Besides replacing, what is a common action required to maintain motorcycle wheel bearings?

Answer: B — Greasing them regularly

Regular greasing of motorcycle wheel bearings is crucial for maintaining their performance and longevity. Wheel bearings endure significant stress as they facilitate the rotation of the wheels, which can result in wear over time. Applying fresh grease helps reduce friction between the moving parts, thus preventing excessive wear and overheating, which can lead to bearing failure. Properly greased bearings also ensure smooth wheel rotation, contributing to better handling and stability of the motorcycle during operation. It's a proactive maintenance measure that can extend the lifespan of the bearings and enhance overall safety. While other maintenance actions are important for the motorcycle's performance, such as inspecting tire tread depth and adjusting tire pressure, they do not directly pertain to the condition of the wheel bearings themselves. Thus, greasing the bearings is the most relevant action to maintain their function effectively.