Maui, I recommend staying with genuine MB wheels with the same offset (ET Number stamped on the back of the stock wheels) instead of any aftermarket types since MB wheels are hub-centered. Even with genuine MB wheels be sure that the lug bolts have the same thread engagement in the hubs to prevent causing problems with the parking brake mechanism ... simply place a lug bolt in a lug bolt hole of a loose wheel and see how much of the lug bolt protrudes beyond the back of the wheel. You can check the Tire Rack website for info on the circumference of different tire sizes (shown as Revolutions per Mile). Keep in mind that switching to a tire with a different number of Revolutions per Mile than the original tire size will affect the speedometer accuracy. As already mentioned larger wheels may adversely affect the handling characteristics of your 1991 300E ... the MB engineers designed the suspension with 15" wheels.

__________________
Fred Hoelzle