Scoring on brake disc or brake rotors are caused by friction when the material on brake pads have been worn down to the metal.
The metal of the brake pads then makes contact with the brake rotors or brake disc and then causes the scoring.
Riding the brakes too much can also heat the brake rotors up and lead to scoring or overheated brake rotors as well.
Bad rotors can sound like a grinding sound, high pitched squeak, squealing or squeaking sound when you apply the brakes.
Warped rotors tend to make a high pitched squeak and severely worn out rotors usually make a scraping sound.
The signs that you need new brake rotors are the brake rotors are warped, the brake rotors are cracked, the brake rotors are getting thin or the brake rotors are scored or have grooves in them.
Also squealing sounds from the brakes, steering wheel vibrating when braking, brake pedal pulsates when braking, banging sounds when braking or large edge on the brake rotors surface.
Brake rotors should last between 50,000 miles to 70,000 miles although some brake rotors last 100,000 miles or more.
Brake rotors should be replaced every 50,000 miles to 70,000 miles or when they become worn down or cracked or warped.
And some brake rotors and brake drums can last 100,000 miles or more.
I always replace my brake rotors after every 2 brake pad changes which can be every 5 years or so depending on the mileage I drive.
Brake rotors that have gone bad are usually either warped, cracked or just have gotten thinner as the brake pads wear them down.
Most brake rotors will easily last 100,000 to 200,000 miles and sometimes longer.
If you notice any cracks in the brake rotors or the brake rotors are warped or have gotten thin then you should replace them.
I have had a brake rotor shatter before when I failed to replace a cracked brake rotor so if you see any cracks developing in the brake rotor then replace them.
Brake rotors should be replaced in pairs.
Some people need to replace their brake rotors every 80,000 to 150,000 miles and some people may need to replace the brake rotors after every 4 sets of brake pads.
If you do a lot of towing with your vehicle then you may need to replace your brake rotors much sooner than someone who does no towing or hardly any towing at all.