To fit 20's sucessfuly, you will need to remove the plastics in the wheel wells and probably trim the Fenders
to fit them, not just roll them; Material will have to be removed from the Fenders
, and the sharp edges will need to be rolled. You will also need to add Fender
flares, you could do it, but it would take some tweaking.
Needless to say, your speedometer wouldn't be accurate anymore after the swap, and the sidewalls on the tires would need to be so short that You'll be sweating bullets just thinking about potholes.
Personally, I wouldn't go bigger than 17's, anything over 17's is generally considered overkill on our cars.