Here in making sure you don't rub. I am very close on my 17 275 as well. But I know alot of people that run 285s but mostly on 18x10s. Hmm a 285 is only 10mm wider than 275 and 10/25.4 or approx 2/5 of inch wider overall or 1/5 on each side. If you think you have about another 1/5" of spacing between your wheel well and your tire then I would say you are ok to bump to a 285. However I have seen a 285/40R17 and I think its sidewall is too tall. so I wouldn't do for just that reason :-)