I hear tihs a lot because the RS5 is more broad, rather than bulgy.
When you look at RS5 on 20" wheels, it eats them up and looks great.
When you look at a new S5 on 20" RS5 wheels, you IMMEDIATELY know you’re looking at an S5…it looks so mild in comparison. You instantly know that they don’t belong on the car.
Interesting.
http://www.tagmotorsports.com/gallery/Audi/__2013%20S5%20on%20RS5%20wheels-3.jpg
http://www.tagmotorsports.com/gallery/Audi/__2013%20S5%20on%20RS5%20wheels-2.jpg