Fat Airfoils and HED

Mark V
16 years ago
Categories: Blog

I’m a big Mavic junkie when it comes to wheels. I have 3 sets of Mavic Classics floating amongst my bikes because I like the ceramic rims and the beautiful simplicity of their hubs. So it takes a lot to bump me off my Mavic aerowheel, the Cosmic Carbone. But after playing with Byron’s Hed wheels, looking at Hed’s data, and reviewing old reference materials, I’m convinced that Hed’s are the way to go.

One of the career tracks I almost took was aeronautical engineering, so I actually have a strong understanding of the principals involved in designing a aerodynamic wheel. The whole gist of Hed’s “C2” 23mm platform is that a well shaped rim/tire combo is better than a rim that has less width than the tire.

The Mavic Cosmic Carbone has a very pointy fairing attached to the aluminium rim compared to the Jet6’s blunted fairing; the Cosmic looks faster than the Hed. But it isn’t, especially if the apparent wind isn’t directly from the front. The reason is that the key to low drag is getting the wind to flow smoothly over the leeward side of the rim. The Jet’s shape allows the air to flow over the tire onto the rim without “tripping” over the tire/rim interface. That way the airflow stays smoother and faster over more of the leeward surface of the rim and at greater angles to the wind than aerowheels based 19mm wide rims.

At the speeds a bicycle travels, the ideal shape is surprisingly blunt and rounded. A lot of people assume that bike equipment that looks like it came off a MiG fighter must be fast, but a bike never even approaches the air speed which is necessary to keep a fighterplane from falling out of the sky. Airflow at that speed just doesn’t behave the same as a transsonic aircraft, so the structures wouldn’t have the same shapes. In many ways bikes have a lot more in common with high performance sailboats than they do with airplanes.

I just got a set of the C2-type Jet6 wheels. Unfortunately, I have some major traveling to do in two days, so I may not be able to give a real riding evaluation till next month. One quick ride did reveal that the 60mm tall Jet6 handled crosswinds distinctly better than the 52mm tall Cosmic Carbones. The rear wheels are within 15gr of each other, favoring the Jet. More riding impressions next month.

see below: Mavic Cosmic Carbone

Compare to Hed Jet6. The sidewall label is less visible because the tire doesn’t overhang the rim on the wider C2-type Hed wheel.