A cant rail on a trailer is the longitudinal structural member located at the top edge of the body side, forming the junction between the side structure and the roof.
The cant rail runs the full length of the trailer from the front bulkhead to the rear frame and supports the upper body structure. Its design and role vary depending on body type, particularly between curtainsiders and box vans.
In simple terms, the cant rail forms the top side member of the body. On a curtainsider it is a primary structural component, whereas on a box van it is typically an aluminium section used to integrate the side panels and roof structure.
Where is the cant rail located?
The cant rail is positioned along the upper edge of each side of the trailer body, directly below the roof structure. It runs continuously along both sides of the trailer.
While the position is consistent across body types, the construction and purpose of the cant rail differ depending on the overall body design.
What does a cant rail do?
The cant rail forms the upper longitudinal side member and supports components connected to the roof and upper side structure.
- Structural support: Contributes to the strength and stability of the upper body.
- Component mounting: Provides a mounting point for curtain track, roof elements or roof sticks depending on the body type.
- Body integration: Connects the side structure to the roof structure.
- Operational function: Influences access and usability during loading and unloading on certain body types.
Cant rail on curtainsiders
On a curtainsider, the cant rail is a strong main steel structural member, typically of box or beam construction.
It acts as a mounting member for the curtain track, which supports the curtain pelmet. This means it must provide both structural strength and consistent support for the curtain system.
The cant rail may be supported by side posts, but more commonly it spans with minimal or no intermediate support to maximise side access during loading and unloading.
This requirement for strength over long spans makes it a critical structural component of the curtainsider body.
Cant rail on box vans
A box van cant rail is typically an aluminium extruded section rather than a heavy steel structural beam.
It is often radiussed to support a smoother body profile and improved aerodynamics. The section is designed to bolt to the side panels and provide a formed detail to house the roof sticks.
Although it is generally less structurally demanding than a curtainsider cant rail, this reflects the inherently stronger, enclosed construction of a box van body.
Why the difference matters
The term cant rail is used across different trailer body types, but the component itself is not identical in design or function.
On a curtainsider, it is a major structural steel member that also supports the curtain system. On a box van, it is typically an aluminium joining section that integrates the side panels and roof.
This distinction is important when considering design, maintenance, repair or replacement.
Why cant rail condition matters
Damage or deformation to the cant rail can affect both structural integrity and day-to-day operation.
On curtainsiders, this may affect curtain track alignment, pelmet support and overall rigidity. On box vans, it can affect the fit between side panels and roof structure, including support for roof sticks.
Regular inspection and timely repair are important to maintain safe and reliable operation.
