255's should fit depending on the offset of the wheels.
Currently i'm running 18x8.5 ET30 all around and have a nice flush fitment with a little room to spare for 245's or 255's up front. (currently using 235/45/18's, that size was on super duper liquidation, bought these tires to tear them up
)
If you are looking to stay with 18's, I might sell my set of lightweight TRMotorsports C4's (aprox 20-21lbs per wheel).