Fat Airfoils and HED

IMG_6284.jpg 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

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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.

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6 Comments

You guys are giving me expensive ideas. Keep it coming.

Mark,
I see 24” HED wheels on a Bianchi mini-velo in your future.

Tai

As a Minnesotan and regular passerby of Steve Hed’s old shop, it’s hard to choose anything else.

As a non-racer and general cheapskate, I don’t get near this kind of hardware.

As a cynic, I have a few thoughts about this wheelset, based on nothing but opinion. 

First off, don’t forget that Zipp, EDGE, and a few others have dogs in this fight, but if we’re keeping it strictly with aero wheels with amateur practicality (aluminum clincher rims), the C2 Jets are a nice choice.  They are at the top of my wish list, in fact.

We can take it on faith that the wide rim profile is more aero and increases the tire contact patch for better handling, but that necessarily transfers at least some of the drag lost in the wind tunnel to drag on the pavement itself, perhaps even more so with tires that claim to use higher traction compounds on the edges of the tire surface.

The wide rim and deep section sound like a dream for CX, but road tubeless is gaining a lot of popularity in this area, too.  At fancy-wheelset prices, why should anyone have to choose?

aerodynamic drag is the dominant obstacle to a bicycle at a racing speed unless it is a steep climb. rolling resistance is in the form of the slightly greater area of exposed soft traction compound (on the tread of dual compound tires such as the Michelin Pro Race) would be way down the list of contributing factors. 

also, at least one study (not HED) suggests that wider road tires yield less rolling resistance for any given air pressure than narrower tires.

from what i understand, the type of gig used for testing rolling resistance can greatly affect the results.  I haven’t really read enough about the varying methods to have an informed opinion on what data would be most relevant for comparing rolling resistance of various tires/widths, but most studies comparing aerodynamic drag to rolling resistance rank rolling resistance way below in importance.

@Tai

actually, the Bianchi Mini Velo takes a 20x1-1/8 (451) rim, so I’m not sure if Hed makes that size.  anyways, for that bike I’m more interested in the Schmidt Son 20R lightweight dyno hub for 16/20” rims.

maybe i’ll finally get a Mini Velo in Japan, depends on how flush i feel when i get to Tokyo at the end of the month. Japan ain’t cheap and them Hed wheels weren’t free!

Reading VeloNews, it’s clear that rolling resistance measurements are extremely controversial, but in an industry full of so many subjective and distorted claims, it never hurts to do a little fact-checking.

I hear 29” deep section wheels are getting just as popular in cross-country, for the same reasons they are in ‘cross—maybe I just made that up, but you can make it sound logical.

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