I believe that they are to protect the rotor from splash. The rotor would protect the wheel from scum about as well as would the shield - but without the shield all that 'scum' hits the rotor. -glen I ripped 'em outta the way on both my '83 and my '87 GTIs and never had cause to complain. Never could tell if I got better brake cooling, and never seemed to collect scum in the wheels.