Rotors are attached to the wheel bearing or hub and rotate with the wheel and tire. Each one is surrounded by and centered in the caliper with the brake pads. Rotors get a lot of abuse from normal day-to-day wear and tear.
At night, metal rotors become covered with surface rust. When you drive your car again in the morning, the brake pads remove the rust. If a vehicle sits for several days, you may hear a low scraping or grinding noise, especially when going backward, because the brake pads are removing more built-up rust.
What Causes a Rotor to Warp
Exceeding Operating Temperature
As the rotors wear down and get thinner, the amount of heat they absorb rises. Each rotor has a maximum operating temperature. A rotor will warp and become deformed when that temperature is exceeded. As a result, the rotor’s surface is no longer uniform.
When the brake pads connect with a warped rotor, they pulse in and out of the caliper. The pulsing generates vibrations you can feel in the steering wheel for vehicles with front disc brakes. You’ll feel it in the brake pedal or driver’s seat if your vehicle has rear disc brakes. When you feel these types of vibrations, get the rotors checked and measured.
Manufacturers publish the original thickness and the discard thickness of their rotors. You have to measure the thickness with a precision measuring tool called a caliper if you want to know for sure that a rotor needs to be replaced.
Take a thickness measurement at different spots around the rotor. Together, these measurements will determine if the rotor is below the discard thickness. If the rotor is warped and doesn’t have too much wear, you can smooth it out on a brake lathe.
A hard panic stop can cause a rotor to warp, especially with old and worn rotors. During a panic stop, the steering wheel suddenly vibrates during braking. Because the front brakes perform about 70% of the braking, front rotors often warp long before the rear ones.
Under normal driving conditions, you may not realize it is time to replace the rotors. Once you’ve replaced the brake pads twice, the rotors will probably measure below discard thickness. To ensure optimal braking and safety, some vehicle manufacturers require rotors to be replaced every time the pads are replaced.
About Goodyear Brakes
Goodyear Brakes manufactures premium quality brake bundles, calipers, rotors, brake pads and all the hardware required to successfully install brakes, all backed by a national warranty, decades of production experience and one of the best-known names in automotive excellence. The brake pads are manufactured in the USA using a proprietary green production process by a company with more than 50 years of experience in friction science. The Goodyear Brakes product line is available through Goodyear Brakes at Amazon, CarID, Buy Brakes and AutoAnything.
Goodyear (and Winged Foot Design) and Blimp Design are trademarks of The Goodyear Tire & Rubber Company used under license by FDP Virginia Inc., 1076 Airport Road, Tappahannock, VA 22560, USA. Copyright 2020 The Goodyear Tire & Rubber Company. Goodyear Brakes and FDP Virginia are not responsible for its products when they are subjected to improper applications, installation, or accident.
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