Somebody needs to clue this old guy what "concave" refers to when we're talking about wheels. All I know is what it takes to fit (or mostly fit) wide wheels. Beyond that, I haven't ever tried to describe the wheels.
Anyhoo, I do have an update . . .
Previous 3-season, autocross, and track day setup: 255/45-18 Goodyear Asymmetrics on 18 x 9.5 x ET+45 SVT/GT500 wheels.
New track day setup: 285/35-18 Michelin Pilot Super Sports on 18 x 11 Forgestar wheels (front and rear). The tread is entirely under the sheetmetal, but there isn't even 1mm of offset to spare on the strut side to tuck them in any further (I ended up making an 0.025" thick spacer - that's 1/40
inch, not a mis-type - to eliminate a rub).