How to Use This Tool
Fill in the plate figures from the door jamb and the weight of the loaded trailer. All four limits are checked together, because they bind independently.
The four limits
- GVWR — the most the vehicle may weigh fully loaded, including passengers, cargo and tongue weight. Payload is GVWR minus kerb weight.
- Towing capacity — the most the trailer may weigh. The advertised headline number, usually quoted for a bare vehicle with one driver.
- GCWR — the most the vehicle and trailer may weigh together. This is often what stops you loading both to their individual maximums.
- Tongue weight — the downward load on the hitch, which must be within a range, not merely below a maximum.
You have to be inside all four at once. Passing three does not help.
Tongue weight is payload
This is the part that catches people. The trailer's nose presses down on the hitch, and that force is carried by the vehicle. So it counts against payload — the same allowance as passengers and luggage — not against towing capacity.
Work through the example: a 3,175 kg GVWR truck weighing 2,400 kg empty has 775 kg of payload. Four adults take 320. A 2,000 kg trailer with 12% on the tongue takes another 240. That leaves 215 kg for everything else, in a truck rated to tow 3,000 kg.
Adding another 500 kg to the trailer would add 60 kg of tongue weight, which comes out of the same 215. The trailer would still be inside the towing rating; the truck would be running out of payload.
Why too little tongue weight is worse than too much
Below roughly 10%, a trailer can begin to sway from side to side, and the motion feeds itself: each oscillation pushes harder on the tow vehicle, which pushes back, and the amplitude builds. It typically appears at speed, on a downhill, or when a lorry passes — and braking hard usually makes it worse.
Too much tongue weight is also bad, but it fails gently: the rear axle takes more than its share, the front end lifts, and steering and braking go vague. You notice it, which is a meaningful difference.
10–15% is the conventional range for a conventional hitch. Fifth-wheel and gooseneck couplings sit over the rear axle and use 15–25%, which is one reason they are more stable.
Loading fixes it: move weight forward of the trailer axle to increase tongue weight, backwards to reduce it. Small movements matter, because leverage about the axle is what sets the number.
Weigh it rather than estimating it
Every figure entered here is a guess unless it came from a weighbridge. Kerb weight from a brochure excludes options, a full tank, roof bars and everything living in the boot; the same model can be a hundred kilograms apart in the real world.
A public weighbridge is inexpensive. Weigh the vehicle loaded as you will drive it, then again with the trailer coupled, and the difference at the rear axle gives real tongue weight. That is the only version of these numbers worth trusting.
Legal limits, licence categories and speed restrictions for towing vary by country and by licence date. This is arithmetic against the numbers you typed, not legal advice.
