If you drop it say 2inches, 17's will be more than enough. 18's are a bit overkill in my opinion. You lower to remove the gap which is what causes your wheels to seem small. If you have a FWD, you will want some tire on that rim otherwise your tires will break loose that much easier.
Peronally I like running 16inch rims with a slightly oversized tire. This allows you to have a little bigger overall sized wheel and it keeps the performance aspect in check. The more tire, the better traction ( for a 1/4 at least).
My buddy has my old car. I'll check the tire specs next time I see him. The tire sticks out over the rim a little bit. The car has massive traction out of the hole. It's ridiculous
