On second-hand sites and among specialists, the volumes of roof boxes generally range from 315 to 650 litres. To find the right one for you, you can take into account the size of your car, but especially what you want to transport:
> Long objects (skis, surfing…): you need a long roof box.
> bulky objects (stroller, crib): a mixed chest may be sufficient. (Feel free to go to the store to take the test).
Long roof box and small car, is that possible?
> In theory, if the spacing of the roof bars allows it, it is always possible to put a long roof box on a small vehicle. On the other hand, you will have loud wind tunnel noises if the trunk protrudes to the front of the pavilion. Very unpleasant on long journeys!
> The short trunks (volume from 315 to 370 litres) are suitable for urban and small family cars.
> As for mixed safes, they are the most popular. Thanks to their larger widths, they have capacities ranging from 340 to 480 litres, and are suitable for all types of cars, station wagons, 4x4s and sedans.
Is a roof box noisy and energy consuming?
The boxes are resistant to air, causing more or less significant disturbances. Less high, more aerodynamic and equipped with diffusers (such as racing cars), the profiled trunks are the quietest.
Air resistance affects your consumption (+15% depending on your speed). An effect that you can always limit, on the one hand by favouring a model that is as close as possible to your needs in terms of bedding, and on the other hand by reducing your speed.
How to distribute the loads between vehicle and roof box?
> Remember that you can generally load a maximum of 85 kg in your roof box and that you should also always check the load capacity of the roof bars.
> Instead, fill it with light but bulky objects and reserve the space available in the vehicle for heavy objects.
> Place the heaviest objects at the bottom, near the roof racks that carry them.
> Inside the trunk, always attach your load with straps or a net to avoid very unpleasant mass transfers when cornering and braking.
How to decide between the different opening and closing systems?
> Centralized lock: by closing a single lock, two locks are activated simultaneously at different locations in the trunk for increased security (Multi-point lock principle).
> Secure lock: keys cannot be removed if the trunk is open. It is therefore impossible to leave the trunk unlocked, or to forget your keys in the trunk.
> Bilateral opening: the trunk opens on both sides, which is particularly convenient in town to always load or unload on the sidewalk side.
> Power-assisted opening: less effort to open the trunk on the roof, which always stays open while you load it.
What does the litering of my roof box correspond to?
300 litres, 600 litres... It is not always easy to imagine what such large volumes correspond to.
In general, we can consider:
A large travel bag = 100 litres
One large suitcase = 200 litres
A trunk of 206 (without folding the bench) = 245 litres
A refrigerator (and its freezer part) = between 250 and 300 litres
But beware, roof boxes are (fortunately) not cubes. It will therefore be much easier to place flexible bags than large rigid suitcases.