Final answer:
Corrosion is best removed by chipping it from the brake drum and cleaning the hub with a wire brush, which is crucial for maintaining optimal brake system performance.
Step-by-step explanation:
The substance that is best removed by chipping it from the brake drum and then cleaning the hub with a wire brush is corrosion.
Corrosion usually appears as a buildup of rust and other materials on metal surfaces. It is essential to remove it to maintain the brake system's optimal performance. To deal with brake drum corrosion, you should first chip away the larger pieces of rust. Then, using a wire brush, clean the remaining corrosion from the surface to ensure a smooth and clean contact area for the brake components.