It's confusing.... From my understanding a BE licence means you can tow 3500kg.
Say an E39 530D has a towing capacity of 2000kg.
So you have a transporter with a gross weight of 2000kg, trailer itself weighs 400kg that means the car on it must be under 1600kg.
I think Falcon on here used to tow his E36 tracl car with his E39?