[USMCGunrock]

Are you talking about the "No Trim", "Little Trim" & "Moderate Trim"?

If so, the "Trim" means trimming your wheel wells to fit the larger tires because if you don't your bigger tires will rub. So if, lets say, now that you have a 2" lift and you want to get a bigger size 265/70/16 (about 30.6" compared to stock 29.5"), you will have to "Little Trim" the front bumper because that will rub a bit when you flex or turn your wheels.

 

[USMCGunrock]

You want it to stick out more, now you are looking into back spacing. The less the back spacing measures, the more it will stick out. I'm still new to the WJ but I think if you are going aftermarket wheels, 4.5" backspacing is what people get...someone can chime in on this and correct me if I'm wrong. You can also get wheel spacers to use with the stock wheels usually 1.25"- 1.5" will do.

But yes, 245/75/16 will be your max size without trimming.

 

[USMCGunrock]

I used these spacers on my XJ...no problems whatsoever. Torqued right and checked every tire rotations. I had Canyon OEM wheels with 32" tires.
http://www.roughcountry.com/wheel-spacers-1091.html