A lot of people will spray their car with some sort of traffic film remover when washing it. They might even spray a product on their wheels, like wheel acid for example, which is a weak form of acid, which helps take the dirt off the wheels. In theory, you can just jet wash it and it cleans instantly which is brilliant, but the big issue is that the carbon ceramic discs absorb these chemicals and accelerate the rusting process.
Here is an example of a brake disc, as you can see on the back of it, I’ve identified where two of the screw heads that hold it to the hub have come off completely. This is a known fault with Ceramic Discs.
This is of course, a safety issue and must be dealt with by means of replacement discs. Have a look at the photograph of the brake pad, you can see quite clearly this is a result of chemical damage because the chemicals have only made contact with the outer part of the pad, not the inner part. You can see the shiny part of the pad is where it has contact to the disc.
The outer part of the brake pad, which should be black with a nice finish, instead the surface has been eaten away and left a rough and deteriorated finish. This will also cut away at the discs smooth surface. So the official advice is that if you’re washing your car, don’t put anything on your wheels or brakes other than water. No soap, suds, etc. It should just be warm water to clean the wheels.
The chemicals change the colour of the hub. So the hub at the front should be black, this one’s grey, and from the outside, it might look okay, but they rust on the inside very bad indeed.
If you use a local car wash please insist on no chemicals.