Rusty disc faces - probably because you lot never let a jet wash get near your car. The calipers/discs/pads can collect brake dust, which has microscopic metallic particles in it - hence a large metallic surface area. This large metallic surface area then "faciltiates" the rapid rust build up - obviously being most evident on otherwise shiny disc faces, but also forming on the actual brake pads too. Take a close look at the edges of the pads if you doubt me. Give your discs and calipers a thorough rinse with a jet wash (obviously being sensible about not being too close), and the rusty discs should be reduced. Also, next time you remove your wheels, put a thin smear of anti-seize paste on the mounting face, and the centering hub of the wheel mount, and a smear on the wheel bolt threads and conical face - and this will massively prevent galvanic corrosion.
