Gross train weight is the most the loaded car and the loaded trailer may weigh together. It is usually the second figure on the car’s VIN plate. GOV.UK says it "must not be exceeded", and if the plate has no train weight, the car should not tow.
How it limits the trailer
Take the gross train weight and subtract what the car actually weighs loaded, with people, luggage, fuel and the noseweight. What is left is the most the trailer can weigh (GOV.UK). In Ireland the RSA calls the same figure the design gross combination weight (RSA).
Example: a car with a 3,950 kg train weight, loaded to 2,150 kg, leaves 1,800 kg for the trailer. Load the car to its full MAM and that figure is what you have. Towsheet uses the full MAM when you don't give a loaded weight, which is the cautious answer.
Not the same as the towing limit
The braked towing limit is a separate figure in the handbook. Both apply: the trailer must be within the towing limit, and car plus trailer within the train weight. On many cars the towing limit is lower; on some heavily loaded cars the train weight binds first.
Not a licence weight
Licence rules use the plated MAM of the car and trailer, not the train weight and not the actual weights. A legal outfit has to pass both tests.
Questions
- Where is the gross train weight?
- Usually the second weight on the car manufacturer’s plate (VIN plate), often inside the driver’s door or under the bonnet.
- What if my VIN plate has no train weight?
- GOV.UK says that if the VIN plate does not list a train weight, you should not use the vehicle for towing.
Sources
- Gross train weight must not be exceeded: GOV.UK, Towing with a car, checked 3 November 2026.
- Ireland: design gross combination weight: RSA, Towing and vehicle towing capacity, checked 3 November 2026.
- The car’s braked and unbraked towing limits: GOV.UK, Tow a trailer with a car: safety checks, checked 3 November 2026.
Guidance, not legal advice. Towsheet is independent and not connected with the DVLA, DVA, RSA or NDLS.