When Ford introduced air curtains on the Mustang in 2014, their
press release stated,
"It’s not visually obvious, but rotating wheels are a major source of aerodynamic drag. However, enclosing the wheels in skirts to smooth the flow just doesn’t look right, especially on a performance car like Mustang. Widmann and the aerodynamics team adopted a different approach for Mustang, giving it the first Ford application of wheel aero curtains.
Vertical slots in the outer edge of the front fascia channel air from the front of the car to openings in the wheel wells, directing it across the outer surface of the wheel and tire. The wall of high-speed air works much like a skirt to reduce drag while still leaving the beautifully designed alloy wheels fully exposed."
As the Preacher says, "All is vanity."