I saw this article this morning and it made me think of this thread...I thought I'd put this "nugget" here:
Quote:
Disc brakes, in their current incarnations, aren't aero. I'm sure we all guessed that. The magnitude of the difference is fairly significant.
"We've measured a 16% increase in wheel drag between a disc-braked wheelset and a standard wheelset", Jean-Paul told us. "We performed a direct back to back test of the Zipp 303FC in standard version and disc brake version, for our own competitor comparison purposes. That 16% is a constant offset in the performance curve across the entire cross wind angle range."
So there's work to be done there, but how much can actually be done? The extra drag essentially comes from three sources. The rotor itself adds drag, and because disc wheels need more spokes to cope with braking forces there's more drag there too. On top of that, a disc hub contains more material and needs to be built to withstand torque across the hub body, as the braking forces are on one side only. Because of that, the hub body is generally bigger and that increases drag as well.
What can be done about those three sources of extra drag? In reality, probably not a huge amount, and disc systems will likely continue to be at a disadvantage in terms of aerodynamics. So if you want to be as slippery as possible, it's rim brakes for the time being. And hide them, if you can.
- See more at:
http://road.cc/...sthash.UqlZlf29.dpuf
http://bikeblather.blogspot.com/