Do I need to Turn Rotors when changing Brake Pads What does Resurface Rotors Mean?

Should you replace or resurface your rotors when doing a brake job?

Like brake pads, brake rotors don’t last forever. The rotors wear every time the brakes are applied. The rate at which rotors wear depends on a lot of variables: the type of brake pads on the vehicle, the metallurgy (hardness and quality) of the castings, how efficiently the rotors cool themselves, the type of driving the vehicle is subjected to, the braking style of the driver (aggressive or easy) and exposure to moisture and road salt.

Semi-metallic brake pads usually contain a very high percentage of chopped steel fiber, so they typically cause more wear on the rotors than most ceramic or nonasbestos organic (NAO) brake pads. On vehicles where rotor wear is a problem, switching to a “softer” friction material (such as ceramic or NAO) may solve the problem — provided there’s a choice of friction materials available for the application.

The quality of original equipment rotors can vary from excellent to questionable. Most carmakers insist rotor quality is extremely important. After all, the rotors are part of the brake system and safety is paramount. Yet some original equipment rotors come from the factory with hard spots, inclusions, impurities and other junk in the cast iron that undermines their durability, wear resistance and performance. Good metallurgy is critical because it affects the friction qualities of the rotor as well as its strength, hardness, sound characteristics and even its corrosion resistance.

As a rule, most original equipment rotors used to be designed with enough thickness to go two or more pad replacements. But on some cars today, the rotors are thinner to save weight and cost. Consequently, the rotors may be worn down to minimum thickness specifications (which is usually marked on the casting itself) by the time the first set of brake pads need to be replaced — or even sooner in some cases.

The minimum thickness specification is an important dimension because it is the minimum thickness that provides safe braking. As a rotor wears and becomes thinner, it has less mass. This reduces the rotor’s ability to absorb and dissipate heat. It also reduces the strength of the rotor, increasing the risk of cracking or even breaking (rotor failure).

That’s why the thickness of the rotors should always be measured every time the brakes are serviced. If a rotor is worn down to the minimum thickness specification, or cannot be resurfaced without exceeding the dimension, it must be replaced. In some states, this is the law.

Great article on rotor science:
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