How wide a tire can you put on the stock rear?

I'm a firm believer that wider tires on the rears can translate to some awsome 0-60 times for this car. Much like the Mustang Saleen this car suffers from very poor launch control as there is just way too much power/spin at the get-go.
Does anyone know if you can put 275 or 285 width tires on the stock 18's?