Towing, roof boxes and bikes: what they do to your EV’s range

Extra weight inside an EV usually has a relatively modest effect on its range. Anything attached to the outside can have a much larger impact, because it changes the car’s aerodynamics. A rear-mounted bike rack is generally more efficient than carrying bikes on the roof, while a large caravan can reduce your usual range by around half.

That does not mean electric family holidays or caravan trips are a bad idea. It does mean you should check the car’s weight limits, calculate with a realistic range and think about where you will charge, especially if you need to unhitch a trailer first.

It seems logical that filling an EV with people and luggage would drastically reduce its range. After all, the motor has to move more weight, right? In reality, the effect is often fairly modest. Weight matters most when you accelerate, climb hills or repeatedly slow down and speed up. Once the car is moving steadily on a flat road, the additional effort becomes smaller. EVs can also recover some energy while slowing down through regenerative braking.

In one test, German motoring organisation ADAC added 280 kilograms to an electric car and found that energy consumption increased by around 6%. The exact effect will vary by car, route and driving style, but the result offers some reassurance: your passengers do not need to choose between themselves and their second pair of hiking shoes.

That said, every car has a maximum payload. This is the total weight it can carry in addition to the car itself: passengers, luggage, accessories and, when towing, the downward pressure that the trailer puts on the towbar. Four adults, several bags and a couple of electric bikes can add up quickly. Different versions of the same model may have different weight limits, so check the specifications for the exact car you are driving.

A roof box does not only add weight. It changes the shape of a car that has been carefully designed to move through the air with as little resistance as possible. The same applies to bicycles, roof tents and caravans. The faster you drive, the more energy the car needs to push these objects through the air. This is why an item attached to the outside can affect range far more than the same weight stored inside the car.

ADAC tested an EV with different accessories at an average speed of 120 km/h. Two bicycles on a rear-mounted rack increased consumption by around 8%, while carrying the same bikes on the roof increased it by 25%. In other words, your EV is less concerned about the weight of the bicycles than about being asked to wear them as a hat. A roof box will also reduce efficiency, although the precise effect depends on its size, shape, position and your speed. Choose the most aerodynamic option available, mount it correctly and remove it when you no longer need it. Driving around all year with an empty roof box is a strangely expensive way to store air.

Then there is the caravan. A caravan combines extra weight with a large frontal area. It therefore increases both rolling resistance and aerodynamic drag, particularly at motorway speeds. During a test journey through four European countries, ADAC towed a fully loaded caravan with a Kia EV6. Average consumption rose from approximately 20 to 36.6 kWh per 100 kilometres, while the estimated range fell from almost 400 to around 220 kilometres.

Another ADAC test showed how much speed matters. With the particular car-and-caravan combination tested, the caravan increased consumption by 54% at 80 km/h, 79% at 90 km/h and 103% at 100 km/h. These are test results, not figures that apply to every combination. A smaller, lighter or more aerodynamic trailer may have a much smaller effect. Weather, terrain and driving style matter too. Still, planning for roughly half your usual range is a sensible starting point when towing a large caravan for the first time. It also makes slowing down one of the easiest ways to travel further.

Having enough power to move a caravan is not the same as being approved to tow one. Some EVs cannot tow at all, while others can pull anything from a small utility trailer to a large caravan. Different motor, battery and drivetrain versions of the same model may also have different limits. Before buying or hitching anything, check four figures:

• Towing capacity: the maximum permitted weight of the trailer. Cars usually have separate limits for braked and unbraked trailers.
• Nose or tongue weight: the maximum downward force the trailer may place on the towbar.
• Payload: the weight the car can carry, including people, luggage, accessories and nose weight.
• Gross combination weight: the maximum permitted weight of the loaded car and loaded trailer together.

These terms can vary slightly between countries, and so can driving-licence requirements, speed limits and other towing rules. The safest source is the official documentation for the exact car and trailer, combined with the rules in every country you plan to visit.

Remember that the listed weight of an empty caravan is not its holiday weight. Water, gas bottles, food, an awning, camping furniture and the impressive collection of objects that permanently lives in the cupboards all count.

The towing itself can be wonderfully smooth in an EV. Electric motors deliver power instantly, without gear changes or the sound of an engine wondering what you have done to it. But charging with a trailer… that’s often the less elegant part.

Many charging stations use conventional parking bays, with the charger positioned at the front or side. A car with a caravan may block the access road or several other chargers. The cable may not reach, and reversing into the space can be impossible. During its caravan journey, ADAC found that the caravan usually had to be unhitched and parked separately before the car could charge. Pull-through chargers (where the entire combination can stop alongside the charger without unhitching) make life much easier, but they are not yet available everywhere.

Before travelling, look at recent photographs or layout information for charging locations rather than checking only whether a charger exists. Larger charging hubs are more likely to offer space, but always make sure to have an alternative within range. A charger can be functioning perfectly and still be almost useless when approached with six metres of caravan behind you.

For occasional holidays with a full boot, a roof box or bikes on the back, the extra energy use is unlikely to make an EV impractical. Even towing can work well if the car has sufficient capacity and you are comfortable with a shorter range and more frequent charging stops.

The calculation changes if you regularly tow a large caravan over long distances. Suitable EVs need enough towing capacity, payload, range and charging speed and those models may be larger and more expensive than you otherwise need.

In that case, an EV may not be the most practical choice yet. You might be better served by a different type of car, or by driving an EV day to day and renting a tow car for the occasional demanding trip. There is little environmental sense in buying far more car and battery than you need all year because you tow a caravan for two weeks every summer. Your EV probably does not mind the overpacked boot. It is the bicycles on its head and the small house behind it that complicate matters.