The 17s are pretty limited as far as tire selection, and without spacers we are pretty limited on width as well.
If you want to add a little meat, the 235/80/17 is about 1 to 1.5 inches taller (depending on brand) and still narrow enough that the rears wont touch even under heavy load.
Anything more than 235 will probably need a spacer to keep the tires from touching under load/ towing.