18 or 20 inch wheels

is it possible to get 18 or 20 inch wheels placed on the Pontiac G6 without any other major modifications? I dont mind axle adjustments but am I going to have to modify the body in any way? Or would 18 or 20 inch wheels just fit on the car without any other adjustments necessary? If there are any adjustments please let me know.

Thanks
-ryan

Not totally sure about the 20's, but the new 06's have an option for 18' rims. They are 225/50-18, At http://www.tirerack.com/ they seem to think 20's will work. Tell me if you go that big on yours. Takes some pics too. Have fun.