A few questions, interpretations of windtunnel data

[Dane]

Something that caught my interest was the 240Z Silver Car (#19). When ZG Flares were added to the car (#20), the CD decreased from 0.454 to 0.433, the frontal lift decreased from 207 lbs to 127 lbs, and the rear lift decreased from 81 lbs to -32 lbs.

 

From my understanding...and please correct me if I'm wrong...the reason the flares reduce drag is that they "shroud" the top edge of the tire, which cuts through the wind at twice the speed of the car (not in the windtunnel since the wheels are stationary). Since the top edge of the wheel cuts through the wind at twice the velocity of the car, it contributes significantly to the car's drag, so covering it with the flares significantly improves the cars aerodynamics. I also noticed that the tires on this car are very wide, so that they stick out more than stock. With that in mind...would the ZG Flares have the same drag reduction benefits on a car with stock width tires?

 

Another question...on #28, 90% of the front grill opening was covered and the fender vents were opened. CD was reduced to 0.404, frontal lift was -154 lbs and rear lift was 45 lbs. It was hard to tell from the videos, did this car use a front air dam as well? Most pictures I have seen of race cars with covered grill openings also used air dams...so I'm wondering if it is worthwhile to cover the grill without using an air dam as well? I know that the air dam is designed to prevent air from getting under the car, but with the fender vents there to allow engine compartment air to escape...would it be worthwile to cover the grill opening without an air dam?

 

One more thing...I noticed from video #22 of this car that the strings on the rear hatch window clung to the car, indicating a lack of turbulence (laminar flow?). From my reading of Z aerodynamics in the past, the airflow separates over the rear hatch. Was this change due to the vortex generators on the roof?