The legendary Yankee Tr-bar
 

I saw these installed on a 1960 Rambler, but apparently it's a tri-year Chevy thing?

https://www.jalopyjournal.com/forum/...-jpeg.3928924/
http://www.jalopyjournal.com/forum/a...-jpeg.3928924/

DDG/?q=tri-bar+yankee++outside+rear+view+mirror+with+ring&ia= web

What I see here is a converging duct. The 5" annular ring around a 4" mirror must create an aerospike. Compare to the 4" mirror as a bare flat plate. Needs testing.

I could replace my Superbeetle's front running lights with these as fender mirrors, remove the door mirror and put the turn signals in a Mexican bumper. It's either that or straighten out the one that's on it now.

They would look period correct !
Would certainly like to see them tested ' especially if the outer ring has some taper to it.

If it were a more-or-less straight cylinder with an annular wickerbill, or Gurney flap, just abaft the edge of the mirror (Coanda nozzle) it would pull air 'around the corner' and reduce the wake size.

Or not.