Look at
THIS
It's an air ride system by a company called praxis, it does lower the car and improve stiffness as it goes down in pressure. This article really puts into sharp focus what is going on with that lower piston as the pressure is let out of the bag and it rolls down over it, increasing the spring rate, despite the lower volume of air in the bag itself. it comes with a nifty 3 position switch that goes from normal, sport, and track.
But to put it as short and sweet as possible for airride's stuff, the difference in pressure to go from "normal" to "extremely stiff" is a matter of less than a half inch on most properly set up bagged pro-touring cars. and "normal" to "cushy" even less the other way.
The mind automatically pictures this 4x4 looking car hanging corners, but that's not what happens at all.
Here's another article on praxis' BMW system. Why isn't the pro-touring air ride guys offering something similar?