et40 is probably the furthest I'd want to run on my own car being lowered and all (BC Coils). I push my car in autocross and backroads so fitment is very important to me. I've had 17x8 et 40 and I would rub on large compression's. I can only imagine how bad I would rub on an et30. I would return them and get the correct offset
edit: I'm not
that low, on my 17x8 et40 setup I had a 2ish finger gap and I occasionally rubbed on the street. At autocross I managed to rub through my
fender liner on 215/40/17 Federal RS-R's