I'm running 19x8 @45p with a 235/35R19
18x8 @45p will be fine, 235/40R18 IMHO are a little big, 225/40R18 probably a bit better (I know the 235 would not be legal here, I don't know the laws in the State)
I'm running 19x8 @45p with a 235/35R19I decided against the +21 rims
Going the other way now I found rims from a GS450h
Anyone running 18x8 +45