Brake rotors will not last forever, they wear down a little bit every time the brake pedal is applied. How fast the rotors wear depends on a lot of variables including the type of brake pads, quality of the materials, how fast the rotors cool down, driving style, exposure to moisture and road salt.

Most original equipment brake rotors used to be designed with enough thickness to last at least two or more pad replacements. Most newer cars have thinner rotors to save weight and could be worn to the minimum by the first time the brake pads need to be replaced. Normally both rotors need to be replaced because they will usually have the same amount of wear. Even if one side is "good enough" it is wise to replace both brake rotors at the same time to maintain even braking as any difference in rotor thickness will cause the brakes to pull to one side.

If a brake rotor has minimal lateral runout it should wear evenly, otherwise the result will be thickness fluctuations which will create vibration. It only takes .001 inches of thickness variation to cause a noticeable pedal vibration. Excessive runout can be solved by installing tapered shims between the brake rotor and hub, or by resurfacing the rotor with an on-car brake lathe. Runout can also be corrected using a conventional bench lathe, but it is a much more difficult procedure. Cleaning the face of the hub and the inside of the rotor hat with a drill powered brush before installation will remove dirt, rust, or any particles that can create gaps between the rotor and hub. Rotor distortions can be caused by improper tightening of the lug nuts. Uneven torque between lugs can twist the rotor hat, causing the disc section of the rotor to wobble.

Friction from the brake pads against the brake rotors generates a lot of heat. Overheating brakes will shorten the life of both the pads and rotors. Vehicles that spend most of their time in stop-and-go traffic, pulling a trailer, or mountain driving will wear out the brakes much sooner than vehicles which are driven mostly in light traffic. Hard spots and discoloration can also develop from excessive heat. These hard spots yield uneven wear across the brake disc. Trying to shave them off by resurfacing will not cure the problem because hard spots extend below the surface, the only fix is rotor replacement.

If your brake rotors have sufficient metal remaining with no hard spots, cracks, severe grooving or rusting, then the rotors could be resurfaced. Some have the opinion that unless the brake rotors have surface issues needing to be fixed, the rotors should not be resurfaced every time the pads are replaced. If the brake discs are still smooth they may not need to be resurfaced, but most professional brake mechanics will not install new brake pads without resurfacing the rotors. Resurfacing restores a flat and even surface that minimizes vibrations and allows for maximum brake pad friction. Installing new pads on a grooved brake rotor will not allow the pads to make full contact with the brake disc, and eventually the pads will wear down and fully seat themselves into the contours of the brake discs, but this will only decrease the life of the brake pads.

As inexpensive as rotors are now, it is affordable enough to simply replace the rotors rather than paying to resurface them. New brake rotors should be ready to install right out of the box. There is no need to resurface them as this may actually produce runout and will reduce their service life. If your vehicle originally included brake rotors with a separate hub and disc (composite rotors) they can safely be replaced with cast iron brake rotors. Cast rotors are more rigid than composite rotors, but they may slightly affect steering and handling on some vehicles. For those customers who are interested in increased brake performance and safety, we recommend premium brake rotors over the standard replacement brake rotors.
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