Originally Posted by OKC-XFR

Very true for a coupe - but a roadster with the top down has a much different shape. Also, it seems that the windshield with the open cockpit would disturb the airflow sufficiently (in the manner that the spoiler does) to reduce lift - I've even got a wind diffuser, so the airflow over the top of my car has to be a real mess...I think you need laminar airflow to create lift, but I'm not an aeronautical engineer.

I'm curious because I remember that +fireamx did a test and found that his highway gas mileage improved with the wing down by over 2 mpg - I would be tickled to get over 30 mpg with my car!