I read in the "book" that the spolier reduces the cd from .32 to .31. I've avoided getting it as well as the Appearance Pkg. for reasons of weight as well as the possibility that the spoiler will cut down rear vision. It's been MHO that the aero stuff really doesn't do much good except for possibily the front air dam and the rear spolier at speeds not normally driven, e.g., in excess of 100mph. What I'd really like to know is if anyone knows whether either the spoiler or air dam increase down force. In the past, one or two of the really fast cars I've had seem to get light at the rear when I've had occasion to exceed 110-120 mph.