So I had heard that the brakes were bigger on the front of the new G550, but it seemed so slight.
I found from a friend that the dealer he works for has a G550 in, so I went down to check it out.
It was being prepped in the back, so I brought along a 16" wheel (spare from my G500). Indeed it will go only on the rear of the truck. Just FYI, confirmed, you would need to retro back the brake rotors and calipers to G500 in order to fit the smaller wheels on the 2009 and newer gklasse