Kat (Sue), with the tires that you are describing you should only have to trim the point off of the front cladding which is a MUCH smaller piece from what is shown in the picture Dub posted.
If you stand next to the front tire (let's use the drivers side as an example) and look right in front of the tire you will see that the cladding comes to a point. This point is at the very bottom of the cladding at the front of the wheel well. The only thing you really need to do with the 285/60/18's is knock that point off. I turned my wheels until they hit that point to give me a reference on where to start cutting. I HATE to maul my baby so I cut very little off to begin with and then kept sanding and sanding until I had just cleared the tire.
If you went with the Nitto Terra Grapplers that should be all you need to trim. I was stock height with the TG's for my first three Moab's and never had a rubbing problem. Moncha had the TG's and was stock height this year and I don't believe that he had any problems either.
You're going to LOVE your new tires.
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