Calculating capacity of trailer coupling
The Heavy Vehicle Calculator is a tool that can be used to find out whether your trailer couplings have sufficient capacity.
The Heavy Vehicle Calculator calculates whether the trailer couplings in your vehicle combination have sufficient capacity, given the weights that the vehicle combination have during a particular transport.
When can you use the calculator?
The calculator is a tool that can be used when
- you need to comply with Section 4-6 of the Regulations relating to the Use of Vehicles ("forskrift om bruk av kjøretøy") on lorries and tractor units with a connected trailer or trailers (vehicle combinations, modular vehicle combinations, and heavy abnormal transports) that are approved according to Section 10-9 of the Regulations relating to the Approval of Motor Vehicles and their Trailers ("bilforskriften")
- you have a foreign vehicle combination that will be driving in Norway
- you are combining Norwegian and foreign vehicles in one vehicle combination
You can use the calculator when the vehicle combination has
- a lorry or tractor unit in category N2 or N3
- one or more trailers of category O3 or O4
- trailer couplings that are approved as described in Section 4-6 (4) of the Regulations relating to the Use of Vehicles
The driver is responsible
The driver is responsible for ensuring that the correct data from the trailer coupling specifications are used.
The driver must also ensure that the actual weights entered in the calculator are equal to or higher than the weighed weights, but do not exceed the maximum permitted weights for the individual vehicles, the entire vehicle combination or the road.
All values for weights and capacities must follow the terms and definitions in the Regulations relating to the Use of Vehicles ("forskrift om bruk av kjøretøy").
If you often drive the same vehicle combination
If you often drive the same vehicle combination, it may be a good idea to enter the highest actual weights that place the greatest load on the trailer couplings.
Important terms
Below you will find terms that are useful when using the calculator. In addition to these terms, you should also be familiar with the definitions in the following regulatory documents:
- the Road Traffic Act
- the Regulations relating to the Use of Vehicles
- the Regulations relating to the Approval of Motor Vehicles and their Trailers (bilforskriften)
- international rules and regulations
We use the word "weights" in the plural to avoid repeating total weight, axle weight and vehicle combination weight under each main group, such as maximum technical weight, maximum authorised weights and so on. This grouping of weights is found both in Norwegian regulations since 1969 and in international regulations.
When a vehicle is approved and registered in Norway, the maximum authorised weights are usually set equal to the maximum technical weights specified by the manufacturers.
| Term | Explanation |
|---|---|
| The vehicle's maximum technical weights | The maximum weights technically permissible, i.e. for which the vehicle is designed and guaranteed by the manufacturer (also known as design weights). |
| Maximum authorised weights | The maximum weights for which a vehicle has been approved and registered by the authorities (country of registration). |
| Actual vehicle weights | The actual weights of the vehicle at a particular time, including load and driver. |
| Permissible weights on public roads | The actual weights that are permissible on an individual stretch of road according to Regulations relating to the Use of Vehicles or other public regulations. |
| Vehicle combination | Vehicle combination consisting of a motor vehicle connected to a drawbar trailer (full trailer), centre-axle trailer (simple trailer) or semitrailer. |
| Modular vehicle combination | Vehicle combinations consisting of a motor vehicle of category N2 or N3, connected to more than one trailer. Permitted modular vehicles are described in Section 5-5 (2) of the Regulations relating to the Use of Vehicles (Lovdata, Norwegian only) |
| Abnormal transports | The calculator can be used for heavy abnormal transports. These have higher actual weights than what is permitted for normal transports on public roads. |
| Trailer couplings | Trailer couplings are found both on the towing vehicle and on the vehicle being towed. The term includes the coupling itself and the details of the mounting system attaching it to the frame, such as the drawbar, drawbeam and fifth-wheel mounting system with or without a slider. |
| Characteristic values for capacity (D, Dc, V, S, Av and U) | Maximum forces for which the trailer couplings are approved. These values are defined in UN Regulation 55 (unece.org). |
| Coupling forces (D, Dc, V, S and U) | The calculated forces applied to the trailer coupling(s) by the weights of the vehicle combination or modular vehicle combination while in use. |
Terms for trailer coupling
This calculator and the Regulations on the use of vehicles use the term trailer coupling. Alternative terms in use often differentiate between the parts found on the towing vehicle and the parts found on the trailer.
Rules and regulations
Excerpts from the Regulations relating to the Use of Vehicles - unofficial translation
In the event of contradiction or inconsistency between the language versions, the Norwegian version shall apply.
Section 4-2 Towing of trailers and trailed equipment
3. A motor vehicle must not be used to tow a trailer or trailed equipment if its coupling device is not of a type and size that has been approved for the trailer or trailed equipment in question, or if the coupling device on the trailer or trailed equipment is not compatible with the coupling device on the motor vehicle. A trailer in a modular vehicle combination must not be used to tow another trailer unless its rear coupling device is of a type and size which has been approved for that trailer, or if the next trailer's coupling device is not compatible with the coupling device of the trailer in front.
4. A motor vehicle must not be used to tow a trailer, trailers in a modular vehicle combination or trailed equipment with an actual total mass that exceeds the mass limit for trailers for the motor vehicle. A trailer in a modular vehicle combination must not be used to tow another trailer with an actual total mass that exceeds the mass limit for trailers for that trailer. The maximum vehicle combination mass set for the motor vehicle must not be exceeded. A vehicle combination or modular vehicle combination must not be used if the characteristic values for capacity for the trailer coupling and/or the vehicle are exceeded.
Section 4-6 Calculation of coupling forces for trailer couplings (and their attachment):
(1) For motor vehicles N2 and N3 connected to trailers O3 and O4, calculations may be made of the coupling forces acting on the trailer coupling(s) by the weights of the vehicle combination or modular vehicle combination in use.
(2) The calculations shall be made in accordance with UN Regulation 55, Amendment Series 01, Supplement 07 or later, or in accordance with the formulas in Annex 2.
Where the UN regulation states that technical masses are to be used, the vehicles' actual masses may be used to calculate the coupling forces.
(3) In addition to the definitions following from Sections 1-2 and 5-2, the following terms shall be understood as follows:
- Trailer couplings, both on the towing vehicle and on the towed vehicle, include details of the mountings system attaching the coupling to the frame, such as the drawbar, drawbeam and mounting plates with or without a slide.
- Characteristic values for capacity (D, Dc, V, S, Av and U): Maximum forces for which the trailer couplings are approved.
- Coupling forces (D, Dc, V, S and U): The calculated forces applied to the trailer coupling(s) by the masses of the vehicle combination or modular vehicle combination while in use.
(4) Calculations may be used if the trailer couplings are:
- type-approved and installed in accordance with Directive 94/20/EC of the European Parliament and of the Council of 30 May 1994, as amended, on mechanical coupling devices for motor vehicles and their trailers and their attachment to such vehicles, or
- type-approved and installed in accordance with UN Regulation 55.01 or later series of amendments, or
- approved and installed in accordance with the Norwegian Regulations of 5 July 2012 No. 817 on the Approval of Motor Vehicles and their Trailers (bilforskriften) or the Norwegian Regulations of 28 June 2022 on the Approval of Motor Vehicles and their Trailers (bilforskriften) cf. 1. and 2. above
(5) The trailer coupling(s) shall be deemed to have sufficient strength for use with the vehicle combination or modular vehicle combination in question if the calculated coupling forces based on actual masses do not exceed any of the characteristic performance values.
(6) Traceable calculations made using the calculator available on the Norwegian Public Roads Administration's website may be used as an alternative to the inspection authority performing the calculations in connection with a roadside inspection.