Fitting the box to the roof bars can be quite a chore in itself, depending on the height and width of the car and the type of fasteners supplied. Both the medium and large Thule boxes were the easiest to secure to the roof bars as they have intergrated clamps.
Five of the other boxes require U-bolts to be pushed around the bars from beneath the box and secured with nuts from the inside. Both the medium Rola and large Rhino boxes need two people to attach the box to the roof bars. The small Rola has four U-shaped hooks permanently fixed with nuts which had to be pushed in and straightened from inside the tray. This can be done with one person, but access is difficult.
The more difficult a box is to put on, the more likely you’ll leave it on permanently – not a good solution as this may increase fuel consumption. Fitting the boxes to the station wagon used for the test was already quite difficult, so those planning a box for a 4WD may need a ladder to help attach it to the roof.
Opening it up
An ideal situation when opening the box would be if it opened and locked from either side. Only the large Thule had this feature. The next best possible option would be to have the lid opening on the passenger side, away from traffic. The medium Rola and Thule had this type of lid. The small Rhino and Thule and the medium Rhino had the opening and lock on the rear; less than ideal for reach. Access and locks on the driver side only is the more dangerous option if you can’t pull off the street.
Filling it up
The boxes have to be loaded once they’ve been fixed to the car, and none of the boxes makes this particularly easy to do. The narrower the box, the further you have to reach to push your load in. That means lifting your piece of luggage up till it’s eye level with the edge of the box and sliding it in. It did help that the medium sized Rhino was considerably wider than the others and hence the side of the box was closer to the edge of the car. It may be simpler to mount the box to one side if the instructions allow for it.
Some boxes have straps for securing items. This can be useful since constant braking and accelerating can move around the contents inside the box, especially on long trips and when the box isn’t fully loaded. The small and medium Rhino and the medium Thule did not have any securing straps (but Thule has informed us that they now provide two straps with this box).
Our tester found that driving with a fully loaded car roof box changes the centre of gravity, and the car handles differently. This slightly affected cornering and braking. He found the same outcome with a double lane change (swerving out of one lane into another, and then back). While all fully laden boxes affect driving, the difference between the boxes was too marginal to score. The difference in noise was also too slight to score.
We tested fuel consumption by driving over 800km without a car roof box attached and then the return trip with the largest (empty) car roof box over the same stretch of road. The overall weight of the car was the same on both trips. We found that 11% more fuel was used when driving with the box. This is indicative and will vary depending on the car roof box and your speed.
None of the boxes allowed water to enter the inside during our rain test.
Installation The weight of the boxes in our test ranged from 8 to 19kg, but they are large. If you plan on lifting them onto a car, get some help to avoid any damage to yourself or the car. Securing them can be difficult due to the fixing mechanism and the height of the bars from ground level. Using a stepladder can mitigate some of the risk associated with installation. The height addition should also be taken into account when parking in a covered car park.
Auto carwash Most of the roof box manuals warn against putting the roof box through an automatic carwash.
Lock/lid location Look for a car roof box with access and locks on both the passenger and driver side, allowing easy retrieval of luggage whether stopped by the side of the road or at your final destination.
Loading/unloading Putting the heavier items in the boot of the car and the lighter items in the car roof box will make sure the centre of gravity is not changed too much and you don’t need to lift up the heavier items. If you have to put heavier items in the box, evenly distribute and secure them with straps if possible. If you have a slim box, or a wide car, the box will sit further away from the side of the car, making loading and retrieval of luggage more difficult. Look for a box that has smooth covers over the inside of the fastening mechanism. If the fasteners protrude into the box, take care not to pack anything over them that could be damaged.
Handling of car Our tests showed slight variations in handling when a fully laden box was attached to the car; the feeling of the extra weight did make a difference during cornering and emergency avoidance maneuver. You may find that you have to adapt your driving to compensate for these differences.