What component of a tire assembly permits air, under pressure, to enter the tire, but prevents it from escaping?

The valve core is a vital component of a tire assembly as it plays an essential role in maintaining air pressure within the tire. It consists of a small, spring-loaded mechanism that allows air to enter the tire when the valve stem is activated (such as when inflating the tire) and simultaneously prevents air from escaping when the valve is closed. This function is crucial for ensuring that the tire remains properly inflated, which directly impacts vehicle performance, safety, and fuel efficiency.

The valve stem, while critical in providing access to the valve core for inflation and deflation, does not perform the function of retaining air on its own; it merely facilitates the connection to the tire. The rim serves as the structural portion of the tire assembly that holds the tire in place but does not retain air. The tread is the outer surface that comes into contact with the road; although it contributes to grip and handling, it does not function in sealing the air within the tire. Therefore, the valve core is precisely the component responsible for allowing air into the tire while preventing it from escaping.