The trailer bed plate, also known as a rubbing plate, is a thick, horizontal steel plate fitted to the underside of the trailer's front end. It forms the primary contact surface with the tractor unit's fifth wheel, supporting vertical load while allowing articulation between the two units.
During coupling and normal operation, the bed plate rests directly on the fifth wheel. This interface must be smooth and durable, enabling controlled movement while transferring imposed load from the trailer to the tractor unit.
The bed plate also incorporates the kingpin, which engages with the fifth wheel locking mechanism to secure the connection. Together, the bed plate, kingpin and fifth wheel form the core load-bearing and articulation system of an articulated vehicle.
Bed plates can be partial width, fitted between the chassis I-beams, or full width. Full width designs provide increased wear protection and distribute load more evenly across the front structure of the trailer.
As a high-friction contact surface, the bed plate is subject to wear over time. In operation, it typically works with a greased or low-friction fifth wheel surface to reduce resistance and extend component life.
Frequently Asked Questions
Is a bed plate the same as a rubbing plate?
Yes. Bed plate and rubbing plate are commonly used interchangeably to describe the same steel contact plate fitted to the front underside of the trailer.
What type of grease should be used on a fifth wheel?
A high-pressure fifth wheel grease is typically used to reduce friction between the fifth wheel and the trailer bed plate. It must be suitable for heavy load contact surfaces and resistant to wash-off. Always follow the fifth wheel manufacturer's specification.
Why are trailer bed plates available in full width and partial width designs?
The difference is primarily related to coupling conditions. A partial width bed plate is typically sufficient when the tractor unit reverses in line with the trailer. However, if coupling occurs at an angle, the fifth wheel can contact and damage exposed chassis components. A full width bed plate provides additional protection by covering a wider area, reducing the risk of damage during angled or restricted access coupling.
