this maybe of help to you ......ref tyres think you should be safe going 235/40/18 front and 255/40/18 rear.its pretty much what i run.
wheels are 9.5j with 20et running slight spacering = 2et fronts and 10.5j with 20et running slight spacering = 2et rear.....have run 0 offset but fowled on turning....zed sits low on tien coilovers rear arches rolled and fronts have pull.