I have nice wheels left over that I used to have on my SL55 then my SL63.
Any idea if they will fit on a S550?
I don't know the exact sizes, just that they are 20" and the tires are like 275/35(maybe 45)/20 front and 305/25/20 rear.

Any idea guys?

I believe the offsets are not correct. You may want to ask the question in the tire/wheel forum- I'm sure it has been asked many times...

2009 Mercedes Benz SL-55:
Bolt Pattern (mm): 5x112
Offset Range (mm): 29 to 35
Wheel Size Range (in): 18x8.0 to 20x9.0
Front & Rear Center Bore (mm): 66.6
Stud_Size: 12x1.5

2009 Mercedes Benz S550
Bolt Pattern (mm): 5x112
Offset Range (mm): 25 to 42
Wheel Size Range (in): 18x8.0 to 22x9.0
Front & Rear Center Bore (mm): 66.6
Stud_Size: 12x1.5

I have 285/30/21 in the rear n 255/30/21 in the front and they fit just fine if that helps you.
I'm pretty sure the rear wheels will fit but the front might be too big. They might hit the side walls when u do hard turns.