The marketing supports this:
- Easton video
- Zipp 404 Firecrest Carbon Clincher promotional drag chart
- Flo Cycling (buzzy start-up that promotes a “Net Drag Reduction Value” weighted toward drag at 10–20° yaw angles, which they call the sweet spot).
What’s more, at low yaw angles the bulbous wheels aren’t significantly faster than old-fashioned ‘V-notch’ aero wheels. Sometimes they’re even slightly worse in wind-tunnel tests.
•••
Slowly it dawned on me that, although the wheel companies talk a lot about high yaw angles, I very rarely draft other cyclists at such high offsets. Usually the best position to draft is almost directly behind. In other words, high yaw angles are rare in my own cycling.
So I tried to find some information to back up my feeling that high yaw angles are rare. I came up with this recent PDF paper by Catalyst Cycling, another start-up.
I didn’t follow all the maths, but the bits I did follow certainly supported the devastating conclusion:
“The main conclusion that can be drawn then is that wheels should be designed for much lower yaw angles than those that are currently being used. This means using narrower tires and narrower rims, as well as less bulbous rim shapes.”
Doesn’t this suggest the current trend toward fat, bulbous rims and wide tyres on road bikes is, charitably speaking, misguided?
•••
On a related note, this Tour de France I noticed that Richie Porte and Chris Froome, riding for marginal-gains Team Sky, often use shallower rims than the competition. The exception appears to be on stages with a risk of crosswinds (high yaw angles) and echelons, when Sky breaks out the deep-section rims. (Of course the review websites would tell Froome he needs shallow-section rims in crosswinds, supporting my extreme suspicion they aren’t worth reading!)
All very interesting, isn’t it?