This thread has kinda gotten off track, but I figured I would throw my experiences in the ring for posterity.

My 1995 C36 is lowered with H&Rs and has Blistein sport shocks. I run #2 pads up front and #3 in the rear

Original setup:
17x7.5 225/45/17
17x8.5 245/40/17 AMG Mono's (stock wheels etc)

No rubbing, no issues - as MB intended

Next wheels
225/40/18 & 245/40/18 Nitto 555 on 8.5x18 Brabus Mono IVs

The tires don't rub, unless the car is loaded and turning tight corners or on large bumps. The rears are perfect- nice ride, good wear etc. The fronts were a different story. The 225 is too narrow for a 8.5 rim. This stretched the tire and cause a number of issues:
1) Rounded side wall - looks like crap
2) weakens the tire at the point of contact with the road. This led to tread separation after 20k miles
3) Incresed wear on the inner edge of the tire

Next tires:
235/40/18 Yoko AVS DB2, same nittos on the rear

The tires looks much better. 235 is about as narrow as you can go on an 8.5 rim. But the fact that the width is correct and the tire is not stretched means that the tire is taller. Thus the car does rub on when the wheels are locked and you are turning.

What have we learned from this: 8 is the widest 18" rim you want on the front and 225 tires will fit it perfectly.

Not to start a flame war, but here is my 2 cents on the situation. 18's look great, but 17" rims are lighter, ride better, cost less and the tires are cheaper and last longer. To be honest most of us need to get over the vanity of running 18's and just head back to 17's it is what our cars were designed to run and what they run best on. If you show your car, the ignore me, 'cause you ain't gonna win shit on 17's. But if you drive you car, roll with 17's.

~dnm

Edit: thank god I don't get paid to spell....