30x9.5 on 15x8 rims
I have 30x9.5 AT radials mounted on 15x8 alloy rims on my 2001 TJ.
A 30" tire is 2" taller than the stock 28" and gives me one inexpensive inch of additional ground clearance without the expense of a lift. The 30" is the tallest tire you can run without a lift which does not rub at full articulation or in a tight turn.
As your tires get taller, you raise the center of gravity, lower your mpg and complicate your steering geometry. Taller tires also lead to re-gearing, the need for stronger axles, heavier spare tire rack and slower acceleration.
With 31" tires, I'd gain only 0.5" more ground clearance over the 30" and I'd need a 2" lift.
If I go up to 32" tires, I'd gain 1.0" more ground clearance over a 30" tire and I'd need a 3" lift.
The 15x8 rims allow the sidewalls of my 30" tires to run more vertical without bulging and lets the top to the tires run flatter for better wear and a good footprint.
For my application which is go-long, mild off-road adventure touring, I believe my set up gives me the lowest GOG, best mpg and most ground clearance without unwanted additional expenses.
That said, if you have the money, like the look or have the need...GO BIG.
John