Sill Covers and Side Airdams

     These devices have been installed on cars since the end of the 1970s，the main purposebeing to protect the lower body side (rocker panels and doors) from corrosion caused byabrasion due to stones，salt and mud projected from the wheels. At that time，body sheetswere never zinc-coated and therefore abrasion of paint layers could expose steel sheets torapid rusting and deterioration，mostly in countries affected by icy winter climate andwidespread salt spraying on roads to contrast icing.

    Other advantages of sill covers include the opportunity to model more freely the lowerbody side，usually conditioned by the forming process of the upper side and by its size，improved protection of door opening from dust，mud and powder, and possible influenceon vehicle aerodynamic properties. Nevertheless sill covers are additional components inany case, therefore increasing costs，investments and weight (from 2 to 4 kg per car)．

    In recent years，widespread use of zinc-coated steel，under floor PVC spraying duringthe paint cycle and polyurethane transparent film application on the painted body, hascaused sill cover advantages and their adoption to be reduced especially on smaller,economy class cars.