my mates all run 18x10s as drift rims and lnever had a problem running a 235 40 R18 on them, i have 235's on my 9s atm and looks ok but not much strech +22 offset looks good i run neg 2 on the front and .5 on the rear for good tyre wear and they clear after 10mins with a rubber mallet....
one of the guys put a 215 40 R18 on his 10s and that was a bit extreme...... looked to streached