Those are great looking wheels and would look nice on a Crossfire. I have the same size wheels on my car. for the extra width I am runing 235 40 on the front and 265 40 on the rear. I may change to 275 40 in the near future. A big advantage to these size wheels is you have a much larger selection of tires in every price range to chose from. I also believe the ride is improved in the rear with 18" wheels. With any MB wheels you will need spacers in the rear. As long as you use hub centric spacers and the correct length lug bolts there is nothing to be concerned with.