A vehicle's towing figure is quoted as a single number, but it is the result of several separate limits interacting. Understanding which limit binds first explains why the headline figure is often unusable.
Several ratings apply at once
Each vehicle carries a maximum for its own laden weight, a maximum for each axle individually, a maximum trailer weight, and a maximum for the vehicle and trailer combined.
All of these must be satisfied simultaneously. Meeting the towing figure while exceeding the combined figure is not permitted, and the combined limit is frequently the one that binds.
The numbers appear on a plate attached to the vehicle, and they refer to that specific vehicle as built rather than to the model in general.
Payload is what is left over
Payload is the difference between the vehicle's maximum laden weight and what it actually weighs empty, which means every option fitted reduces it.
A large sunroof, additional seats, a heavier trim level and four-wheel drive all consume payload before any passenger or luggage is added.
Two vehicles of the same model can therefore have materially different payload figures, which is why the plate matters more than the brochure.
The trailer pushes down as well as pulling back
A trailer applies a downward force at the coupling, and that force is part of the towing vehicle's payload rather than the trailer's weight.
Because the coupling sits behind the rear axle, it acts as a lever, adding more load to the rear axle than the nose weight itself and lifting weight off the front.
Weight lifted off the front axle reduces steering and braking authority, which is the mechanism behind the unstable feeling of a badly loaded combination.
Ratings are set by testing, not by engine output
Manufacturers determine towing figures through defined procedures covering hill starts on a specified gradient, cooling under sustained load, and stability at speed.
Cooling capacity is often the binding constraint rather than power, since a long climb at low speed generates heat with little airflow to remove it.
Brake performance with a trailer attached is assessed separately, and the presence of trailer brakes changes what the vehicle is permitted to pull substantially.
Why electric vehicles quote lower figures
An electric vehicle's own mass consumes a large part of its combined weight allowance before a trailer is attached, which compresses the towing figure.
Energy consumption while towing rises steeply because a trailer adds frontal area and drag, and range can fall by a large fraction on a motorway journey.
Charging with a trailer attached is a practical obstacle as well, since most charging bays are not laid out for a vehicle and trailer combination.