I am looking for some new tires for my stock 2003 xl7.  I do a lot of hunting, and am moving to Colorado in august and will need something with a little better traction. I saw in another post that a 225-70-r16 was the biggest I could fit without rubbing.  I found some better choices in a 235-70-r16.  How much would the bigger size rub?  

Keep the overall tire size under the 29" size (28.5" should be good) and you'll be a lot better off. I've got the 225/75 MT's on and they rub up front when turning. Rubbing only the plastic fender liner.

On the back, I've got a spacer so it's ill-relative.

To compare to max size, turn your XL7 front tire about half-way in the well. This should be the 'widest' the tire will get from the outer edge of the tire up front, and inner edge of the tire in back of the wheelwell. Take a tape measure and measure the amount of space there is between the tire and plastic well. Take the minimum from front or the rear. Add this to the current radius of your tire, subtract 1/2" and that's the maximum recommendation.

I have 325/70/16 tires on my GV.  I had to trim a good bit of plastic from the skirt under the front bumper (on the underside, where you won't see it).  The tires will rub slightly against the metal flange where the two pieces of sheet metal are welded to make the driver's foot well, otherwise it's been fine for on-road and mild off-road driving.

jSager