I'm not sure how else to explain this....the basic W204 chassis was designed to accept 225/45-17 tires at all four positions. With this capability, the planners created a Luxury model. To make the Sport model seem sportier (and it makes little to no real world difference) they put slightly wider tires on the back. There is NO REASON AT ALL why you cannot put the same 225/45-17 on all four positions, just like the Luxury model. I do this every winter when I use winter tires all the same size. I don't know if the wider tires will fit up front, as I have not tried and there is no reason to do so. You need a different tire store.