If your trailer has a maximum authorised mass (MAM) of 3,500 kg, it means the trailer plus everything loaded into it must not weigh more than 3,500 kg when used on the road.

What “maximum authorised mass” means

  • MAM is the legal maximum weight of the trailer including its load, as set by the manufacturer and recognised in law.
  • This figure is usually shown on a plate or sticker on the trailer chassis or body and in the documentation.
  • It is not the empty weight of the trailer, and it is not “how much cargo you can add” on top of 3,500 kg – it’s the total allowed when loaded.

So, if your trailer’s MAM is 3,500 kg and the empty trailer weighs, for example, 900 kg, your maximum legal payload is 2,600 kg (3,500 – 900). Exceeding that makes the trailer overweight, even if it “feels fine” to tow.

Why 3,500 kg matters

  • 3,500 kg is a key legal threshold in UK and EU-style regulations for both vehicle categories and driving licence entitlements.
  • Above certain MAM limits, different licence categories, testing, and sometimes tachograph or operator licensing rules can apply, especially for commercial use.
  • Exceeding MAM or overall combinations (like gross train weight) can lead to fines, points, and potentially court if the excess is dangerous.

In other words, “maximum authorised mass of 3,500 kg” is the legal ceiling for that trailer when loaded, and you must also ensure that:

  • Your tow vehicle is approved to tow that weight.
  • The combination of car + trailer + load does not exceed the car’s own limits (like gross train weight).

Think of MAM as the trailer’s “do not exceed” line on a measuring jug: the total of trailer plus cargo must stay at or below 3,500 kg.