What prevents air from leaking out between the two halves of a split wheel assembly?

The use of an O-ring in a split wheel assembly is critical for maintaining airtight integrity between the two halves. The O-ring is designed to create a seal that effectively prevents air from leaking out when the wheel assembly is under pressure. This seal forms a tight barrier at the joint where the two halves of the wheel come together, ensuring that any pressurized air remains contained within the assembly, which is essential for proper tire inflation and function.

In many applications, O-rings are favored because of their flexibility and ability to conform to slight variations in surface contours, providing a reliable seal even under dynamic conditions. This characteristic is paramount in a wheel assembly where pressure changes can occur due to inflation or changes in temperature.

The other options do not serve this specific sealing purpose in a typical split wheel assembly. While a retaining ring does help hold parts together, it doesn't provide a direct airtight seal. A valve seal is usually associated with tire valve integrity but is not relevant to the division between wheel halves. Grommets can provide protection and stability for wires and hoses but are not utilized in the context of creating an airtight seal in wheel assemblies.