245/40-18 is not a good size tire for the 9th gen Civic, or any other generation Civic for that matter. S2KJay is on 225/40-18 I'm pretty sure and I'd say that's a tad too big for our cars, but he's stretching them over 9.5" wheels, so that probably takes care of a couple hundredths of an inch in overall diameter. 235/40-18 on 8.5" wide wheels is going to be too big. Of course, this is all assuming you'd like the car to function properly. If you're just going for a certain look, I can totally understand. I had 15x8 +10r +25f Equip 03s with 195/45s on an EJ1 before, so I understand not giving a **** about maintaining close proximity to stock tire size, but I just figured I'd let everyone know that 245/40-18 is entirely too big for a Civic.