Believe it or not, I'm running a 35x12.5-15 on a 15x8 aluminum wheel on the stock tire carrier. I had to re-weld and reinforce the OE tire carrier (supports and whatnot) and it holds it.
The door does close, requiring a bit of a slam. I worry mostly about the hinges... Supporting that kinda weight isn't good at all. When the door is closed, the hinges don't seem to br suffering much, but the open and closing takes it's toll. The bolts holding that OE carrier to the tailgate that worries me... But it still looks fine.