Which Indian cars are best aerodynamically

Cars: tiny things against the wind - aerodynamics of cars are becoming more important

They are fighting for every thousandth behind the decimal point: After car manufacturers have fought against the excess weight of their models in recent years, they are now working harder on the drag coefficient. Because together with the frontal area of ​​a car, it defines its air resistance. And the lower it is, the less fuel a car uses. The highlight of the matter: Optimizations in the fight against the wind can be implemented comparatively inexpensively.

"The lower the drag coefficient, the lower the CO2 emissions", says Prof. Jochen Wiedemann from the Research Institute for Automotive Engineering and Vehicle Engines in Stuttgart (FKFS). And Teddy Woll, who heads aerodynamics development at Mercedes in Stuttgart, says: "An improvement in the drag coefficient by 0.01 means one gram less CO2 per kilometer in the test cycle." For the higher consumption in everyday life, this means: The CO2 savings also increase - in this example to around two grams. And because the influence of the drag coefficient increases with speed, the savings climb to five grams less CO2 at 150 km / h, so wool.

The VW XL1, for example, shows what is possible in the fight against the airstream. With a drag coefficient of 0.189, according to the manufacturer, the one-liter car is currently the most aerodynamically efficient vehicle on the market, even though it is only produced in a small series. The Lower Saxony have chosen a flat and slim body shape that tapers towards the rear. "We have fine-tuned every detail," says Steven Volckaert from VW Development. Every joint in the body was closed and the underbody was covered. The exterior mirrors replace small video cameras. "That alone saves a tenth of a liter."

The lids on the rear wheel arches of the XL1, under which only a few centimeters of the tire protrude, are also streamlined. However, because this creates problems with the cooling of the brakes and is not particularly practical in the event of a flat tire, alternatives have become established in large-scale production.

This is how Mercedes invented the "aerodynamically optimized wheel arch". According to chief aerodynamicist Woll, it is one reason that the new CLA has a drag coefficient of 0.22 at best, making it the current record holder among mass-produced vehicles. A comparatively inconspicuous component has the greatest effect: the jagged wheel spoiler. The plastic lip mounted on the underbody in front of the wheels reduces disruptive turbulence in the wheel arches - for example, by deflecting the air flow away from the wheels.

"Air Curtain" and "Air Breather", which are finding their way into more and more BMW models, are also intended to counteract the disturbing turbulence in the wheel arch. The "Air Curtain" is a curtain of air that is created through slits in the bumper and is placed in front of the wheel. And as "Air Breather" the Bavarians refer to the sheet metal slot in the fender through which air is directed out of the wheel arch. "Starting with the 3 Series GT, we are now bringing this to many models," says Head of Design Adrian van Hooydonk.

Ford goes one step further with the Atlas pick-up study: There the rims have movable flaps that close the slots between the spokes when the brakes do not need to be cooled. That is a good approach, says Prof. Wiedemann. A quick series implementation is unlikely for reasons of cost. There are also still technical problems to be solved that arise from dirt and snow.

"But you don't even have to go that far," says the expert: Just by choosing the tire, significant improvements in the drag coefficient can be achieved. Studies by his institute had shown differences in the drag coefficient of more than 0.01 in the case of identical dimensions simply through the design of profile and flank.

According to Wiedemann, there is a simple reason why the aerodynamicists and their ideas are more heard by the car manufacturers than before: "Their approaches promise a great effect and are comparatively cheap to implement," he says with a view to alternatives such as lightweight bodies or hybrid and Electric drives.

An example: According to Wiedemann, 10 percent less vehicle weight results in 6 to 7 percent less CO2 emissions in the standard cycle. In the case of a compact car, that would be a weight loss of more than 100 kilograms, which can only be achieved with an investment of around 1000 euros per vehicle. In order to achieve the same effect with the help of aerodynamics, the drag coefficient must be reduced by 20 percent, according to Wiedemann. But that doesn't even cost half as much, because all you need is plastic cladding, spoilers and simple changes in shape. Mercedes employee Woll is even clearer: "A streamlined shape does not cost a cent more than an unfavorable one. Therefore, there is no cheaper way to save CO2." (dpa)