Found an interesting article about Dr. Teddy Woll, head of aerodynamics at Daimler. There's no date on the piece, but judging by the absense of discussion of the
Cd 0.24 E Class coupe, I'm guessing it's older than this year.
He talks about the challenges and opportunities in making cars ever more aerodynamic, which is a stated goal of Daimler - see
Mercedes to Sell Super-Aerodynamic Cars in 5 Years | Hypermiling, Fuel Economy, and EcoModding News - EcoModder.com .
Answers questions like:
Which components of cars do you believe have the greatest potential for aerodynamic improvement?
"The big action is at the rear," of course. (No news to EcoModders.) And he describes things the company is doing, and what it could potentially do. Plus chatter about wheels/wheel wells/underbody.
What do you think is the lowest drag coefficient possible for a mass production car?
Spoiler alert: Cd 0.20
He uses the GM Aero - Cd. 0.14 - as a starting point of an "impractical" aero car and lists several of its unacceptable aero features that would need to be compromised for reasons of safety/performance/practicality.
Not sure if he's referring to this car "GM Aero 2000"
Anyway, worth a read:
"A Drag Coefficient of 0.2 Represents the Sound Barrier" - ATZ online