If they are 18x9 all the way around, they came from Saleen with 255-35-18 fronts and 265-35-18 rears, usually Pirelli's. The upgrade option was for 10 inch rears in which case they used 265-35-18 fronts and 295-35-18 rears.
99-122 Bright Atlantic Blue S281 S/C Convertible
11-025 Grabber Blue S302 Convertible
Saleen - Power in the hands of a fool!