Oscillating fifth wheels are available in both fully-oscillating and semi-oscillating models.  The fully-oscillating fifth wheel provides both front-to-rear and side-to-side oscillation (articulation) between the tractor and semi-trailer.  The semi-oscillating version provides only front-to-rear oscillation.

FULLY OSCILLATING

A fifth wheel designed to provide both front-to-rear and side-to-side oscillation between the tractor and semi-trailer; for vehicles that operate on rough and uneven terrain (mining, logging, etc.).  The oscillation is provided by the use of an undercarriage employing both transverse and longitudinal shafts. The side-to-side oscillation pivot point is located below the fifth wheel bearing surface.

For applications where minimizing torque and twist transfer through the fifth wheel is beneficial. Used where center of gravity is equal to or below fifth wheel height.

SEMI-OSCILLATING

The standard over-the-road fifth wheel is the semi-oscillating type which oscillates (articulates) about an axis perpendicular to the vehicle centerline to accommodate for normal road variations ( inclines, bumps, etc.).