Weights, nose weight and towing limits

By the end of this topic you can

• You can explain maximum authorised mass (MAM), unladen weight and gross train weight.
• You can find your car's weight limits on its manufacturer's plate or in the handbook.
• You can state the weight limit for a trailer without brakes.
• You can load a trailer so the nose weight is within limits and the load is even.
• You can state the maximum width and length of a trailer towed by a car.

What you need to know and understand

• MAM is the weight of a vehicle or trailer including the maximum load it can safely carry.
• Unladen weight is the weight of a vehicle when it is not carrying passengers, goods or other items.
• Gross train weight is the maximum weight of the vehicle and trailer together, and must not be exceeded.
• A loaded trailer without brakes must not weigh more than 750kg, and should not weigh more than 50% of the car's weight.
• A trailer must have working brakes if it weighs over 750kg when loaded.
• The maximum trailer width for any towing vehicle is 2.55 metres.
• A vehicle with a MAM of 3,500kg or less cannot tow a trailer longer than 7 metres.
• Nose weight is the downward load the trailer puts on the tow ball, and the manufacturer's limit must not be exceeded.

Reading the manufacturer's plate

Most cars have a plate, often on the door pillar or under the bonnet, showing up to four weights. The handbook gives them if there is no plate.

Remember the maximum weights include passengers, luggage in the car and fuel, so a full family car has less margin than an empty one.

1. Weight 1: the maximum weight of the car on its own.
2. Weight 2: the maximum weight of the car and trailer together (gross train weight).
3. Weight 3: the maximum weight on the front axle.
4. Weight 4: the maximum weight on the rear axle.

Braked and unbraked trailers

Small trailers often have no brakes of their own. Loaded, such a trailer must not weigh more than 750kg, and should not weigh more than half the weight of the car. With a braked trailer, the car and loaded trailer together must not weigh more than the second weight on the car's plate.

Your car's handbook also lists separate maximum towing weights for braked and unbraked trailers. Check both, together with your licence limit, and tow within the lowest.

Nose weight and loading

Nose weight, also called tow ball load, is how hard the front of the trailer presses down on the tow ball. Too little can make the trailer unstable and prone to snaking. Too much overloads the car's rear and the tow bar. The car and tow bar makers give a maximum figure, and the Highway Code says it should not be exceeded.

You can measure nose weight with a simple nose weight gauge under the hitch. Adjust it by moving the load forward or back.

• Put heavy items low down and over the trailer's axle or axles.
• Spread the load evenly from side to side.
• Make sure there is a downward load on the tow ball.
• Tie everything down so nothing can shift or stick out dangerously.

Size limits and why they matter

A trailer towed by any vehicle must not be wider than 2.55 metres. If your car's MAM is 3,500kg or less, the trailer cannot be longer than 7 metres. A wide or long trailer also needs proper towing mirrors and more care on narrow roads, and you should watch for weight, width and height restriction signs on your route.

Common mistakes

• Guessing the trailer's weight. Use a public weighbridge or check the load against the trailer's plated MAM.
• Loading heavy items at the very back of the trailer. This reduces nose weight and can cause snaking.
• Forgetting that people and luggage in the car count towards the gross train weight.
• Overfilling a small unbraked trailer past 750kg.
• Not re-checking nose weight after changing the load for the return trip.

Test yourself: Weights, nose weight and towing limits

Answer each question, then read the explanation. Questions come in a random order each time.

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