Subject: What devices help race cars take turns at faster speeds? And how?

I've seen spoilers on the back of race cars and skirts on the bottom and I 
wonder what these accomplish for the car on a banked track.  I understand 
that friction between tires and road creates traction and I understand 
some of the physics of taking turns, that a component of the normal force 
is directed horizontally toward the center of the curve and thereby allows 
for higher speed than on a flat road (when FNsintheta=m*v^2/r no friction 
is needed to keep from skidding) but I don't understand the physics behind 
using spoilers and channeling air beneath the car to take the turns faster.

Re: What devices help race cars take turns at faster speeds? And how?