Why Is There a Notch in My Brake Rotor? Understanding Mill Balancing

100% Mill Balanced PowerStop Brake Rotors notch in rotor



A Mill Balanced Notch in Brake Rotors Reduces Vibration While Driving

Some may notice little notches on the side of their new brake rotors. Those milled areas are a result of the process used to balance rotors, called “mill balancing”. A mill balanced brake rotor reduces vibration and is meaningful to the whole brake system.

Brake rotors are made from castings. Any casting that has surfaces that are not machined (such as the cooling vanes inside of a vented rotor) are subject to imbalance. An imbalance is when one side of a rotor is heavier than the other side. Imbalanced brake rotors can cause a vibrating feeling to the driver and passengers when a vehicle is in motion. Also, imbalanced brake rotors lead to accelerated bearing wear.

PowerStop prevents imbalance by mill balancing 100% of our brake rotors. A mill balancing machine is a single piece of equipment that spins the brake rotor at high speeds and measures for imbalance as it is spinning. If imbalance is present, the machine uses milling blade and notches the “heavy” side of the rotor on the edge. The notching is placed in between the friction contact areas to not interfere with the brake pads during operation. The machine mills out just enough material that the weight of the milled material equals the amount of imbalance. The machine then spins the brake rotor at high speeds again to verify the balance of the brake rotor.

It is worth noting that some brake rotors may not have the notch on the edge. The brake rotors were still checked for balance. However, the balance checked out OK and they were passed through to the next phase of manufacturing.

If the rotor needs it, mill balancing is the key to having a pleasant, enjoyable, and safe ride!

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