Choosing a roof box: size, roof load, mounting and opening

How many litres do you need?

The volume is in litres in the product name. For the Thule roof boxes in our catalogue it runs from 300 litres for the Force 3 S, through 400 litres for the Force 3 M and 500 litres for the Force 3 XL, to 590 litres for the Motion 3 XXL. Hapro gives 370 litres for the Traxer 5.6 and Farad 680 litres for the Marlin N7.

Litres are only half the story: length and width decide what fits. Long items such as skis need a long box; Thule says roof boxes suit skis up to 215 cm. According to Thule a narrow sport box leaves room on the roof beside it for a bike or kayak. Put soft, bulky things such as sleeping bags, clothes or skis in the box and keep heavy items inside the car.

Length and the tailgate

A box does not make the car longer, but it must not get in the way of the tailgate. Thule advises checking the car's roof dimensions and roof load before buying, so the box fits and the boot can open fully. Do it with the box fitted: open the tailgate all the way and see whether it touches the box. A shorter box or another position on the bars often gives the room.

Mind the height too: according to Thule the vehicle can become up to 70 cm taller with rack and box. Watch for low garage entrances and low branches. In an automatic car wash the box and rack must be removed.

Roof load: how much can go in?

There are three limits: the car's roof load (in its manual), what the roof rack can take and the box's own maximum load. The Thule roof boxes in our catalogue have "75 kg" in their names.

Thule describes the roof load in use as the weight of the roof rack plus the weight of the roof box plus the weight of the payload. The vehicle manufacturer's instructions on the maximum roof load must be followed. So: the roof load from the car, minus the roof bars, minus the empty box, is what you may load. The car's permissible total weight must not be exceeded either. Plan with the dynamic roof load, which applies while driving.

Thule's advice is to spread the load as a quarter, a half, a quarter: about half the weight in the middle between the bars, a quarter at the front and a quarter at the back. Nothing may be attached to the outside of the box.

Opening: one side or both

The Thule boxes in our catalogue ("Motion 3", "Force 3", "Pulse 2") have "opens on 2 sides" in their names. A box that opens on both sides can be loaded from the kerb as well as from the road side, handy when you park at the roadside or close to another car. For other models the product description says whether they open on one or both sides.

Mounting and roof bars

A roof box needs crossbars on the roof (roof bars). Most boxes have a universal mount; some racks need an adapter, for example racks with a T-track, for which there is the Hapro Premium Master Fit T-track adapter. Whether the box fits your rack is in the box's instructions; Thule has its own car fit finder.

Thule's safety instructions give these rules:

• Mount the box only on approved rack systems, preferably tested ones (for example GS-tested) that are approved for your vehicle. Mounting on towbar carriers is not permitted.
• The front faces the driving direction and the box sits as parallel to the road as possible, to avoid extra lift.
• If the instructions give no special position, keep at least 700 mm between the crossbars.

Speed, lock and storage

Speed: According to Thule's safety instructions your speed must always suit the load, the road and the wind, and must under no circumstances exceed 130 km/h. Speed limits still apply. Expect wind noise and different handling in crosswinds, in bends and when braking.

Lock: Close and lock the box before you drive off and take the key out. If the box has not been used for a long time, check the locks, the load and the fixing. Thule recommends noting the key number so you can order a replacement quickly if you lose it.

Storage: Thule recommends removing the box and rack when not in use, for fuel economy and out of consideration for other road users. Store the box dry and out of direct sunlight. A roof box cover protects it in storage.

Comparing prices

Under roof boxes you find all models with prices from several shops. Each size and version has its own EAN and Sorppa compares them one by one, so you see prices for exactly the same box.