- Some cars use the same disk brake pads for the foot brake and the
- Some cars have have disk pads for the foot brake and separate smaller pads on the same disk surface for the parking brake.
- Some cars have disk pads for the foot brake and separate shoes on a different surface of the disk that act like a drum brake for the parking brake.
- Some cars have a single drum brake with a single pair of shoes that
functions both the foot brake and parking brake.
For 1 and 4 above, it is obvious that the single set of pads or shoes will wear as the foot brake is used.
For 2 and 3 above, under normal operation, the foot brake pads should wear out and the parking brake pads/shoes shouldn't get any wear, since they are only in contact with the disk when stationary.
Wear can occur on the parking brake friction material if the vehicle is driven by mistake with the parking brake engaged partially or fully, but unless this is done often, then the wear shouldn't be significant.
In point 3 above, where there is a different surface that parking brake shoes/pads press against, the metal surface wont be getting cleaned/derusted under normal operation of the brakes. Rust can build up and abrade the pads/shoes while driving, causing wear.
Additionally the parking brake friction material, while not being used to slow the vehicle down causing wear, are still in a hostile environment with constant changes in heat. This can cause the friction material to break down and eventually require replacing.