which bikes, and where on the down tube. Some have some funky shapes.

Also, why??

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Yaqui, check it out Joe

If you are going to make people get out their calipers, get aspect ratios as well!

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I'm actually surprised how small/narrow the downtubes are on my (sold) P2K and Lemond carbon/steel compared to most bikes out there.

I'm actually amazed how fat downtubes are on most carbon high end road bikes. The only thing slower than a round tube is a bigger round tube. And the only thing slower than that is a big ovalized tube that most of the high end carbon bikes have. The Cervelo R3 even has a rectangular downtube. How do you say "as aero as a brick".

Even a number of the high end carbon tri/TT bikes on the market have bigger dimension tubes that probably aren't near as aero a design as the smaller Cervelo aluminium tubes on the P2K or P3.

Aero tubes for mass start road racing?

I like the Soloist, it makes sense, but the best aerodynamics in road racing ... is drafting

:)

Aero in road racing is not generally considered that important, but an aero fame certainly can't hurt. Consider that most of the TDF riders this year were riding deep 50ish mm rims. So why if aero doesn't matter?

On a breakaway an aero frame might help a bit. I'd rather be on a breakaway on a Soloist than an R3.

I use 50mm wheels for RR's and crits, wheels matter more than the frame. Other than the Soloist, I can't really think of another mass produced aero road frame.

OK, i know you all have taken the calipers out and are ready to report back to me. don't be shy. especially those of you with P3's, Kalibur's, B2's, and DA's.

Cervelo P3C 29x81 = 2.8
Cannondale Slice 31x79 = 2.5
Specialized Transition 30x74 = 2.5
Kuota Kalibur 80x80 = 1 (estimated ;-)

All measurements to nearest mm on calipers (and not clasping too hard as I dislike scratches). Cannondale has external cables and Transition has no paint so add ~1mm for normal. P3C has the sharpest trailing edge

Was at the LBS so stole their calipers and had a walk around.

Orbea Oro 40x75 = 1.9 (Ordu is same)
Scott Plasma 45x74 = 1.6
Kuota Kalibur 38x72 1.9

So my estimate on the Kalibur was a bit out, the tube is box shaped so aspect ratio means little. Oro is plain oval shape and Plasma is flat sided and rather plump tear drop.

Not looking good for the carbon frames at the moment - only one has a narrower DT with better aspect ratio than the Ally frames I measured.

Felt S32 27.5 x 71 = 2.6

Hooker Cat. 1: 22 x 66 mm (3:1).

I just checked my Cervelo Dual and it measures out at 28mm X 75mm. After reading the replies and looking at most bikes (sans hooker) the Dual is like a knife. Very narrow.

Do we have a winner?

You're going to make people doubt their carbon frames if you post numbers like that, shame on you.

"the Dual is like a knife. Very narrow."

That's my point about my old P2K. I don' think many besides Cervelo (except the Hooker) is getting close to the 3:1 ratio that is optimal for aerodynamics. A few are, but a lot of the "aero" frames aren't all that aerodynamic.

Are you measuring the depth of the down tube on a plane parallel to the ground, or just perpendicular to the length of the tube?

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Well you have to keep the 3:1 ratio in perspective correct? It is not good if you have say a 35mm X 100mm vs a 27mm X 78mm and it is not a wing shaped profile. I think there are a lot of 3:1 bikes out there but they do not get as close at Cervelo has to the 3:1 aspect.

claimed to be the new Planet X aspects http://weightweenies.starbike.com/...ownload.php?id=14776


so I get 1:1.84

perpendicular to the length of the tube

So the aspect ratio of the tubes generally exceeds the 3:1 ratio, then, when you look at it from the perspective that the wind sees.

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Correct, but if it's not a true airfoil in major/minor axes it has no chance of being aero from the winds perspective.

If we take an 80mm DT at an angle of 48deg (from the PX diagram referenced above) then the length horiz to the ground is 95mm so with a 30mm minor axis the ratio goes from 2.7 to 3.2. Obviously those frames that were scoring below 2:1 are not going to get to 3:1

Yaqui Carbo 29 x 59

If aerodynamics is a factor of Frontal area and shape(coefficient of drag), where is the compromise?

What I mean is, is a tube of 30x60 thats not that well shaped, faster or slower, than a 40x80 that is well shaped?

No, but the ones that are in the 2.5:1 range are pretty close. I just wanted to know how the measurements were done so we could know if there was any additional interpretation needed.

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