Classification of a Semitrailer or Gooseneck Trailer
The Compulsory Specifications for Motor Vehicles determine the type of category under which a trailer, irrespective of its design, will be categorised.
VC8026 Compulsory Specifications for Motor Vehicles of Category O1/O2
single-axle trailers, other than semitrailers, with a maximum mass not exceeding 0.75 t.
trailers other than category O1, with a maximum mass not exceeding 3.5 t.
trailer having no front axle and so designed that at least 15 % of its tare is super-imposed on and borne
by a vehicle drawing such trailer
A category O1 trailer cannot be a semitrailer.
If it is designed in such a way that at least 15% of the unladen mass is superimposed onto the coupling (pony trailer), then it is classified as category O2, even when the gross vehicle mass is below 0.75 t.
A category O2 trailer can be a semitrailer (Gooseneck trailer).
The compulsory specification (VC8026) makes no reference to the load carried by the wheels.
In this case the GVM (maximum 3.5 t) determines the category of the vehicle. The load carried by the wheels is only relevant to determine the braking forces required.
A category O2 trailer cannot be heavier than 3.5 t GVM, irrespective of its design.
VC8027 Compulsory Specifications for Motor Vehicles of Category O3/O4
a) category O3
trailers with a maximum mass exceeding 3,5 metric ton but not exceeding 10 metric ton; and
b) category O4
trailers with a maximum mass exceeding 10 metric ton
Semi-trailers and centre-axle trailers.
In the case of a semitrailer or a centre-axle trailer, the maximum mass to be considered for classifying
the trailer shall be the static vertical load transmitted to the ground by the axle, or axles of the semitrailer,
or centre-axle trailer, when coupled to the towing vehicle and carrying its maximum load.
Trailers of category O3 or O4 can be semitrailers.
The compulsory specification (VC8027) makes a clear reference to the classification of such a semitrailer, whereby the static vertical load transmitted to the ground through the wheels.
The wheel load (GA/GAU) is therefore the load determining whether a semitrailer or centre-axle trailer is of category O3 or O4, and not the GVM.
A category O2 trailer cannot exceed the GVM or A/AU limit of 3 500 kg
A semitrailer with a GVM of 15 000 kg and an A/AU rating of 10 000 kg will be classified as O3 trailer.
A semitrailer with a GVM of 15 000 kg and an A/AU rating of 10 200 kg will be classified as O4 trailer.