Here's an update and some of the issues I've had since I made this post:

https://g35driver.com/forums/wheels-tires/159443-widest-tire-i-can-fit-my-03-coupe.html

I bought BFG G-force 255/40/18 front & 285/40/18 rear. I had them mounted on Ruff Racing model 279's: 18"x8.5" front & 18"x9.5" rear. Both front & rear wheels have an offset of 20.

The fronts are great, no problems at all. The rears on the other hand, DO RUB. No question about it. In my previous post I asked what was the widest tire I could fit on those Ruff wheels WITHOUT rubbing. I was told I'd have no problem with 285's on those wheels. I got news folks; 285's absolutely rub. Any type of mildly spirited turn causes a nice rub on over $500 worth of brand new rubber. I can't even imagine how much they will rub if I throw a couple passengers in the back. I'll probably look like John Force warming his slicks.

Other points:
The larger rear tires noticeably (to me) increased the rear ride height of the car. I can live with that. In addition, when looking directly down on the tire, the rear half of the tire is actually farther out than the fender. It appears there is plenty of clearance around calipers and various suspension components.

Questions:
1) Should I try a different offset for the rear wheels> Maybe a 30?
2) If I roll my fenders (which I'd rather not do), is there a chance they will still rub?
3) Do I have any choice about the extent of a fender roll? Also, does anyone know of a shop in Delaware that does this work? I'm in central DE.
4) Is wasabi good with a fender roll?
5) When the suspension compresses, does the top of the tire lean in? In other words is negative camber created when the wheel travels up? Old Vettes do that which naturally allows a fatter tire.
6) I appreciate any suggestions you may have.

UGH!

i have 285/30/20 in the rear and with the rear fenders rolled and have no rubbing at all...ive seen g's with as big as 305's, with stock non brembo rear brakes of course, in the rear so it is possible to even go wider...but it seems your not lowered at all but i recently got my rear camber kit put on which corrected my tires from leaning in and now they sit straight n i still dont have rubbing issues...so the best solution is get your fenders rolled

When you a bump, you should get negative camber. You should take it to a shop and see if it can be fixed by rolling the fenders. From the pics, it looks like it can be fixed.

that will clear easily with a fender roll and if you lower it. That's how my 20's looked when my car wasn't lowered. As I lowered it, the tires went right under the fender.

Its because of the BFG's, they are wider than most tires, and you don't have enough negative camber. You can either roll the fenders or swap to another tire size, or increase your negative camber a little bit

^ BFGs has a chunkyer sidewall.. you can try some toyos or falkens they'll probably fit if you roll the fender..

- Eric

wat everyone has said so far seems about right

roll your fenders. Is your suspension modded at at all? Looks like you have some toe in.

damn...thats a meaty sidewall

Do you have any pics? Before and afters?

I doubt seriously if I'm going to spend another $1000 on a different set of tires just to see if they work. If you look at my first post regarding this, plenty of people told me there would be no issues using a 285. They were wrong. So I guess there's no real science to this at all... just trial and error.

There are no suspension mods. Although, it appears I may have to some mods to get this right.

After doing some research, I've found that the same rear wheel is available in a 35 offset. No one thinks this is the best solution besides me? Looking at the fitment in person, I'd say pulling the wheel in by 15mm would make a big improvement. In addition, the BFG tire is so "meaty", I doubt it will appear tucked.

I'm going to say that it's your rear offset and rim width, not the tires. The rims stick out past the body.

I have the same BFG KDW's on 285/30/20 on 20x10.5 +29 and I don't rub. I rolled the fender for an extra margin, but I wasn't rubbing before that.

Rim offset has as much to do with rubbing as tire size. I think you would do better to bring the tire in with different offsets, but if you bring it in too much, you're going to rub the suspension on the inside. The OEM 19's are 19x8.5 +33 in the rear for comparison.

of course no one is going to be able to tell you down to the mm how much clearance you are going to have. The BFG's are likely the only 285 that is going to rub, any other brand will likely clear. Roll your fender and everything will be good, heck take it to an alignment shop and have them increase your camber by .2 degrees and it will likely clear.