You would definitely stand a chance of rubbing, but you might clear OK. Those 275s are 10.8" wide as opposed to the 10" wide stockers. If you do experience any rubbing, you could throw a washer or two on your steering stops or go with wheel spacers.
Here is a good thread to read through.
Largest tire on stock JK? Here's your answer!
That being said, you would almost certainly be able to get 15", or even 16", wheels AND tires for cheaper than just the tires for those 18s. Those Trail Grapplers would total $1,485 (after $50 forum discount) for 5 from DTD, then you have to have them mounted and balanced somewhere. I have $1580 in my 16" wheels and 33" tires, mounted, balanced, shipped, locking lug nuts, and replacement certificates.