I found this paper some time back on the aero / drag reduction of various wheel designs:
https://research.chalmers.se/publica...2_Fulltext.pdf
Looks like the basic flat cover isn't necessarily the best option.
The "thick outer radius cover" performs the best according to this research - probably why ABT use this sort of design on their formula e car and RS4: i posted about that wheel here but no one responded
https://ecomodder.com/forum/showthre...hts-37743.html
I'm thinking of trying out something like this on mine.