What is an HGV trailer step-frame, swan-neck or goose-neck?

A step-frame trailer is a trailer chassis where the deck height drops behind the front section to create a lower main platform, allowing increased internal height for taller loads or double deck configurations.

Step-frame is the technical term for this chassis layout. The terms swan-neck and goose-neck are alternative names for the same overall feature: a raised front section, a stepped transition, and a lower rear deck.

The raised front section — positioned over the tractive unit — sits at a height governed by the fifth wheel. In UK operation, fifth wheel height is typically around 1250mm from ground level. When combined with the structural depth of the neck itself (commonly around 200mm), the resulting front deck height is typically in the region of 1450mm from ground level.

Behind the step, the main deck can be significantly lower. On standard running gear such as 17.5 inch twin tyres, floor heights can reduce to around 880mm from ground level, creating a substantial step between the front and rear sections.

In more specialised configurations using independent suspension and boxed wheel arches, the lower deck height can be reduced further, in extreme cases to approximately 250mm from ground level.

This stepped design increases usable internal height within overall vehicle height limits, making step-frame trailers common in high-cube and double deck operations.

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