What is going to keep the car on the ground at speed and/or a strong side wind?
An aerodynamic shape with negative lift.
Little known fact: when aircraft models are tested in wind tunnels, they are tested "upside down" so that lift forces are added to the weight of the model. The model is "pushed" down instead of up.
For another example of a shape which is pushed down in a wind, look at one of the genuine Mexican Sombreros. The real big ones with a turned-up lip around the outside. Despite the American perception that it is just a goofy-looking hat, it is an areodynamic surface which causes a wind to force the hat tighter onto the wearer's head instead of lifting it off and blowing it away.