well u dont have to but more than likely the brake dust in there will cover them over quickly so u may want to primer them sand down the primer till smooth and then paint and seal with some clear coat that can stand the temperature down there cuz i just painted mine and the were nice and blackish in about a month, but then again i dont really care about it so i just painted over the crud again, if they were smooth i'm sure they wouldnt hold so much crap