285/30's would be great, but how doable is that on a 8.5" wide rim with a +35 offset?
275/30 seems like my limit.
285 wide tire on an 8.5 inch wide rim is ridiculous and is definitely outside the recommended guidelines for a tire fitment of that size.
As you say, 275 30 20 tire is the limit on that 8.5 rim but you will get quite a big tyre bulge.
What you are doing is putting a 275 mm wide tyre (tread width) on a 216 mm wide wheel (ie. an 11 inch tyre tread on a 8.5 inch rim). Yes it is going to look pretty stupid (or ugly as you described it).
With a 275 tyre on those 8.5 wheels with the 35 offset you are definitely going to have the tires fouling the rear guards with sufficient suspension travel (and probably the rear bumper bracket as well. ).
You are going to have to roll the rear guard lips to fit the tires as they are going to protrude just over a half inch(approx 0.6 inches - 15 mm) further out than the 245 tires now fitted on the 35 offset 8.5 rims - and you will find you don't have that much clearance now between the face of the tire wall and the inside of the rear guard lip.
I would suggest you measure it all up carfully before you decide what you want to do.
If it were my car I would be looking at doing a 255-35 20 tire upgrade on all 4 wheels rather than trying to run 275 30 20 rear tires on a low offset 8.5 inch rim.
