100 km/h approval for trailers: the key rules

Anyone who regularly visits large communities such as the Anhängerforum will be familiar with the phenomenon: questions about Germany's 100 km/h approval for trailers appear almost every day. At first glance, the regulations can seem complicated, and there is plenty of misinformation about which components actually have to be retrofitted to the trailer.

In this guide from trailer.one, we provide a factual summary of the legal requirements. We explain which technical requirements your trailer must meet and what role wheel shock absorbers and anti-snake couplings actually play.

The basic requirements: Tyres and brakes

Regardless of how heavy your towing vehicle is, your trailer must meet certain basic technical standards to qualify for Germany's 100 km/h approval (under the 9th Exemption Regulation to the German Road Traffic Regulations):

• Tyre age: The trailer tyres must be no more than six years old. The relevant date is determined by the DOT code on the tyre sidewall.
• Speed rating: The tyres must be approved for speeds of at least 120 km/h. This corresponds to speed rating "L" (or higher).
• Brakes: A trailer without its own braking system (e.g. a typical 750 kg trailer) may also qualify for the 100 km/h rule under certain conditions, although the requirements for the towing vehicle are considerably higher.

The mass factor: The towing vehicle makes the difference

One of the biggest misconceptions is that a trailer automatically has a general "100 km/h approval". The sticker on the rear merely indicates that the trailer is technically suitable. Whether you are actually permitted to drive at 100 km/h depends on the unladen weight of your current towing vehicle.

This is where the so-called mass factor comes into play. The trailer's maximum authorised mass must not exceed a certain value calculated on the basis of the car's unladen weight:

• Factor 0.3 (unbraked trailers): The car's unladen weight must be very high. Example: For a 750 kg trailer, the towing vehicle must have an unladen weight of at least 2,500 kg. Fitting wheel shock absorbers to the trailer does not change this factor.
• Factor 1.1 (braked trailers with wheel shock absorbers): This is where it becomes relevant for most users. If the trailer is braked and fitted with wheel shock absorbers, its maximum authorised mass may be up to 1.1 times the unladen weight of the car.
• Factor 1.2 (braked trailers with an anti-snake coupling): If you additionally equip your trailer with an anti-snake coupling (e.g. from AL-KO or Winterhoff), the factor increases to 1.2. Alternatively, this factor also applies if the towing vehicle is equipped with a dedicated ESP system featuring trailer stabilisation.

Retrofitting wheel shock absorbers: Is it worth it?

For most owners of braked trailers, the answer is yes. Without wheel shock absorbers, a factor of only 0.3 applies to braked trailers (the same as for unbraked models). Only by retrofitting shock absorbers does the factor increase to 1.1.

Retrofitting is straightforward on almost all common axles (such as AL-KO, Knott, Schlegl or WAP). Manufacturers usually provide the necessary mounting points on the suspension arms at