I have a 2021 g550 on the way to me. I plan on putting KO2’s on when it arrives. I’m trying to find out if the KO2’s will fit under the spare tire cover. I’ll be going with 275/55/r20 which is only 1 inch bigger in diameter and the same width at stock.
thanks in advance.

 

You MIGHT be able to adjust the cover that goes around the circumference enough to get the tire under the cover because the clasp is somewhat adjustable. I think what the issue will end up being is the cover plate (large round disc that covers the hole) will be too small at that point for the other cover to hold it in place. It's been awhile since I took the cover off, but I recall the fitment being pretty exact.

 

Maybe the '21 tire covers are larger, but the one on my '19 G550 wouldn't even close around the OE Pirelli 275/50R20 mounted tires, so MB slapped a Continental 265/50R20 on as a spare, and listed it on the build sheet as a "full size spare". Not sure what KO2 size you're installing, but I'm skeptical the cover will fit unless you wrap a cargo strap around it .
I'm not sure what you're supposed to do with the cover after changing a tire and bolting the larger one onto the carrier.