What aspect is essential to check regarding the bus mirrors?

The aspect of checking bus mirrors that is essential is ensuring they allow visibility of the front of the rear tires and surrounding traffic. This is critical for safe driving, as it enables the driver to monitor the area immediately around the bus, ensuring that there are no obstacles or hazards that could lead to an accident, especially when the bus is making turns or changing lanes.

Visibility of the front of the rear tires helps in assessing the position of the bus concerning the road, other vehicles, and pedestrians. It is particularly important for a larger vehicle like a bus, which has considerable blind spots. This comprehensive visibility is key to ensuring the safety of both the bus passengers and others using the road.

While it's certainly important for mirrors to be clean and free of dirt for visibility, relying solely on cleanliness without ensuring the mirrors give a proper field of view would not provide the necessary safety oversight. Similarly, while sun protection is useful for reducing glare, it is not a fundamental requirement for the functionality of mirrors in terms of safety and traffic awareness.