Semi Trailers versus Full Trailers

Jim McCormack
Freightliner trucks

What is the difference between a semi trailer and a full trailer?

Pretty simple – a full trailer is fixed to the tractor unit whereas the semi is detachable, and certainly on American roads semi trailers dominate.

But why?


Semi Trailer Advantages



The major advantage of a semi trailer is flexibility, but there are several reasons why semi trailers have this flexibility and some you may not already know: Semi trailers can be coupled and detached easily and fast, which provides for shunting during loading and for trailers to be trunked between loading depots;

If the tractor breaks down then another tractor can be coupled and the load continue on to destination without lengthy delay (it takes just as long as is needed to get a replacement tractor unit to the broken down units location); A semi trailer can be attached to another semi trailer using a dolly – this is more common overseas in countries such as Australia where several trailers will be attached to form a road train;


Tugs, yard dogs or shunts can be used to shift semi trailers around loading and docking facilities – these are not full tractor units for use on the road, but they are far cheaper and easier to handle than a full tractor unit; A semi trailer is easier to reverse than a full trailer as there is only one turning point at the coupling compared to a full trailer which has two;


A semi trailer also has a smaller turning circle compared to a full trailer;  Semi trailers have longer cargo beds which means they can transport longer loads; Semi trailers generally can haul a greater load than a full trailer; Semi trailers provide a better load ratio between tare and laden weight;  In snow, a semi trailer tends to have more weight on the drive axles of the tractor unit which gives better traction and road handling characteristics in adverse weather conditions.

The Bad News

Semi tractor trailers have a center of gravity which tends to be higher than full trailers which makes them prone to tipping over compared to rigid trailer construction; Semi trailers are prone to jackknifing because they are articulated, i.e. do not have a fixed but movable attachment between tractor and trailer; and Semi tractor units have zero use on their own.