I think mine are 205/55/16. Just make sure your offset is ok; i had 36mm offset rims at one point so i had to switch back to my old ones until i could find 22mm offset ones. 23 is the number given by mercedes techs, but i think 22-25 maybe 26 will be fine. Otherwise the install is pretty easy.
One more thing; DONT use spacers - i ahve heard nothing but bad things about them, especially at highway speeds.