You would need 1"+...oh yeah, you need 2+" lift too.
You will actually get more rubbing and have to do more trimming with the Spidertrax spacers.Tires will rub on the front mudflaps either way and the mudflaps will need to be removed or trimmed like I did.Relocate the inner fender liner forward if they rub there.Let me know if you want some pics.
I have a set of Spidertrax and tried them with my 305/65/17 MT KM2's ,which are about the same size as the 285's, I have now and with the 275/70/17's I had on.
No problem at all running stock rims with backspacing of 4.5 or 4.75 inches. Plenty of room. I can get my fingers between the tire and the UCA and I'm running real wide tires for my rim width and I have 4.5 back space on my Mojave's.What about on the UCA?