New to the bmw world

Hi guys, just got my first BMW E90 318d 2008 and love it already. Im just wondering if any one can help me out with tyre size as the back 2 dont match my front 2!

Front tyre size is 225/45/17

Rear tyre size is 255/40/17



Is this the correct sizing for the car or has someone messed around with it?



Thanks in advance & heres a pic of my car :)

New to the bmw world