Which part is essential when inspecting tires and wheels?

When inspecting tires and wheels, the valve stem and cap play a crucial role in maintaining proper tire pressure. The valve stem is the component that allows air to enter or exit the tire. If the valve stem is damaged or defective, it can lead to air leaks, which can cause underinflated tires. Underinflation can lead to various safety issues, including reduced traction, increased tire wear, and potential tire failure while driving. The valve cap also serves an important function by protecting the valve stem from dirt, debris, and moisture, which can compromise its function.

While shock absorbers, air compressors, and brake pedals are all important components of a commercial vehicle, they pertain to different aspects of the vehicle's performance and safety. Shock absorbers are related to the vehicle's suspension system, air compressors deal with air supply for various systems, and brake pedals are related to the braking functionality, but they do not directly impact the integrity of the tires and wheels during inspection. Thus, the valve stem and cap are essential elements to check when focusing on tire and wheel inspection.