These are the wheel and tire sizes Chevy released today for the E-Ray.

Brake Rotor Size (in. / mm):Front: 15.7 x 1.5 / 398 x 38
Rear: 15.4 x 1.3 / 391 x 34
Wheel Size:Front: 20-inch x 10-inch (w/5 x 120mm bolt pattern)
Rear: 21-inch x 13-inch (w/5 x 120mm bolt pattern)
Tire Size:Front: 275/30ZR20
Rear: 345/25ZR21