If you are getting 18s, I wouldn't go any lower than a +45 offset. I have 18s with a +42 offset, I don't rub, but I'm also only lowered 1.25 inches. You don't seem to have that aggressive of a drop, so you should be fine with the proper offset wheels. I wouldn't go any higher than a 7.5 inch width, with no less than a +45 offset on your application.