What component of a tire assembly prevents dirt and moisture from entering the valve body?

The valve cap is designed to prevent dirt and moisture from entering the valve body of a tire assembly. It screws onto the top of the valve stem and creates a seal, keeping contaminants out that could potentially interfere with the valve's function. This is particularly important because moisture or debris entering the valve can cause air loss or damage to the valve mechanism, leading to tire pressure issues.

The other components play different roles in tire functionality. The tire bead connects the tire to the rim, ensuring a proper fit, while the rim supports the tire and maintains its shape. The valve stem is the part through which air is added to or released from the tire but is not designed to actively keep out dirt and moisture like the valve cap does. Thus, the primary function of the valve cap is to protect the integrity of the valve and maintain safe tire operation.