RE: How will aerodynamic testing change the Challenger design?
"Lift" is caused by air traveling faster above an (elevated) object than below it. The reduced pressure above the object (from the air passing over it faster) causes lift.
NASCAR addressed this issue (cars becoming air-borne during wrecks) by installing roof flaps on the cars. The flaps open naturally (again, from lift - air passing over the flaps faster than going through the cab / under them) when the car's "attitude" is disturbed and it equalizes the pressure that would have precipitated the car going air-borne without them.
"Downforce" is the opposite effect - air passing under the car faster than over it - and in exotics, is usually achieved by smoothing the undercarriage with a "pan" to induce faster/smoother air flow, and disturbing the air above the car with angular facets that use the air to force the car down toward the pavement. The air actually "sucks" the car toward the pavement. (An F1 car has enough downforce to keep it glued to the TOP of a tunnel at 230mph. That's pretty amazing - and helps explain why their fuel consumption is so high.)
While downforce is a positive - especially at high speeds, anything that disturbs the "slipstream" and creates downforce also creates "drag". Drag and friction are the enemy of fuel efficiency and maximum speed.
The key is to balance downforce with aero-efficiency. While some drag/downforce is necessary to maintain stability, too much makes the engine work harder and wastes fuel.
I think with the current and upcoming CAFE standards - required by law, automakers are trying to achieve a balance between styling, fuel efficiency and handling while maintaining as much power as possible. They seem to be trying to direct air "around the cars" more than over or under them now.
Do you remember the cars of the late 1970's and 1980's? They all looked like the same "wedge of cheese" with different nose and tail treatments. No one wanted the cars to look like that, but the engineering was lacking to make adjustments for fuel efficiency to the drivetrains and meet the standards that way. So the effort was concentrated in aerodynamics. Everyone got sick of seeing the same cars on every lot, and the cars that "stood out - styling-wise" started selling faster than the econo-boxes. So the automakers adjusted and tried to give everyone the best of both worlds.
I'd personally sacrifice 1 - 2 mpg to have a great looking/styled car instead of having a generic econobox that I can't find in a parking lot amongst all of the others.
Oh well - just my two cents.