Basically, two major types of rolling resistance prevent us from driving at infinite speeds: rolling resistance FRoll and air resistanceFLuft. These two forces act against the driving force of the vehicle on a flat road and literally slow the car down.
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The effect of these resistances depends heavily on the speed at which you are traveling. If you are traveling at approx. 30 km/h, rolling resistance accounts for approx. 90% of the total resistance and air resistance only approx. 10%. This means that you could drive with a wall unit on the roof of your car and your fuel consumption would not be significantly higher, provided that the wall unit is lightweight.
At a speed of approx. 100 km/h, the influence of air resistance is already a considerable 63%, and at 160 km/h it is already 81%. At even higher speeds, the vehicle's driving force is practically only fighting against air resistance.
In order to develop a roof box that does not negatively impact the vehicle's performance even at high speeds, an aerodynamic shape is essential.
contact pressure
Sporty vehicles in particular generate downforce due to their design. Although this causes fuel consumption to rise slightly, the force acting perpendicular to the road improves performance in corners and increases safety. This is a factor that should not be underestimated, especially in modern vehicles with more powerful engines.
Fun fact: At high speeds, a Formula 1 car generates so much downforce that if you turned the race track upside down, it would still "stick" to the asphalt.
So far, so good. When it came to implementation, we took Mother Nature as our role model, because nature is the best guide 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, with its teardrop shape, has the perfect aerodynamic form. Incidentally, this insight has also found its way into the world of engineering!
result
The result is impressive: an optimized roof box, made in Germany, without having to compromise. Constructed from carbon fiber or CO2-neutral high-end natural fibers. Developed to create a perfect symbiosis between car and roof box.
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The Cw value of the ASPHALTKIND roof box is just 0.11 (water drop level), which is approximately 30% lower than that of conventional roof boxes. That may not sound like much at first. However, it should be noted that the geometric design generates downforce rather than lift, as is the case with conventional roof boxes (or even extremely aerodynamic aircraft wings). In figures, at a speed of 160 km/h, the roof box presses the vehicle vertically onto the road with approx. 110 N (approx. 10 kg). In comparison, a conventional roof box pulls the vehicle slightly upwards. This results in less traction when driving on the highway and thus poses an increased risk of accidents, especially on wet roads. The result can be illustrated as follows:
Conventional roof box with large dead water area (black area)
Conventional roof boxes exhibit high turbulence intensity (turbulent = bad) in the rear area. This results in a large so-called dead water area, which occupies approx. 1/3 of the roof box length before the streamlines converge again in a laminar (laminar = good) manner. Such turbulent effects have a negative impact on the performance of the roof box and cause increased fuel/energy consumption due to the negative pressure that forms.
ASPHALTKIND roof box with significantly smaller dead water area
The aerodynamic teardrop shape of the ASPHALTKIND roof box significantly reduces flow separation at the rear, resulting in significantly lower fuel/energy consumption. The overall result is a much more homogeneous flow model with a pronounced laminar flow. Almost like a penguin.
Of course, the general rule is that only perfect aerodynamics combined with high stability through the use of carbon fiber make it possible to drive a (super) sports car on a road trip, a road trip, or even on the way to vacation without compromising on speed.