same principles apply to the speedo swimsuits used at the olympics

The Speedos are dimpled/rough? Methinks I'm gonna have to go down to the pool and take a little survey...



So why is the famous Yamamoto wetsuit rubber all slick then?

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<If you're gonna be dumb, you gotta be tough>
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maybe speed has something to do with it---perhaps a swimmer cant get fast enough to receive the benefits of a dimpled wetsuit. I have one of the Speedo Aquablade suits---im not sure if its faster cause its microscopically dimpled. I never noticed any dimples on it.

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Want: 58cm Cervelo Soloist. PM me if you have one to sell

Vintage Cervelo: A Resource

I thought the Aquablade stuff had those textured stripes? Of course, I thought the dimple effect was for spinning applications too, but I know precious little about aerodynamics, hydrodynamics, thermodynamics, and female dynamics.

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<If you're gonna be dumb, you gotta be tough>
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>there in an other idea behind the dimples and it has to do with hydrodynamics. When airflow goes over a >surface it is the molocules of air rubbing over the molocules of the material, dis-similar surfaves, hence >drag.If you rough up the surface, some of the air molacules get trapped in the "holes", thus you have air >molacules rubbing against air molacules yielding less friction. Before doing tri's I raced sail boats, we would >fair our hulls with 800 grit sandpaper to get the same results.


This is the principle behind the new Zipp wheels also. It works in air similar to water. Certain aircraft designs are also starting to take advantage of this. Helicopter rotors come to mind as one part that has used this to advantage. More speed and less resistance to turning puts less stress on the engine, let alone the performance advantage. That is why I think we'll see someone try this with bikes in the near future. My thoughts, though, remain that the relatively low speeds we travel at on bikes make the performance gain more or less negligible. Unless you need 4-5 seconds to win the next 40k TT ;P

While I can't comment on the aerodynamic advantages of the dimple effect, I can tell you they provide a substantial sales advantage as we have sold two of these new wheels during the past two days. People seem to be quite excited about these.

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Tom Demerly
The Tri Shop.com

Francois,

I can´t believe you said that Colnagos are made in Taiwan...

You are SO WRONG !!!!!! I went to their manufacturing site in Italy, and I can tell you, if is there any Italian on this FORUM maybe he didn´t answered you because he had a heart attack when he read your message.

COLNAGOS´S ARE EXTREMELY GOOD AND MANUFACTURED IN ITALY !!!!

Colnago is part of the history of Cycling !!! I don´t know what is your background in Cycling but definately you need to learn a lot about Colnago´s.....

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Luiz Eng

you went to their assembling site in Italy..
the info is a very reliable source, and an italian source.
My background is 3 years cat 1 in Europe, I know cycling pretty well, and colnago are not made in italy anymore for some years. They are finished and some of them are painted in italy.

now, believe whatever you want, If you feel better believing they are made in italy, then believe it...
Check also the italian law on what are the rules to claim "made in italy" label...you will be surprised.

...sigh...What geeks we are...can we get back to Kate Winslet and her dimples...It's cold and snowing...I need something better than aerodynamic profiles to get me through the winter.

All this tech talk is making my Seasonal Affective Disorder worse.

Dan :)

dan. is it your belief that kate winslet's dimples cause her to be more slippery? do you have proof of this? or, are we saying that in the case of ms winslet anecdotal reports of slipperiness and/or dimples is sufficient ??

To misquote the worlds most profund philosopher Homer Simpson.

"AHHH. Dimples. . . What can't they do."

[reply]Gerard's the man to talk to about this (not me), at least this is the impression I've gotten from reading about his bicycle designs and talking with him personally.

I was really impressed that he used NACA data, and therefore a NACA airfoil for his bikes. (I'm a grad student in the aerospace department at the University of Michigan, so I get off on stuff like this.) [/reply]


While NACA is a good start, it is by no means the final solution for aero shapes at cycling speeds. Our first tubes were exact NACA profiles, but we have moved more and more to "modified NACA" shapes or completely free-designed shapes. NACA was never too conerned with the Reynolds numbers of bike tubes but with way higher numbers, and they definitely had no interest in the flow coming off a front wheel onto a fork leg. So you really need to do some development to get a very good shape. The cool part is, you get to name your own profile (as we did with the shape of the Wolf fork), sort of like discovering a new star.

The same would also apply to a crank, which has to be aero in two directions as even on the bottom half of the pedal stroke the crank is still going forward relatively to the ground. But the real question is, who is willing to spend $50,000 to find a better crank shape? For most companies, that money will more likely go to advertising promising a better shape than to research to actually find a better shape.

Gerard.

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Gerard Vroomen
3T.bike
OPEN cycle

Thank you gerard for your input. You guys have done a lot of interesting work.

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"What the mind can conceive and believe, the mind and body can achieve; and those who stay will be champions."

This is an interesting theory. However, I question it a little for the following reason. When air flows past an object, such as the skin on a wing, there can be no slipping at the skin surface, by virtue of friction. In otherwords, the air molecules directly adjacent to the surface are stagnant (or trapped, as you would say). So there is a zero velocity condition at the surface, which then goes from zero to free stream velocity as you go through the thickness of the boundary layer. So, even with a perfectly smooth surface, you still have air molecules rolling over air molecules.

I agree that roughing a surface (or adding dimples) could have positive effects on drag in some instances, however, I question the explanation given here. Futhermore, drag is merely a retarding force made up of many different components. I am not sure that the major component of drag is always (or ever) due to skin friction on non-aerodynamic objects. There are other things, like pressure drag (in the instances that we deal with on bikes), that play a bigger role. Like a golf ball, where the separation, and subsequent suction, on the back half of the ball is very large, therefore a little skin drag is added by the dimples since this makes the flow stick more the golf ball over the back half and thus significantly reduces the area of suction. This is the same reason cervelo uses aero tubes. They increase the surface area (and thus skin friction) but they greatly reduce the amount of separation present on their tubes.

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"What the mind can conceive and believe, the mind and body can achieve; and those who stay will be champions."

That's pretty interesting and high tech stuff Zipp is doing, I can't even imagine the flow going over the rear wheel of a bike. I still don't understand how the dimples would help in this case, but that may just be because I am stuck in all this golf ball and skin suit way of thinking, and they just apply to rotating wheels differently. Like I said, I don't have any idea what the flow is doing on that rear wheel, so I can't really understand why Zipp did what they did, but if they are seeing these kind of results, they are doing something right. I look forward to finding out more as people start really riding these wheels and looking at them closely.

Also, thanks for the article, it does a better job of explaining this stuff than I do.

This was a real interesting thread to me, I hope no one got annoyed.

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"What the mind can conceive and believe, the mind and body can achieve; and those who stay will be champions."

[reply] Futhermore, drag is merely a retarding force made up of many different components. I am not sure that the major component of drag is always (or ever) due to skin friction on non-aerodynamic objects. There are other things, like pressure drag (in the instances that we deal with on bikes), that play a bigger role. Like a golf ball, where the separation, and subsequent suction, on the back half of the ball is very large, therefore a little skin drag is added by the dimples since this makes the flow stick more the golf ball over the back half and thus significantly reduces the area of suction. This is the same reason cervelo uses aero tubes. They increase the surface area (and thus skin friction) but they greatly reduce the amount of separation present on their tubes.[/reply]

Correct. The idea is not to minimize skin friction, but the size of the wake behind the tube/wheel/rider, and "roughing" the surface would be a way to make the boundary layer turbulent, therefore giving it more energy and allowing it to follow the shape of the object longer. Thus the flow doesn't detach at the widest point of the tube but further back. consequently the wake is also smaller. This is one thing we also found with some "aero" forks on the market, they are bladed and deep but the shape is so bad that the airflow still detaches early so the wake is huge (and deep) resulting is pretty mediocre drag numbers.

That said, with a proper shape it may not be necessary to rough the surface. We tested our new fork with and without all sorts of add-ons to change the surface, but nothing made it better than the "plain" version. Also, just adding dimples isn't a guarantee for success, I don't think the dimples on the Troxel helmets did too much.

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Gerard Vroomen
3T.bike
OPEN cycle