What is the primary function of the fifth wheel on a combination vehicle?

The primary function of the fifth wheel on a combination vehicle is to securely connect the trailer to the tractor and allow for articulation while turning. The fifth wheel serves as a pivotal point that enables the truck's cab (tractor) to maintain a strong connection with the trailer while also allowing for the necessary movement as the vehicle negotiates turns. This design ensures that the trailer can pivot freely in relation to the tractor, which is crucial for maneuverability, particularly in tight spaces or when navigating curves.

By providing both a secure attachment and the ability to articulate, the fifth wheel system enhances the overall stability and control of the combination vehicle during operation. While it also bears some of the trailer's weight, that is a secondary aspect to its more critical role in maintaining the joint connection and facilitating movement between the truck and trailer.