first off, air dam- vertical aerodynamic fairing in the form of a skirt (for the purposes of this thread) or flap for the purpose of forcing air below protrusions as to lower aerodynamic drag.
spoiler/splitter, creates downforce, and/or splits the air in a deliberate way to control lift otherwise caused by the body of the car and aerodynamic forces.
I digress
So, I went back to the chevy dealership today, and gathered some data for consideration/discussion.
I use the cruze/volt because they are the successor to my car, the same size, and look like they are pretty close to the same in relationships to dimensions important to this project.
For the data... well, my phone deleted it, so let's go from memory. figures are pretty close.
the malibu, impala, and cruze were all around 7-7.5" for ride height (measured behind the front wheel), the volt was about 5.75". the malibu and cruze were the only two with stepped air dams, so I think this is styling/practicality, not aerodynamics. all the air dams except the volt's had stuff hanging down slightly below them, and height from the ground varied (despite the constant ride height), so this seemed to be dictated by the lowest hanging object* erring on the side of clearance slightly over efficiency.
my car sits at 9 inches ride height with 9.5 at the front bumper cover.
*the lowest hanging object argument. the volt varied here, it had an air dam that went from 3.75 to 4 inches from the ground in the center, so I got to looking at the cars, and noticed something, then I looked at the camaro and it shared this characteristic. the thing these two cars shared that the others didn't (didn't look at cadillacs, here, as they are more about performance than economy, try squeezing 45mpg from a twin turbocharged ~450HP v6) is not only did nothing hang down below the air dam, but they had a chine/splitter (what exactly it is could be debated, but that's not the point) allow me to explain. the attached picture shows a cross section of the bumpers with the deflector. the deflector is about the same distance from the front of the car, but on the volt and camaro, there is a jut out to split the air just above the lower air dam. this increases cooling (camaro) and lessens how much air hits the air dam, possibly limiting the increase in drag experienced by users on this forum, if not eliminating it. this splitter/spoiler goes the full width of the radiator opening then tapers off.
front tire spats, they all had them except the volt, and forgot to look at the camaro, but they were between 1.5 (cruze) and 2.5 (impala) inches tall. they all met with the air dam, likely to eliminate air spillage mentioned in the stickied first gen prius thread. these will likely be integrated into my air dam.