Originally Posted by Kurts
Bad idea......your car is shaped just like the wing of an aircraft & will generate lift - even more the faster you travel.
In other words, the tires of your car begin to literally lift off of the ground and the loss of traction will make your car unstable. Think of it as driving over ice: no traction means no control. Anytime your tires aren't contacting pavement you're toast.
Spoiler up=good thing!
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!