How is a vehicle supported while being towed by a truck tractor?

A vehicle being towed by a truck tractor is supported primarily by a kingpin. The kingpin is a crucial component that connects the trailer to the truck tractor, allowing for a secure and stable attachment. It is a strong metal pin that is mounted on the trailer and fits into a corresponding locking mechanism in the truck tractor's fifth wheel. This connection allows the truck tractor to transfer both weight and towing forces effectively to the trailer, maintaining stability during travel.

While other components like the front axle and trailer hitch do play important roles in vehicle dynamics, they do not directly support the trailer in the same manner as the kingpin. The rear end of the truck also does not support the trailer but plays a role in the overall balance and functioning of the vehicle when towing. Understanding the function of the kingpin helps in comprehending how the towing system operates, ensuring safe and efficient towing practices.