I THINK the largest you can run according to 'the books' is 270 but I'm not sure how much you can push before having problems. If you wana guess it measure the diameter of the wheel well and thats a start. Then I'd go underneath and measure the travel of the suspension and you'll be able to figure out the max physical tire size through that.
You need enough clearance overhead for the it to bottom out which is the travel, add an inch maybe for safety, then measure from there to the ground. If that measurement is bigger than the wheel well then the wheel well restricts it and you can't go bigger than the wheel well. Also try and figure out how it'll work with turning the wheels.
Will need to try to visualize it in your head.
Just math.