tEknoS13 wrote: ^ Agreed
Take an s13 for example, lots of them are rocking MB Battles 9.5" and 15 offset (lower offset) and if I'm not mistaken, s14 are capable of bigger wheels.
Well you have to be careful here, because the lower the offset is, the less rubber you can run under stock fenders.
To answer your question simply, OP, 18x9.5+20 should fit with ease. Maybe a little roll, depending on your tire size.
Next summer, I plan to upgrade to 18x10+20 all around with 255/40's up front and 275/40 out back.