35mm with 8 will work but with 8.5 you might be hitting fender lip quite a bit. 45 on 9.5 will be fine for the rear though.
Thanks! I was wanting to run 255/35 F and 285/35 R but if I have to stick the 235's up front, that shouldn't be a problem. My rear lips are rolled already for the 315's on it now so I am not worried about the rear tire size too much....kflee said:18X8.5 with 35mm offset will work fine on the front with a 235/40/18 tire. A 255/35/18 with the same wheel will rub under hard cornering.
The rear size you listed will work fine with a 275/35/18 tire.
BTW, I have run this same size on the front of my car with no problems and ran at an autocross and a road course.