You can use my Softride TT7 but it is large size not medium.

I can tell you the results of the test already:

Second place - The Cervelo P3C

First place - Everything else..............


Hugh Blake

Moving along on this as fast as possible.

Looking at the sourcing of bikes with regards to issues of size, spacer stack and proprietary cut-to-fit seatmasts, I have decided to go right to all the manufacturers first and see what they have to say/contribute. Expect to see a wide range of responses there.

As this has really snowballed in the last 24 hours, I will say again, this will be done right, or not at all.

Dave Luscan

I wonder which marketing departments have already started working overtime to come up with excuses!?!


I've been thinking about this.

I'm beginning think that the effect of extra spacers above the stem won't actually be that bad as they would follow the basic aerodynamic drag equation fairly closely so could be calculated out (although this calc would need to be shown obviously).

The additional spacer stack will be above the stem and thus at least that far above the top tube. What that means is that it will be dealing with slightly messy air off arm rests etc. but the wake won't strongly interact with the top tube or any other part.

I should point out that I'm assuming that the vertical component of the velocity won't be adversely affected by the angle of the spacer stack.

Otherwise, I agree with MIT's points.

I've been trying to work out how to get more money for this test. Is it possible that you could get sponsorship whilst keeping the test impartial? Sponsorship from a wheel or component manufacturer? The tunnel themselves? A magazine who aren't interested in pandering to the manufacturers?

One other thing might be interesting to throw into the mix since you are going to all this trouble. When you are looking at aero helmets throw in a look at their cooling ability. If you are going to use a standard manequin it would be easy to put a thermocouple on a moist head and see where the temp leveled out at below ambient in the tunnel. This would give you a good indication of the relative cooling ability of the various helmets.

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Frank,
An original Ironman and the Inventor of PowerCranks

That's a seperate study entirely. We've tested this on a mannequin and subject in >30deg heat conditions, and found no difference between a regular helmet and an aero helmet with vents uncovered.

Xav

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AeroCoach UK
http://www.aero-coach.co.uk

Where are your results and protocol?

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Frank,
An original Ironman and the Inventor of PowerCranks

In a drawer. This is off-topic

Xav

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AeroCoach UK
http://www.aero-coach.co.uk

What helmet did you use. I find it hard to believe that no wind and wind yield the same temperature.

Maybe . . . hopefully . . . possibly I am wrong, but I will be AMAZED if you get any cooperation from the manufacturers.

Most of them have an active self-interest in NOT having independent data made available. My guess, if the manufactures aren't in control of the test protocol and the presentation (read manipulation) of the results, they will want no part of this.

Again, hopefully I am wrong. But I doubt it.

I remember an older study, but wouldn't be able to put my finger on it that came to the same conclusion. I believe A Coggan has mentioned the same study, he may be able to put his finger on it.

Styrrell

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Styrrell

While I agree that the drag on the spacer stack itself can be characterized decently well via test or simulation (I am not aware of any basic aerodynamic drag equation for a non-infinite shedding cylinder....unless you are thinking about empirical fits/models on tests of similar geometries), I think the bigger issue is the interaction effect with the rest of the bike. Although (as you pointed out) this effect is very small relative to the absolute drag on the spacer stack, it may or may not be negligible relative to the drag differences among different bike frames (the original question we are trying to answer). It sounds like you know what you are talking about, so I'm interested in your thoughts (perhaps I'm emphasizing a level of precision that is completely unnecessary...). Also, as a practical point having extra spacers above the stem may make it harder to compare with bikes like the Shiv/Trek Speed Concept where this is not possible....whereas spacers under the stem can at least be comparable (in terms of real world setup) to arm pad spacers.

Also, I wanted to ask anyone that knows: What is the data acquisition rate on the force balances in question and what is the typical sample duration?

Chris

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Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc

Then, my comment stands. Perhaps he should consider adding this to his protocol.

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Frank,
An original Ironman and the Inventor of PowerCranks

Isn't it a rule of thumb that about 25% of the bodies cooling comes from the head? There are three main methods to transfer heat to cool the body: conduction, convection, and evaporation. The helmet could alter all three. Seems unlikely there would be zero difference between helmets, let alone between a standard helmet and an aero one.

I would like to see the protocol and to have it confirmed before I "believed" such a result.

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Frank,
An original Ironman and the Inventor of PowerCranks

Perhaps in a free convection state...but, what about forced convection?

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http://bikeblather.blogspot.com/

As I think about it the amount of cooling in the sweating athlete due to the head is probably less than 25%, although the head still probably contributes more than its fair share based upon surface area considerations alone since it is so exposed to the wind relative to other body parts, usually (unless encased in a poorly vented helmet perhaps).

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Frank,
An original Ironman and the Inventor of PowerCranks

My thinking was based on the idea that by looking at a stem with a steerer cap, you're already looking at a cylinder with one end (the bottom end is integrated into the bike). Even with only a stem, there will still be a top end to the cylinder. I'm not suggesting removing a non-infinite cylinder [by calculation], I'm suggesting removing a small infinite cylinder from an exiting non-infinite cylinder.

The bit that will cause errors is the air flowing down after going over the top of the steerer top cap. I'm making the following assumptions about this flow:

a) The vertical component of the airflow behind the stem is near 0 when it reaches the top tube. This means that we won't affect the airflow around the top tube by adding a spacer stack.

b) That the vertical airflow passing over the steerer cap and 'dropping' into the wake of the stem is damned nearly the same as the vertical airflow dropping into the wake of spacers.

If either of those assumptions are wrong then ignore the idea; it's much more difficult to remove a chunk of cylinder by calculation.

Edit #7 - Dang, the Spec Transition with it's top tube fairing of the stem is number 8 on the list of bikes to test. That would be essential test without a spacer stack on top of the stem.

Edited several times to make my thoughts and words correlate!

BTW Dave, big kudos for attempting to do something that (almost) everybody on ST says should be done, but hasnt attempted.

Kevin

 The "First Annual Slowtwitch Wind Tunnel Shoot Out" has a nice ring to it:)

Slowman?

-Scott

Ah, I see what you are thinking. I was imagining that the flow leaving the stem with a top cap (ie; no spacer stack) was more akin to a trailing edge flow (treating the cap as part of the stem 'fuselage', and the stem as a slender body). If this is close to reality, a spacer stack would substantially modify the flow field to one of a shedding cylinder tip. Again, I am just poking and guessing here since I have no direct experience with flow fields on a bike (this is the cue for Mark to jump in with his expertise).

Putting aside the fluids babbling, I'd like to add to the praise that Dave is getting for taking on a project of this size. Let's hope it all works out....

Chris

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Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc

LOL

I guess you beat me too it. One of the reasons the head is a bigger sink under normal circumstances more blood flow goes to the head. When exercising the limbs will tend to vasodilate as you start to sweat so, it would seem the percentage loss from the head would drop.

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Frank,
An original Ironman and the Inventor of PowerCranks

Hey Dave, kudos for your ambitions to address a hot and sticky topic...as indicated by the Slowtwitch buzz/firestorm.

As a small manufacturer I've had the same dream, but lacked the resources to bring it to life.
I'd be honored to have a TitanFlex in the game. Just let me know when and where to ship the new stretch model.

Acknowledging the difficulty in normalizing for the proprietary aspects of individual frames*, I trust your judgment in constructing a test protocol that is transparent and impartial. I also appreciate how tedious/costly it would be to satisfy everyone's pet concern. That said, here are my suggestions:

1. Because you're not testing saddles or seatposts I like the idea of attaching a "blob" to the saddle/seatpost.

2. I also like the idea of standardizing the stack height. If need be, put stack spacers under stem. Maybe just make the elbow pads the same height above the ground/bottom bracket. In the interest of simplying the set ups, I'm okay with using a standardized front end "blob/nosecone" as well.

3. As one poster mentioned, forks should also be normalized--to something close to the Shiv's if it is tested. TitanFlex uses a 1" steerer and I would be happy to include an Easton EC90 Aero fork you could cut down.

4. For obvious self interests, I question the inclusion of frames no longer in production (Lotus, Hotta, Zipp, etc.)

That's all I got for now. I'll continue to follow the thread, where considerable expertise has been showcased...along with a few distracting/obnoxious posts (par for the course).

Cheers,
Tom Piszkin
UCSD Masters Triathlon Coach

*The P4's integrated water bottle comes to mind. I can imagine Cervelo designing a test that required all frames to carry water! A TitanFlex sponsored test would require all bikes to be tested with riders sustaining an aggressive aero position for 3 hours while somehow simulating rough roads.

Disagree on a universal fork. I designed the 4000 and the Airfoil fork to work directly with the frame.

This is where wind tunnel data is subjective.

The goal with Kestrel is to match fork, bars, post, etc together to make a fast BIKE, not just the frameset.

To get fair data, the complete bike as presented to the customer should be tested, and really a rider should be in place to see how the complete unit (bike and rider) work together.

None of the bike data matters if the complete unit isn't tested.