ACID64

So I've finally got my Cutlass driving, and now it needs a set of wheels. I'm pretty set on 18" for both front and back. I'd like to get some 18X9 in the back and 18x8 up front. I'm planning on dropping the car down a couple inches for a nice pro-touring look. So my question is what is the widest tire that will fit up front on 18x8" without serious rub? I found this site below and looks like 18x8" would work with 245/40/18 anyone have experience with this? I'd like the tire to be wider than the rim to protect the rim a little.

http://www.chevyasylum.com/tech/backspace.html