .000000001 degrees thats what a line is for. You're assuming they only collected 5 points of data during the sweep which i doubt is true.

Scientists would connect the dots, with straight lines, because it makes the data much easier to see than scatter plot, especially when it's small. It's hard to see which points are related.

The one other thing that scientists would do is include error bars at each data point, but that's probably asking too much.

The reason that you do not connect with a curved line is that is makes an implication of what is not there. I'm sure A2 does it because they are in the marketing business as well. There are now enough windtunnels that there is competition for bike testing business. The curved lines look "pretty," but they are incorrect.

If you connect the dots with straight lines, everyone knows it simply for visual clarity. If you connect it with a curved line, there can be the assumption that there actually is a fit that has been applied. Unfortunately, in this case, there was not. You don't know if the data goes from a-to-b like this / or like this _| or like _( or like ^ or... (sorry, I ran out of approximations using common characters). The data could move logarithmically or exponentially or parabolically, all which would mean very different things. And when you put an arbitrary curve in, that is, as zebragonzo said, "amateur."

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"Non est ad astra mollis e terris via." - Seneca | rappstar.com | FB - Rappstar Racing | IG - @jordanrapp

No, it is true. That's how you measure. In ~2.5deg increments. Every time you rotate the balance, you have to then wait for the reading to stabilize. You don't take measurements while the balance is in motion.

They do collect more than five (or ten) points, but it's multiple sets of data at those same five (or ten) points and you also hit those points twice per run (if you are testing correctly) - on the sweep out and then the sweep back in. I.e., you have Run_One[0, 2.5, 5, 7.5, 10, 12.5, 15, 17.5, 20, 17.5, ... , 0], Run_Two[..], Run_Three, etc. Then you take an average value at each point, which is also what yields the error margin for each reading. You probably also kick out a bad run, if you have one set where the data is way outside the normal deviation.

They definitely don't measure every 0.00001 degrees.

The criticisms that everyone has made of the way the data has been presented are valid.

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"Non est ad astra mollis e terris via." - Seneca | rappstar.com | FB - Rappstar Racing | IG - @jordanrapp

Okay good to know.. makes sense.

I was more concerned with that we have no clue what bike was actually tested more then the curved data lines. I can deal with that.

IMO a more likely explanation is simply that whomever drew the plot just wasn't anal-retentive enough to change the default setting in Excel...

Hmmm. You are missing the point zebragonzo made.

He didn't question the data behind what was presented. I don't think anyone really questions the data coming out of A2.
He (and others) questioned what was presented.
Who made the chart, Kestrel or A2?
The title says "ANALYSIS". Where is the analysis?
Where is the rest of the data that A2 no doubt provided?
What speed/condition/dynamic pressure was used or normalized to?
Others have asked specifically about frame of reference for heights and angles, wheels tested vs wheels delivered etc etc. Where are the answers?

Hmmm.