I have 285/70/17's on OEM Rubi wheels on the stock carrier- it touches the CHMSL bracket, and the rubber bumpers, but no problems with it. A spacer is in the future, however, as I'm anal when it comes to such things Mark W.
They can support the weight just fine- it's tire width that becomes an issue. Having the lugs hold the spare on allows for plenty of strength. You simply can't fit wider tires on there without spacers, or an issue - Mark W.