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

100% Mill Balanced Power Stop Brake Rotors

A Mill Balanced Notch in Brake Rotors Reduce Vibration While Driving

A mill balanced brake rotor reduces vibration. Some may notice little notches on the side of the rotors. Those milled areas are a result of the process used to balance rotors. This characteristic serves a meaningful purpose to the 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. When a brake rotor is imbalanced, the vehicle is driving down the road, the imbalance of the brake rotor can cause a vibration in the vehicle that is noticeable to the driver and the passengers. Imbalanced brake rotors also have the potential to accelerate bearing wear.

Power Stop prevents imbalance by mill balancing 100% of their brake rotors. A mill balancing machine is a single piece of equipment that spins the brake rotor at a high rate of speed and measures for imbalance as it is spinning. If imbalance is present, the machine has a milling blade that comes out and notches the “heavy” side of the rotor on the edge – in between the friction contact areas so it does not interfere with the brake pads 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 a high rate of speed 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.

A mill balanced is the key to having a pleasant, enjoyable, and safe ride!

Don’t just stop… Power Stop!
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