With the Saab disc brake rotors having the wheels directly attached to them, the stopping power of your vehicle is guaranteed as long as the rest of the braking system is functioning as it was designed to. The disc brake rotors are the receiver of the friction the brake system creates in order to stop your Saab. The brake rotors have two flat disc-like surfaces on them which are made of a material that is harder than what the brake pads are made from. Because they are harder, it is the brakes pads that will wear down when the friction is created in the braking process. The braking process on your Saab transfers the hydraulic fluid from the reservoir in your brake master cylinder to the brake caliper moving the piston out. It is this piston that is the force behind the creation of the friction between the disc brake rotors and discs and the brake pads on your Saab. As the brake pads wear out, the length the piston has to travel increases which decrease the level of hydraulic fluid in the reservoir in the master cylinder. This is why the owner of the vehicle will know it is time to replace the brake pads. If that is not noticed or ignored the backing plate where the brake pads are mounted will come in direct contact with the Saab brake rotors and discs which will create grooves in the previous smooth surfaces on them. The brake rotors will then have to be resurfaced or replaced during the next brake job increasing the cost of their repair procedure that the owner will then have to pay for.