It's all about your personal risk tolerance I think. Riff will swoop in and tell you that you'll be just fine, and there are certainly enough members here that run 285's on their stock 7" rims with no problem, but you are correct in that the manufacturers don't recommend it. Personally I wouldn't do it, but then again I have an infant and a 2 year old in the VX all the time now (Axiom engine is having an issue) so I don't want the risk of a separation at speed.