Lowest production car I can remember is the GM Impact at 0.21, from memory. 0.28 was the target for a long time for fuel efficient cars, but the reality is it doesn't make the car especially efficient in the tests or at legal speeds.
Aero is not a zero cost attribute of the car, and a low CD can force a deterioration in lift characteristics and crosswind stability.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376
It's easier to get low Cd with high A. Modern cars are bigger so Cd does drop. One thing that made a step change was realising that the flow through the engine bay was significant and you could get 6% typically by tidying that up. Some aerodynamicists run their cars in the windtunnel with the grill blanked off, a detail that gets lost in the marketing spiel. Also there are very substantial differences in results between different tunnels, and even differences when different manufacturers use the same tunnel, due to the test procedures used.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376
I used to have an 87 Benz 190D 2.5 and that had a radiator shroud with thermally actuated louvers and aerodynamic covers under the body. I see that listed as Cd .32-.34, that (the W201 body) and the W124 and W126 bodies were when MB got serious about aerodynamics I think.