Fundamentally, two main driving resistances prevent us from driving at infinite speeds: rolling resistance FRoll and aerodynamic drag FAir. These two forces act on a flat route in opposition to the vehicle's propulsion force, effectively braking the automobile.
Source: Wikipedia (https://bit.ly/2EVmSyR)
The effect of these mentioned resistances depends heavily on the speed being driven. At approximately 30 km/h, the influence of rolling resistance is about 90%, while aerodynamic drag accounts for only about 10%. Therefore, one could theoretically drive with a wall unit on the car roof without significantly increasing fuel consumption, provided the wall unit is lightweight.
At a speed of approximately 100 km/h, the influence of aerodynamic drag already reaches a remarkable 63%, and at 160 km/h, it is 81%. At even higher speeds, the vehicle's propulsion force practically only contends with aerodynamic drag.
Therefore, to develop a roof box that does not negatively impact vehicle performance even at high speeds, an aerodynamic shape is essential.
Downforce
Particularly sport-tuned vehicles generate downforce through their design. While this causes a minimal increase in fuel consumption, the force acting perpendicular to the road ensures enhanced cornering performance and increased safety. This is a factor that should not be underestimated, especially in modern, high-powered vehicles.
Fun Fact: At high speeds, a Formula 1 car generates so much downforce that if you were to turn the racetrack upside down, it would still "stick" to the asphalt.
So far, so good. In our implementation, we took Mother Nature as our model, because nature is the best advisor when it comes to efficiency. Over millions of years of evolution, nature has adapted perfectly to its environment. It is no coincidence that a penguin, shaped like a teardrop, possesses the perfect aerodynamic form. This insight has meanwhile also reached the engineering world!
Result
Our result is impressive: an optimized roof box, Made in Germany, without having to make compromises. Built from carbon fibers or CO2-neutral high-end natural fibers. Engineered to create a perfect symbiosis between car and roof box.
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The drag coefficient (Cd) of the ASPHALTKIND roof box is a mere 0.11 (water droplet level) and is thus approximately 30% lower than that of conventional roof boxes. At first, that may not sound like much. However, it must be noted that due to the geometric design, downforce is generated rather than lift, as is the case with conventional roof boxes (or even the extremely aerodynamic aircraft wing). Expressed in numbers, at a speed of 160 km/h, the roof box presses the vehicle vertically onto the road with approximately 110 N (approx. 10 kg). In comparison: a conventional roof box pulls the vehicle slightly upward. This results in reduced traction during highway driving and consequently poses an increased risk of accidents, especially on wet roads. Visually, the result can be represented as follows:
Conventional roof box with large wake area (black region)
Conventional roof boxes exhibit high turbulence intensity (turbulent = bad) in the rear section. This results in a large so-called wake area, which occupies about 1/3 of the roof box length before the streamlines converge again in a laminar fashion (laminar = good). Such turbulent effects negatively impact the performance of the roof box and cause increased fuel/energy consumption due to the negative pressure that forms.
ASPHALTKIND roof box with a significantly smaller wake area
With the ASPHALTKIND roof box, the aerodynamic teardrop shape leads to significantly lower flow separation in the rear section and thus also to a markedly reduced fuel/energy consumption. Overall, this results in a much more homogenous flow pattern with a pronounced laminar progression. Just almost like a penguin.
In general, of course: Only through perfect aerodynamics combined with high stability achieved by using carbon fiber is it possible to drive the (super) sports car uncompromisingly regarding speed on an exit, a road trip, or on the way to a vacation.