Speed & Aero or why drag a boattail around at 45mph?

[Xist]

Please explain which way that tube is pointing. I cannot tell if the flat or tapered side faces forward.

[jeff88]

On most of those new bike frames (that I've seen), the taper is forward facing. I wonder what flipping it around would do for a biker (especially a racer).

[HypermilerAX]

I'm myself a cat 2 racer. On a traditional bike, the last thing we're looking at is aero as most of the drag is coming from our position and aero effect is much reduced when drafting. We're looking at weight and stiffness. For individual efforts, time trials bikes are used. Heavier (17 lbs) but more aero.

[COcyclist]

Originally Posted by orange4boy

Too bad they didn't test that tube profile the other (better) way around.

Trek designed a carbon fiber bike with similar profiles (although more of a full Kamm shape) to be more aerodynamic in crosswinds.

"Unlike a conventional airfoil, the KVF tube shape retains full aero benefit at yaw (crosswind). The virtual tail bends to maintain its aero shape in the presence of the most prevalent crosswinds. The virtual-tail truncated tube shape allows us to use less material, for a lighter yet stiffer frame."

Crosswinds are significant at the lower speeds of bicycles. A car or motorcycle going 60 mph will be less negatively effected by a 10 mph crosswind than the bicycle.

Speed Concept 9 Series - Feature tour - Trek Bicycle

Click on KVF tube shape.

That said, aero drag is pretty significant at 30 mph or even 10 mph with a 20 mph headwind. Ask any cyclist.

[Xist]

If you are riding 30 MPH forward, then the wind is already pushing 30 MPH against you. If you have a 10 MPH crosswind, exactly what are the forces against you? Can I use the Pythagorean Theorem? 30² + 10² = 31.6something?

That is 5.4% more air resistance.

That is enough to be irritating.

I do not understand how you could make a shape aerodynamic for 270°, winds and cross-winds, I would think that you would make compromises.

[kach22i]

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