We have been testing different roof boxes for over a year. We weren't very satisfied with any of them because, while individual features were good, the overall system could have been improved.
Our focus has always been on a lightweight design that allows speeds above 130 km/h and provides a comfortable level of wind noise.
We had already published a few blog posts on this topic, but they have since been archived. Nevertheless, we’d like to give you an idea of the results in this short post and raise your awareness of this topic to save you a lot of research.
It looks different in photos than it does in real life
The first thing we noticed were all the photos and illustrations we edited to make the roof box blend in as seamlessly as possible with the cars. That way, the boxes always look really good—until you see them on your own car, which may not have been modified.
Roof Box Design vs. Automotive Design
Most roof boxes are created by designers who choose to deviate from current automotive design trends or who are unfamiliar with automotive design.
As a result, many boxes feature sharply defined beading and edges, which were last seen in automotive design in the early 2000s.
At this time, we believe a clean and uncluttered design is more appropriate. No tunnels, beading, edges, spoilers, etc.
The clean design is (based on our own experience during development) much more challenging, because every line has to fit.
Basically, a roof box shouldn't look like a strange object on the car. It's not that easy, but it's possible!
Proximity to the car
As mentioned earlier, boxes in photos always appear to be very close to the car. It just looks sportier. If they’re that close in reality, this can actually be a problem. We’ve always wanted our boxes to be as close to the car as possible and have tested various base models. Visually, it does indeed look sportier. But it has two major drawbacks: the box hits the car’s roof when it’s loaded or “swings” when it’s empty. That causes many small scratches.
The box is too close to the car, which causes scratches and reduces aerodynamic performance
Another problem we’ve encountered is aerodynamic: air accumulates in front of the pit, and not enough wind flows under it. This becomes noticeable the moment you don’t have a rear wiper and have to rely on the wind. This could be managed if the rear spoiler or the car’s own aerodynamics weren’t there: If there’s no wind at the rear of the car, the cars experience aerodynamic problems related to downforce.
During a phone call with a development engineer at Porsche, we received confirmation that this is one of the reasons why we have to ensure that there is always enough airflow between the box and the car. Performance comes before design.
With our concept, we were able to solve the problem. We adopted a “conscious line management” approach “far away from the car” in order to ensure perfect aerodynamics while maintaining an excellent design for both the car and the pit box.
Roof boxes are to be opened
It sounds a bit silly, but one of the key features of roof boxes doesn’t work very often these days: smooth opening and closing. You often have to insert the small key into the keyhole first. After that, most models require quite a bit of effort to move the inner rail, which made us worried about putting luggage in the roof box during a winter trip, because the risk of breaking the key was too high for us.
Aside from that, once it’s unlocked, the biggest problem we face with almost every roof box is opening the top half. Depending on the material and construction, the top half starts to warp. The hinges, which allow it to be opened from both sides, seem to be overloaded, and basically everything is just very wobbly.
For us, a roof box should open as easily as a trunk lid.
The background noise
Admittedly, the Porsche 911 chassis and the insulation—which has been kept to a minimum in terms of weight—expose almost any noise from items in or around the car.
The same is true for roof boxes. Nearly all of them were very loud at low speeds and produced a lot of wind noise on the highway.
This would be acceptable for a low-budget product. But we have tested more expensive boxes, and we think there is definitely room for improvement.
The weight should not be underestimated
The weight of a roof box is often the first thing people compare. This is also very important for the following reasons:
- you can load more
- The standard roof load capacity is 75 kg, and if the box and the carrier's base already weigh 35 kg, then there is less room for your luggage.
For some models, you'll need a roof box lift or several people (image source: ATU)
- The standard roof load capacity is 75 kg, and if the box and the carrier's base already weigh 35 kg, then there is less room for your luggage.
- the car's high center of gravity is reduced
- While you're carrying your luggage in the box, the center of gravity is negligible, but you often use an empty box and appreciate having a lightweight box on the car
- The total weight of the car is reduced by using a light box
- Anyone who wants to save gas or energy, enjoys the car's dynamic performance, and would also like to be able to stop sooner when braking pays close attention to a lightweight car.
- The installation and removal of the box are often underestimated
- Sometimes you had to carry an empty box on your car because you couldn't remove the roof box by yourself.
The Speed
What speed can you reach while driving with a roof box on top?! Exactly. 130 km/h. The manufacturer always recommends a speed limit of 130 km/h, in case something happens to you while speeding with your roof box. That way, the manufacturer can avoid any liability for this.
However, the topic was also important for a second reason: A 911 owner simply doesn't want to drive at 130 km/h all the time.
A comfortable speed that can be reached on the highway is 170 km/h. This was the feedback we received from BMW, Audi, Mercedes, and Volkswagen owners in response to our inquiries: “We want to speed up when traffic conditions allow it.”
While a general speed limit for Germany has been mentioned before, the main idea here is “If I wanted to, I could.” Just like driving a car in general, the feeling that you can actually go wherever you want isn’t limited by speed. Just as in Switzerland, where sports cars are sold even though there are strict speed limits, roof boxes shouldn’t restrict your car too much and should, at least in part, reflect the idea of freedom.
We received a relevant comment in response to a post on our blog that sums up the experience of driving with a standard roof box: “The moment I put a roof box on my car, my Audi A6 turns into a truck. It’s slow, aerodynamically inefficient, unstable, and ugly. Even the fact that I can’t go faster than 130 km/h bothers me.”
By the way, a top speed of up to 300 km/h—as was achieved with a carbon-fiber prototype—is actually possible. This, however, comes at the expense of the vehicle's overall weight, since stability and weight are often at odds with one another.
A good combination is important to us. Our focus isn’t on driving 300 km/h with our roof box. Rather, it should be able to withstand a lap on the Nordschleife, where, among other things, high (lateral) dynamic forces are required due to sharp, fast curves and intense acceleration and braking. You could test the box’s high-speed performance on the Döttinger Höhe (long straight).
To sum up
To be honest, we tested absolutely everything, and we’re completely open to all manufacturers and their promises. But no one ever really convinced us. Our philosophy is this: If there’s a problem, you have to find a solution. That’s why we accepted the challenge and are now working on the perfect roof box for all of you. After all, the ones that are already available aren’t bad at all, but things get even better if you don’t have to make any compromises.