[Joenavy85]

Originally Posted by aerohead

I've seen this argument through the years,and I believe it's based in urban myth or something.
A 'parachute' requires a 'clean',unobstructed flow source,which a rear bumper would not have available to it, unless a car was fully paneled,with laminar flow all the way underneath to the bumper,and the bumper extended below the elevation of the belly,into the laminar flow.
Without an operable diffuser,the leading,hollow face of the bumper would,simply be in train of a captured pool of turbulent air,traveling along with the vehicle.
I have seen some Ford cars whose rear bumper fascias 'quake' on the highway,but it's not do to 'parachuting,but rather due to the turbulent environment it's residing within.This should have been caught inside the aero-acoustic chamber.A true design oversight.Some webbing added to theinjection molds could have 'tuned' the natural frequency away from that turbulent signature,and any harmonic of it.

So the turbulence is similar to what you get in the bed of a pickup with the tailgate up, one big oval cushion of swirling air?