Fake? I think you're really being pedantic if you don't think Trek is using a kamn tail profile in the Speed Concept. Btw, there's a reason nobody wants to test/benchmark against that bike: it's fast. It's really really fast. *AND* it's really really fast across a wide yaw sweep.

Some of the Trek bikes may be an exception but I laugh every time people say kamn tails are superior. Have you guys never heard of frontal area? True teardrop aero foils beat the snot out of even true kamn tails. We had that post from the previous thread on this topic that you have 30-50% more drag on a kamn tail than a tear drop aero foil simply due to turbulence. It's not even in the same ball park.

And Trek's TT bikes are not exactly winning any TT races.....

I'm on the third generation of the propel brakes and they're still poor to middling. They still have clearance issues, need very regular maintenance and lead to lack of confidence. Changing brake pads from the lousy TRPs improves performance immensely - from awful to just about ok. I've spent dozens of frustrated hours tweaking these brakes and have to do a check on them before every ride. I have never had a single problem with any standard rim brake caliper.

Probably the Fouriers work a bit better but don't see why I should have to invest a couple hundred dollars extra to get acceptable braking that should have been there in the first place. It's not a given that they do work better than the current TRPs.

That was the first thing I noticed. The size of the tunnel is small an probably has significant blockage issues. Also they tested out to 30 degree. The did their own weighting and said they were ~ equal to the competitors. Umm... Ok.

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Heath Dotson
HD Coaching:Website |Twitter: 140 Characters or Less|Facebook:Follow us on Facebook

How do you put a bottle on a downtube with a tear drop shape? Design is about compromises.

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Kamm. As in Wunibald Kamm (1893-1966).

How do you keep fucking that up? It's like reading an argument from someone about why a Camero [sic] is a better car than another, or watching somebody ski in jeans.

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Eliot
blog thing - strava thing

Road bike or TT bike? If you are going full aero, every one knows you don't use round bottles.

Levis and Scotchguard 4 LIFE!

I think it's much more natural to spell it as kamn. Just look at how the other people in this thread wrote it.

Speaking of which, why aren't disc brake calipers kamn tail shaped for improved aero?

4 LIFE!

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Eliot
blog thing - strava thing

I see, so for you, being wrong is much more natural. :)

First instance of "kamn" here is yours.

Maybe a good answer to your question is that that's something to be optimized later, but ironically, that won't happen unless there's a space in the market for disc brake calipers that are going fast. So it's a bit of a chicken and egg problem?

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Eliot
blog thing - strava thing

Here is an image from a science study showing how a Kamm Tail is so much worse than a tear drop aero foil:


http://imgur.com/Z7hNNb3

Notice that the bottom most Kamm Tail is what is used on today's so called aero bikes. That shape has 5.6 TIMES the drag of the tear drop! Kamm tails suck! And you guys are just buying into the marketing, worshipping Kamm tails, without actually looking into the science.

I don't think anyone is disputing that a truncated aerofoil experiences more drag than a complete one. Chopping off the back-end is an engineering compromise, offering benefits while still retaining advantages over traditional (round) tube shapes. Round by the way, is what you should be comparing a truncated shape against.

Also, the aspect ratio of an aerofoil is important both in terms of drag and its structural utility. The one in your link is impractically high for a bike frame, as whatever shape is chosen must also be able to offer rigidity in multiple planes and represent some kind of optimum between weight and stiffness.

Some people here seem to think that a Kamm Tail has virtually the same drag as a tear drop. That is completely false as can be seen by the study image. A Kamm Tail is many times worse in drag than a tear drop. Why do you say I should be comparing a Kamm Tail to a round tube? That makes no sense to do.

And there is nothing impractical about that tear drop shape in that study. The bikes of the 90s were made that way until the UCI brought in the 3:1 aspect ratio rule. You are just another one of those people who have drunk the Kamm Tail koolaid and believe the marketing material.

Does the above extract not refer to cylindrical volumes? I believe it does. It's primarily relevant to aircraft fuselage shapes, not airfoils. This is not applicable to wings or similar surfaces such as bike tubes.

You seem to have decided aerodynamics, and engineering are trivial and obvious. You are wrong. You seem to believe design involves a right and wrong answer. You are wrong. Design is about compromise. Anyone who thinks it's not, doesn't have a clue what they're talking about. You keep telling people they are fools.....I have my own suspicions.

How in the world did you warp the meaning of that study image to mean cylindrical volumes when it is clearly labeled as drag numbers? And your denial that the results are not applicable for other areas is laughable and sad.

It is trivial and obvious that Kamm tails in the bike industry are just a marketing term when tear drop shapes tubes have always performed way better.

Please explain the use of the term fuselage and the inclusion of a circular cross sectional image on the sketch if this is not for cylindrical bodies. I think you'll find my interpretation is correct but I'd be happy to be corrected if I am in fact wrong.

The circle in the images are so that you can see the airfoils line up and provide a point of reference, not because this is for cylinders. SMH. I don't even know how you could even think that. What is the point of the tear drop and Kamm Tail shape outlines then?

And the values given are Cd numbers, meaning it is valid for other uses, not just aircraft fuselages. Do you even realize that virtually all the airfoils used in the bike industry come from the NCAA testing done for aircraft?

For starters, it's NACA, not NCAA.
And yes, I'm very familiar with NACA airfoils. More so than yourself I dare say. Most of them are rather old by the way, from the first few decades of aviation. There are better airfoils for most applications but NACA airfoils are still a common point of reference and are still useful for non-critical applications. Anyway, NACA airfoils seem a little off topic here, in what's already an off topic discussion, so back to the issue at hand...

Apologies if my use of the word cylindrical caused any confusion, perhaps if I used engineering terminology and called them surfaces of revolution you'd understand what I mean?
As I said earlier, your comments thus far lead me to believe you consider this subject to be simpler than it is. It's a commonly understood phenomenon that incompetence breeds confidence and overestimation of ones own ability. I think that's at play here (Refer to the Dunning Kruger Effect).

Airflows are complex and that complexity matters. A two dimensional airflow over a simple airfoil is not the same thing as a three dimensional flow over a surface of revolution. You've introduced to the conversation, data which refers to the latter. You appear not to understand the very material you are trying to use to support your argument.

I'm not sure what you mean about Cd values "meaning it is valid for other uses, not just aircraft fuselages". Can you explain what you mean?

As for the bits I've highlighted in bold. I suggest you try and restrain your condescension until you've made quite sure that you're the one who knows what's going on.

Yep, spot on.

What is your background in aerodynamics?

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Is that question for me or Hybridlete?

+1 for reference to Dunning Kruger effect!!

I've seen enough weird things in wind tunnels to agree that this stuff is not simple...and can often be counter intuitive. Anyone who tries to simplify it and add an air of condescension is misinformed or trying to mis-inform.

Hybridlete

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Make Inside Out Sports your next online tri shop! http://www.insideoutsports.com/