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Safety and breakdowns , On the road , Know your car · Updated 2026-10-18

Towing and roof loads: the basics

Many people tow a caravan, a small trailer or a boat, or put a roof box or bikes on the car for the holidays. These things change how the car accelerates, brakes and handles. The limits that matter are set by the car maker, and the rules about licences, speed and equipment differ by country, so check with the competent authority before you tow.

Know your limits

Every car has weight limits. You can find several of them in the owner's manual and in the registration documents; see understanding the data plate for the plate under the bonnet or in the door frame. The key terms are:

• Kerb weight: the weight of the empty car, with fluids but no passengers or luggage.
• Payload: how much you can carry (people, luggage, roof box) on top of that.
• Maximum permitted weight: the most the loaded car may weigh.
• Towing capacity: the maximum weight of a trailer the car may pull, often given separately for braked and unbraked trailers.
• Nose weight (tow ball load): the downward force the trailer puts on the tow ball.
• Roof load limit: the maximum weight allowed on the roof, which is usually much lower than people expect and includes the box or rack itself.

Never exceed any of these. If the manual and the plate disagree, use the lower figure or ask the maker or a workshop.

Roof boxes and racks

A roof box or rack is the easiest way to add space, but it changes the car in several ways:

• It raises the centre of gravity, so the car leans more in bends and is more affected by crosswind.
• It adds air resistance, so fuel use goes up, especially at motorway speed.
• It adds noise and can make the car taller than a garage or a car park barrier.

Use rails or bars approved for your car, fit them exactly as the instructions say, and check that they are tight before every trip and after the first few kilometres. Put heavier items low and in the middle of the box, and lighter bulky items on top. Spread the load evenly and keep it within the limit. Remove the box when you do not need it; see how to save fuel. Drive more gently and slower than usual, and remember the extra height.

Bike carriers

Carriers on the tow ball or on the boot need to be secure, and they can hide the number plate or lights. Rules differ by country on what you must show, so check them. Make sure the bikes do not wobble or touch the car, strap the wheels and frames well, and check again during the trip. Bikes on the roof add height and drag, and tail-mounted bikes can make reversing and parking harder.

Loading the car inside

Weight inside the car matters too. Put heavy items low, as far forward as possible and close to the rear seat, and secure them so they cannot fly forward in a hard stop. Keep the cargo area clear of loose objects. If the manual recommends a higher tyre pressure for a full load, set it before you leave; see tyre pressure and rotation.

Towing a trailer

Towing is a skill worth practising in an empty car park before the first trip. Key points:

• Check that the car is approved for towing and has a suitable tow bar, fitted properly and with a working electrical connection.
• Load the trailer so that the nose weight is within the allowed range. Too little nose weight can make the trailer sway; too much overloads the rear of the car.
• Check the trailer tyres, lights, brakes and coupling before each trip, and check that the safety cable or breakaway cable is attached.
• Allow longer braking distances, drive slower, and take wider turns because the trailer cuts corners.
• Be careful of crosswinds and of being overtaken by large vehicles.

If the trailer starts to sway

A swaying trailer is frightening. Do not brake hard and do not steer against the sway. Ease off the accelerator gently, hold the wheel straight and let the speed fall. Once the car is stable, stop and check the load. Prevention is better: keep a moderate speed, balance the load and keep the nose weight right.

Insurance and paperwork

Ask your insurer whether towing and roof loads are covered, and what documents you need to carry for a trailer. Rules about licence categories, trailer registration and inspection differ by country. Check them with the competent authority well before the trip. For more on cover, see insurance types explained.

What to remember

• Find the weight limits for your car and never exceed them.
• Roof loads have a low limit that includes the box or rack.
• Secure everything and recheck it during the trip.
• Load heavy items low and keep the nose weight within the allowed range.
• Drive more slowly and brake earlier with a trailer or a roof load.
• Check local rules and your insurance before towing.

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