The fender lip is necessary for aerodynamic reasons. When we install wider wheels and tires, even though they fit (I had 9" and 265mm tires in the RS), they create an aerodynamic wall, and they promote lift. The fender covers the top of the wider tire, but the bottom is largely exposed away from the bodywork, increasing both drag (bad) and lift at speed (very bad). It is necessary not to have the tires exposed away from the bodywork.