245/40/18 Stock Susp. Will I rub?
 

Anyone know? Will I have to roll my rear fenders?

Depends on the offset. With 45mm you should barely clear with slight chance of rubbing the springs with the wheels turned, if you did not add any negative camber. 40mm with 2.6* of camber will rub slightly, from my experience.

I ran(on pothole infested LA streets) 255 40 offset 18s for a week before installing my kw no rubbing...

THIS
Especially in the front.

The rears will clear with no problem.

In the front offset is just about everything with this tire widths 245+ in size, especially on 9" wheels. You're shooting for 45-35 offset with 9" wide wheels on 245-255. Make sure to have a pair 3mm hubcentric spacers handy just in case you rub due to the difference in tire width from one mfg to another. Once again this is specifically in the front. The rears will clear no problem.

Why not go 245/35/18? Rolling diameter remains the same as stock and absolutely no rubbing