Roof boxes expand the space to store things in the car when travelling and are convenient for carrying ski equipment. But what is important about roof boxes in terms of payload, speed and fuel consumption? A few tips from the experts will help to use them sensibly. Roof boxes usually require a base bracket that is adapted to each car model, which can only be mounted at the points provided for this purpose. This not only ensures a firm fit, according to the German certification firm Tüv Süd, but also prevents damage to the bodywork and paint. Attention to the maximum load supported by the roof Chests cannot withstand an infinitely heavy load. The amount that can be entered depends on the specifications of the box manufacturer and the maximum load allowed on the roof of the car. It is usually between 50 and 100 kilograms; a glance at the car manual will make it clear. An important fact to keep in mind is that you also have to calculate the weight of the box itself and the transport system. Not only does the roof trunk have to be secured from slipping, but you also have to securely accommodate the cargo inside, for example with tie down straps. Another option is to place a blanket or sleeping bag on the front of the chest to prevent delicate objects from skidding to the front during braking and being damaged by the impact. Experts recommend checking the attachment of the hood to the roof of the car after traveling the first 50 kilometers, and adjust it if necessary. Do not drive as fast as usual From a purely legal point of view, there is no special speed limit for cars that load a roof box. But, according to the German Automobile Club (ADAC), the roof box is considered a load, and the speed must be “reasonable”. Some manufacturers advise a certain maximum speed, which must be respected for liability issues. The ADAC recommends a maximum speed of 130 kilometers per hour. On the other hand, the car with a roof box reacts more sensitively to the side wind. Fuel consumption also increases. According to ADAC measurements, at a speed of 130 kilometers per hour, fuel consumption increases by 18 percent, that is, just under a liter more every 100 kilometers. For this reason it is best to remove the box as soon as possible after use. An important detail is that drivers should never forget the unusual height of the car with the roof box, because otherwise it can creak unpleasantly if you enter, for example, an underground car park with a low-rise entrance. dpa