I'm running 275-35-18" on the rear of my SEC, but haven't lowered the car yet. I have been told that they will most likely rub, if the inner fender lips aren't rolled before lowering. They sit on 10" rims.
My father-in-law runs 285/35/18 rears on his SEC with 23 offset 9.5 wide wheels and only experiences minor rubbing on hard cornering. He has the H&R setup on his '88 560SEC. Every car is a little different it seems but you should be safe. The offset on my rear 17x10's is 17 and I didn't have to roll fenders with the 275 tires.
BenzWorld.org forum is one of the largest Mercedes-Benz owner websites offering the most comprehensive collection of Mercedes-Benz information anywhere in the world. The site includes MB Forums, News, Galleries, Publications, Classifieds, Events and much more!