There's probably some data in the seminars.
The 1938 Adler-Jaray was tested for skirts:
* no mods = Cd 0.38
* front skirts only = 0.37
*rear skirts only = 0.34
*front and rear = 0.33
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At MIRA,the Audi A2 was tested with rear skirts.showed a delta-0.001 drag reduction ( on a car with normal Cd 0.288)
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Hucho says that the better the flow leading up to the rear skirts,the more effective they become.No truly-low-drag cars are without them.
Wheelhouse volume is going to affect them.
Underfloor condition will affect them.
Presence of 'taco' fairings will affect them.
Ditto actual wheel fairings.
Or combination of any and all.
Very conditional !
