Your first post was, "Will a 255/55/18 rim and tyre fit without rubbing with 30mm lowering on a T6??"
Your second post was, "I’m currently running on 255/55/18. Are the 235’s giving a possible more clearance on full lock I take it ??"
Your third post was, "Forgot to mention I’m also lowered 30mm"
So the best person to answer your first question is......you.