Am I missing something about the Ventum? I've seen the bike in person at least a dozen times now and can't recall any asymmetries. Also, supposedly Z frames do well at low yaw and less well at high yaw.

The chainstays are quite different on either side. I'm not aware of anything on the others that would cause that degree of asymetry.

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Disc brakes

And even then that 24-25mph is the pointy end of the field. I would reckon that back 2/3rds are averaging 20mph or less.

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I don't understand why it can't be published in both cda and grams and whatever else?
Is the internet running out of space? Publish in whatever you want with a hyperlink to whatever Tom wants.

The TEST was in 30 mph. The conversion to a range of race speeds, including yours, is valid by the rule of thumb:

10 grams of drag measured at 30 mph ~= 1 watt at common race speeds

100 grams "" ~= 10 watts ""

How can I communicate this in a way that there is not confusion?

Actually, that's the value that requires more assumptions than any other. And some of those assumptions -- like yaw weights, which Tom mentions offhand as if it's a simple thing -- are quite complex and involved and dependent on other variables that are specific to a given course and rider and day.

There's really no downside to also reporting in CdA. And I already said I would do this in some way shape or form.

And time-course figures are core to the report as well. You will know how much time these differences imply for a variety of courses and days for riders of different ability levels.

But the way the report is written there are certain inferences I cannot make and comparisons I cannot draw (to other research and studies) without putting units in grams of drag. Where possible, I can also report in CdA.

This is never going to be all things to all people. But my hope is that most people, especially those who funded it, can interpret the results from the way they are presented in a way that is meaningful to them

And even then that 24-25mph is the pointy end of the field. I would reckon that back 2/3rds are averaging 20mph or less. //

And your point? I think we can all figure out that if the test is at 30mph and we ride less, then our watt savings will also be less. They have to pick some speed to do these at, so 30 is a good round number that highlights differences a lot more effectively than 20 would. If you did all the tests at 20mph you would likely be within the margin of error most of the time and the tests would be less valid.


I would rather know that I was saving 10 watts going downhill slightly from a test than say 2 watts doing 14mph up a grade. One I could be fairly confident in my savings, the other would be a toss up...

I believe 1 is P5-6 as well ... the graph -10 to +10 looks very similar to the Cervelo White Paper.

I hope that

a) Premier Tactical is the other bike in 1 or 2 ... just because I like the looks and the way the owner communicates

b) The Felt B2 is not No 6 ... this would put an outdated mid-range frame on par with many of the latest "superbikes" - although I am not sure Kiley would use the Andean if it is basically just as aero as his old B2 (assuming the Andean is not No 1 or No 2).

My point was that it would be interesting for once to see scaled findings. Say watts saved at 25/20/15mph

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Power to overcome aero drag is proportional to V^3. Very simple calculation.

Forget this BS of "watts saved" entirely. It depends on too many unique variables.Triathletes are supposed to be a smart bunch on average, and plugging numbers into an online calculator does not require a high IQ. Plus, anybody who understands "watts" or has a PM should have some inkling of their CdA. If it's .25 for instance, and the aero test shows a .01 difference between one frame and another, then that is 4% of your total aero drag.

If you aren't using yaw weights for other metrics then you don't need them for "time savings" either. The beauty of "time savings" is that it won't change very much for a slow rider vs a fast one, compared to watts or grams which will be 8x higher for a 30mph rider vs 15mph.

But CdA is the best thing to use.

So when do we get to see results? :))

Read further. No, it's NOT only valid at 30mph. In fact, the ROT is estimated for "typical race speeds" (i.e. ~18-19mph on up to mid-to-upper 20s) based on drag force data TAKEN at 30mph. THAT is the part which is commonly left out and/or mis-understood...and you're at least the 2nd person in this thread alone to have done so. I rest my case ;-)

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It can be. I like the suggestion of publishing the drag charts with something like CdA on the left vertical margin, and measured "grams of drag" on the right...but, I think I would include a large "measured at 30mph tunnel speed" on the grams label.

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Don't use grams as your basis for the reference, use CdA.

Think of it this way: CdA is the actual value of interest being measured by the force balance in a wind tunnel. Otherwise there would be no need to monitor the tunnel speed or the air density. All of those values are necessary to put the output in context. But, once you have the CdA, it's relatively easy to apply that info to a wide range of conditions.

You might have to start out with a quick explanation of what a drag coefficient is and the concept of "drag area", but in the end it will be worth it. I think most who will be interested in this report will already have somewhat of an idea already...and for those who don't, you'll be giving them some additional insight they wouldn't get otherwise, and a tool to use in the future.

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As Ron mentioned, scaling doesn't matter much when we get down to time differences.
As an example - using IM Cairns model (with yesterdays weather conditions) and data from Felt IA release, we get the following time differences between the IA and a Shiv

Time difference in m.ss, IA faster in every case.

Adjusted weather factors how conditions change for the slower riders. Unadjusted gives everyone the same weather.
The wind conditions make the table above slightly unusual - normally the numbers for each split are more consistent.

If you want to understand power scaling per speed, I included this handy table in a post a couple of years back:


So a 10w difference for a 4.30 rider (40kph) scales down to 3 and a bit watts for a 6.30 (27kph) rider. But as you see from the first table - the time differences don't scale the same way.

Without giving anything away about Kileys results, you are going to see the same consistency of time advantage across different rider speeds.

Just a suggestion.... you may want to include some math or an example/evidence that shows this. "Race speeds" is still kinda vague IMO. I know the math would be over the head of almost everyone and putting it in the actual report will probably lose most readers. This statement has been put out there several times but I have yet to see someone show the math publicly that proves it.

I've done the math myself and it works out mostly. But for those that are OCD like me, I will say the 100 grams ~= 10 watts is just a generalization. There are those that want more than a blanket statement but I know that's not the norm.

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Put the math in it and if the reader doesn't want to follow who cares. The readers should strive to be educated and math formulas can help.

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Without reported error, your data is about as useful as an editorial. I know that not that many people understand this...I have pulled out my hair for the past 20 years trying to explain things like this to marketing people who don't understand what science actually is. If you truly want to contribute something, then you need to present the data for people to interpret; otherwise you are just presenting what you have said in the past is just a whole load of unbelievable marketing drivel. You will have become what in the past you claimed to have taken great offense at, and spurred you to take other people's money to do this testing.


The MEANINGFUL part of the data IS the data; not YOUR interpretation of the data (which includes the way that you present it).


Stephen J

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I agree. I've been watching this very intently. I understand not putting error bars on the graph to keep it clean. But will the SD (or SE) be provided at least in a table or similar? If the data is messy with massive error then whether the differences are meaningful comes into question.

You guys are complaining about something you haven't seen yet. Kiley talked about all this stuff up front. Wait and see what you get and then complain if you think you didn't get your money's worth (I assume you donated?).

Since I've seen the nearly finished paper, there is reporting of margin of error. It is not being put on the chart simply because it would be messy. There is also plenty of math and time comparisons in there. It is not going to make the most hardcore engineers, and likely many ST'ers, perfectly happy, but I don't think we ever set out to do that. The testing had limited scale that was based on funding and logistics. I personally feel like the objectives were met in the instance. And, like most studies, more questions were also brought to the fore.

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Heath Dotson
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Not complaining, just commenting. I fully agreed there is a rationale for omitting error on the graph. Zero issues there.

Come on guys, lets see the results!