For a towbar box, your trailer coupling must have a minimum vertical load capacity (D-value or tongue load) sufficient for the weight of the box including the load, and it must be securely and correctly mounted. A fixed or detachable towbar suffices in most cases, provided that the maximum tongue loads of both the towbar and the vehicle are respected.

In addition, there are supplementary rules regarding lighting, license plates, and maximum speed that you, as the driver, must arrange yourself. In this article, we answer the most frequently asked questions about the requirements your trailer hitch must meet when driving with a tow bar case.

Which types of towbars are suitable for a towbar box?

A fixed towbar, a detachable towbar, and a swiveling towbar are all suitable for a towbar box, as long as the coupling has a standard ball size of 50 mm. This is the most common size in Europe and the size to which virtually all towbar boxes are mounted. The box clicks directly onto the ball coupling via a special mounting frame.

A fixed towbar is the simplest and most robust option. It is permanently attached to the car and requires no additional steps for installation. A detachable towbar offers the advantage that you can easily remove it when not in use, which enhances the appearance of the car. A swiveling towbar works in the same way but swivels away under the bumper.

What you must avoid is a tow bar with a non-standard ball size or a damaged coupling. A trunk that does not sit tightly on the ball can move and vibrate while driving, which is both dangerous and annoying. Also, always check that the tow bar has been correctly fitted by a certified installer and that the installation is documented in your vehicle's registration register.

What is the maximum load capacity of a trailer coupling for a towbar box?

The maximum load capacity for a towbar box is determined by the lower of two values: the maximum tongue load of the towbar itself and the maximum tongue load permitted by the car manufacturer for your vehicle. These values are listed in the car's registration book and in the towbar documentation. In practice, the permitted tongue load for passenger cars is typically between 50 and 100 kilograms.

A towbar box with contents can easily weigh 30 to 60 kilograms or more, depending on what you load into it. It is therefore essential that the total weight of the box, including cargo, never exceeds the permitted tongue load. Exceeding this limit can lead to damage to the towbar, the rear bumper, or the bodywork, and in that case, you will no longer be insured for any damage.

Furthermore, distribute the load as evenly as possible in the trunk. A trunk heavily loaded on one side can affect the stability of the car, particularly at higher speeds or when cornering. Heavy items should be placed as close as possible to the attachment point, and therefore as far forward in the trunk as possible.

Does a trailer coupling need to be TÜV-certified for a towbar box?

A trailer coupling does not need to be specifically TÜV-certified for use with a towbar box, but it must be officially approved and type-approved for your vehicle. In most European countries, including the Netherlands, a towbar must have type approval (E-marking) and be correctly registered in the vehicle's registration register.

A TÜV mark on the towbar itself is a quality indicator showing that the product has been independently tested for strength and safety, but it does not replace the legally required type approval. Therefore, always buy a towbar from a recognized supplier and have it installed by a certified company that also handles the administrative processing.

A similar reasoning applies to the towbar box itself. Choose a box that has been demonstrably tested for safety and quality. Our towbar boxes are developed and manufactured in the Netherlands and are subjected to rigorous quality tests, so you can hit the road with confidence.

What effect does a towbar box have on the rear lighting and license plate?

A towbar box must not wholly or partially cover the rear lights and the license plate of the vehicle. This is legally required in the Netherlands and applies in almost all European countries. If the box obscures the rear lights or the license plate, you are required to mount a lighting bar or license plate extension to the rear of the box.

Most high-quality towbar boxes come with, or are compatible with, a connectable light bar. This bar connects to the standard 7-pin or 13-pin socket of the towbar and ensures that taillights, brake lights, and turn signals remain visible to traffic behind you. Always check that all lights are functioning correctly before departure.

A license plate holder attached to the rear of the trunk must display the vehicle's original license plate number and must not deviate in size or readability. Some countries impose additional requirements regarding license plate lighting when using a trailer. Check these requirements if you are driving abroad to avoid fines.

What are the speed and loading regulations for driving with a towbar box?

In the Netherlands, the same maximum speeds apply to driving with a towbar box as to normal driving, provided that the total weight of the box, including the load, does not exceed the permitted tongue load and the box is correctly attached. There is no statutory speed reduction specifically for towbar boxes, but caution at high speeds always remains advisable due to the extra weight behind the car.

The following practical rules apply to the cargo:

• The weight of the suitcase, including contents, must not exceed the maximum tongue load of the towbar and vehicle.
• The load must be properly secured so that it cannot shift during driving.
• Heavy objects belong as close as possible to the attachment point, so at the front of the trunk.
• The case itself must be securely locked and must not be able to blow open during the journey.

Also bear in mind that a loaded cargo box affects your car's driving dynamics. The car responds more slowly to steering input and has a longer braking distance. Adjust your driving style accordingly, especially on the motorway and during emergency braking. Also check the tire pressure before departure, as an extra load at the rear can affect the load on the rear axle.

If you are driving through other European countries, the rules may vary by country. In Germany, France, and Italy, different regulations sometimes apply to trailers or protruding loads. Check the local traffic rules before crossing the border so that you do not encounter any surprises along the way.

Do you have any further questions about the right towbar box for your situation, or do you want to know which model best suits your car and travel needs? Contact us with our team or view the full range at vdlhapro.com.