In the rear, it's a 9" wide wheel, so you can get a pretty big tire on there. 295 for sure (I've seen a 295/30R19 Hoosier A6)...I suspect you could wedge something even a little bigger on there.

In the front, it's a 7.5" rim. I think 245 is pretty much the practical limit...I've had both Hoosier A6 and Kumho V710 245/35R18 on my car for autocross...you're going to have trouble mounting anything wider on the wheel, plus there's a ball joint stud that protrudes into the vicinity of the shoulder of the tire that you need to be careful of. I normally use a 5mm spacer with those wide fronts...wider track to combat the push and gives a touch more clearance at the inside shoulder.