I've got 225/50/16 on et11 wheels (same wheels as the ones in post 17) on a 1973 450sl. There is at least a half inch of clearance (room to grow) on the outside of the rear tires on my car. This is really good/interesting information about the bulging sidewalls on a 55 profile tire. All the calculations I've seen (like those on rimsntires.com) do not show any sidewall bulge growth with increased profile size. They seem to basically assume that a 225/55 tire will be no wider than a 225/50 tire, assuming only the diameter would change.

Since the 225/50/16 tires I have on the front of my car rub on the outer front edge when turning and braking in reverse, I would expect you'd have even bigger problems with a 225/55/16 on the front. The small gap you see in this picture (of 225/50/16 tires) closes when hitting the brakes in reverse. http://www.benzworld.org/forums/attachments/r-c107-sl-slc-class/306402d1273018411-pentas-nobmobile-pentas-004.jpg

Here's a little bit of an effort to show the max tire sizes that you can fit on the front of an r/c107: http://www.benzworld.org/forums/r-c107-sl-slc-class/1595455-how-much-tire-can-you-stuff.html
... and the rears: http://www.benzworld.org/forums/r-c107-sl-slc-class/1595451-how-much-tire-can-you-stuff.html

Based on the way the calculations were being done in those threads, I'd assume you'd be fine with 225/55/16 on the rears. So this thread may have just taught me something new. Thank you!