Hey gang, I'm running between tests and meetings this morning but rest assured answers are coming. All great questions.

Hey all,

Thank you for the comments - we're working to be as thorough as possible with our data. We'll work through these questions as quickly as possible.

To answer the Y-Axis unit scale question - the divisions on the graph are 0.001m^2. The range for each graph was 0.020m^2. Ultimately, we decided to not include specific absolute values as testing set up (facility, fixturing, build, even the actual tire used) can cause differences in the absolute values between tests. All of the data collected in these graphs was collected in one test session, (though deltas were confirmed on multiple test sessions), same exact tire for all tests, and inflated to the same pressure. We will answer the specific rotational drag questions shortly, but the rotation drag was always an addition to the translational drag. The graph's range just shifted slightly higher.

Chris can discuss further on the tire choice and development of rim shapes, but the Turbo Cotton tire was selected for drag testing to show the fastest overall package (translational, rotational, Crr).

Cam

why didn't you include aero results for the enve 4.5? weight comparison given where you come out very well but then no aero - did you lose?

roval wheels have always done well on weight, often at the expense of other qualities...

Thanks Cam. I realized after I made that post that I could just scale the units off of the plot you did last year with all of the S-Works Turbos and Turbo Cottons on the CLX64 wheel, which included the TC 24...which is posted right on my blog :-)

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http://bikeblather.blogspot.com/

I am particularly interested in how you set up the Win Tunnel to measure rotational drag. Some other questions:
1. What is the difference between a radial 20 for a rim brake and a 2-cross 24 for disc wheels?
2. Flat vs round spokes. The testing of the Rail wheel was 1 watt of translational drag, but there was no rotational measurement.
3. How about some different tests of wheel-fork interaction? Can you answer the wide vs. narrow fork question?
4. Tri-spoke vs. 20 spoke vs. disc. Rotational drag difference?

P. S. If you need a set of Specialized Tri-spokes to test the last 2, I have a set you can borrow :-). I would love to know if my Tri-spoke front, with a 20mm SS, still rules on my Nose-cone Shiv at low yaw angles.

I make so many writing mistakes that it is unreal, but how do they mess up "Aeolus" repeatedly in this.

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Ok, to answer some of the questions in this thread:

- Turbo 24 vs. Turbo Cotton 24: Simple explanation - when we started doing the shape design of the current family of CLX wheels (32,50,64) the Turbo Cotton didn't quite exist yet. All our historical CFD and benchmark data was based off the Turbo 24. As you can imagine, it takes a while to fully quantify and correlate a non-exact shape like an inflated tire casing. However, the comparison testing was done much more recently (e.g. includes the recently launched Zipp 454) and in our testing, and as Tom A. pointed out, the fastest combination of translational drag, rotational drag, and Crr was with the Turbo Cotton tire. This was true for the Zipps as well. As a result, we felt it would make the most sense to publish comparison data using the fastest available total combination.

- Rotational drag ("power-to-spin"): As many of you know, it is extraordinarily hard to be able to reliably/consistently measure this with adequate resolution. Then there are complications like accounting for, or isolating tire Crr or bearing drag. In fact, Tom A. probably remembers us telling him we were working on various different methods (most of which we ditched) to do this in the Win Tunnel when he visited over a year ago. Our engineers recently developed and validated a protocol and equipment to be able to isolate out the rotational aerodynamic component at a resolution of ~50 mW. Since we devoted a lot of time and resource into developing the equipment and protocol to achieve this, I think you'd understand if we'd like to keep the specifics proprietary. Hint: involves a very careful and modified application of the Chung method in the tunnel while understanding what error terms can be neglected vs. not.

Anyways, a lot of geeking out. The CLX50s are FAST and ride very responsively.

Chris

Sounds like you found another "nail" for RChung's "hammer"...cool :-)
(Now I'm going to be racking my brain trying to figure out how you do it...does tire Crr come into play at all?)

So, on the plots that show the combined translational drag, they show the units as m^2 of CdA as well...does that mean the "power to rotate" varies in proportion to V^3, like the translational drag? Do you think the differences between the CLX50 and 64 are just the different spoke lengths? Or, is something else at play?

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http://bikeblather.blogspot.com/

Thanks for coming by and talking about these in some detail.

Hubs are a major drag component, and are hardly ever optimized for aero in the way that rims or frames are. Could you tell us more about what you've done with the 'Aero Flange' hubs?

And what explains the large low-yaw rotational drag advantage of these over the 808 NSWs?

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'It never gets easier, you just get crazier.'

Thanks for the reply. It is always cool to get insight from the engineers that really know the how and why of what make a bike fast.

Your Chung clue is intriguing, but VE doesn't make much sense to me when there is no elevation change.

I always wondered why windtunnel a don't measure current draw for the motor that turns the wheel at the wind speed of the tunnel. Don't watts = amperagexvoltage and you "know" tire Crr from roller tests. You could then measure bearing drag on a seperate fixture and sutract from the wattage consumed by the motor. This is a kinda piecemeal way to calculate rotational drag, but is there something I am totally overlooking?

I'm going to have one of our super engineers (Ingmar Jungnickel) who helped develop this method jump in to explain a bit about how CdA plays out in this situation. As for your question re: differences: spoke length certainly plays a big part. But were also able to measure differences in how different rim shapes, hub flanges, and tires rotate through the air.

You answered your own question ;-)

In theory, that's sound. In practice there is a huge error stack on a (relatively) tiny signal.

Well, they're very nice bearings. You've put together a tidy system which justifies the investment.

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'It never gets easier, you just get crazier.'

Even small changes in that can have relatively large lateral stiffness effects. Damon Rinard found that out a long time ago when he looked at the lateral stiffness of a radially laced wheel, where the only change was a "spoke heads out" vs "spoke heads in" configuration in the lacing

I could be mistaken, but I recall Jobst writing about that well before Damon came on the scene. (RIP Jobst)

Your Chung clue is intriguing, but VE doesn't make much sense to me when there is no elevation change.

The "V" is for "Virtual". Doesn't mean that you need real elevation change. The genius of the Chung method is that it represents energy changes in terms of elevation changes for the bike and rider, which are more easily conceptualized. More generally, the Chung method is an example of kinematic modeling, which is what I think Chris is hinting at.

The physics was worked out long ago. Once, there was an internet far, far away, where a physicist named Schreuder documented all this, and worked it out for the special case of the bicycle. Unfortunately it is mostly gone now, although tantalizing hints remain: http://forum.slowtwitch.com/...ost=2759184#p2759184

Proving, once again, that the gap between theory and practice is larger in practice than it is in theory.

The requested URL /metingen/measurements.html was not found on this server .. http://www.xs4all.nl/~cp4trml/metingen/measurements.html .. any other publications ore sources out there?

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___/\___/\___/\___ the s u r f b o a r d of the K u r p f a l z is the r o a d b i k e .. oSo >>

Schreuder's pages seem to have disappeared; I can't find them even on the Wayback machine. But the Chung method should get you to the same place, if you're trying to get to rotational drag from Chris' hint. That's just my opinion since I haven't worked out the trick. Viel Glück!

I'm always shocked , ok not shocked, by how closely bunched the transitional drag numbers are for different 'aero' wheels at 0-5 deg yaw.

Differences between set ups appear usually only at higher yaw angles

Is there some kind of inherent min at 0-5 deg yaw ?

Does nothing behind the leading edge really matter at 0-5 deg and hence "they" all are very closely matched ?

Chris,

I'm moving to disc brakes as we speak & your release couldn't be more timely. I've asked my LBS, who tells me you've already got these in stock, to grab me a pair.

What kind of overall penalty will I pay with 26c Turbo Cottons? The Crr would be slightly better and the aerodynamics a bit worse, correct? Given the 29.5mm width of the rim, I'm hoping it's still a very fast combo.

I'm a road & crit racer chasing that Cat 1 upgrade this year. The increased comfort and grip associated with a wider tire I can run at 10% lower pressure is (wholly subjectively to me) substantial.

Also, has anyone tested the Crr of the S Works Turbo tubeless? It'd be more aero than a Cotton, right? Still a very fast tire, I'm guessing? Again, for my discipline, the extra flat resistance could be totally worth a small enough resistance penalty.

Congrats on the new product release!

We should compare aerodynamic torque results some time between my 6 component axis data and your method.

If I had access to a tunnel that didn't have a 6 component balance and wanted to back my way into aerodynamic torque, I'd pursue this setup:

http://www.biketechreview.com/...w_negative_watts.wmv

then do sweeps on starting coast down speed and wind speed all while measuring rotational speed and axial force as a function of time (#3 on the list here). One ought to then be able to calculate/model bearing torque, moment of inertia, and aerodynamic torque...am I close?

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Kraig Willett
http://www.biketechreview.com - check out our reduced report pricing
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Good work Specialized. Pretty amazing stuff. Glad to see a bike company reporting the whole picture.

So you tested the Turbo Cottons as the overall fastest combo among those two tires, but what about competitors tires such as the: Supersonic, Attack, GP4000s, and Force?

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