Semi Truck 5th Wheel Fixed vs Sliding – Differences and Applications

Over the years, you might have heard conflicting opinions when it comes to whether a fixed or sliding fifth wheel is the best for a semi. It’s a complex topic and there’s a lot to consider. Here’s a closer look at what fifth wheels are and the pros and cons of a fixed versus a sliding fifth wheel.

What Is a Fifth Wheel?

The term “Fifth Wheel,” follows from the days of horse-drawn wagons that had 4 wheels. The “5th wheel” was the front axle pivot mechanism that allowed the front axle of the wagon to be turned side to side, steering the wagon, as pulled by the horse(s). The semi-tractor now does both: the pulling the horses used to do, and; the steering the front axle of the wagon did. The device that allows the wagon/trailer to turn is still called the 5th wheel. Many other trucking terms follow from the days when wagons were called ‘rigs,’ and wagon drivers were known as ‘teamsters’ because they drove the team of horses pulling the wagon. Freight transportation is as ancient and historical as trading and commerce.

The fifth wheel joins together the 2 vehicles, tractor and trailer, to compose 1 combination vehicle, the semi truck, or the ‘rig.’

A Fifth Wheel is the mechanism that connects the tractor to the trailer. It allows the articulation between the combined 2 vehicles, the ‘rig,’ facilitating steering the vehicle. It spreads the weight of the freight load between tractor and trailer.

Photo of a Fifth Wheel mounted on the frame rails of a tractor.

Photo of where the Fifth Wheel is mounted onto a tractor

Identify Fixed vs Sliding

A Fixed Fifth Wheel is mounted to the frame of the tractor without the ability to move it forward and backward along the frame rails.

Photo of a Fixed fifth wheel installation.

A Sliding Fifth Wheel is mounted to the frame with the ability to slide the 5th wheel forward and backward along the frame rails.