Many thanks for finding/posting this.
It is interesting to note that the maximum drag reduction, 8.4% resulted from running an open rim front wheel and a closed rim rear:
It is notable that in the previous tests of different underbody air dams the front
rim had been closed!!!
Can it be that "open rim" means the rim types that come OEM?
I wonder , to what extent would rear wheel skirts stand in for the "closed rim?"
I take it that a closed rim is essentially an aero wheel cover.