The Drag Reduction System (DRS) – that’s how it works
The Drag Reduction System was introduced in DTM to make for more overtaking manoeuvres. While both racing drivers and engineers love the impact of the DTM cars’ huge rear wing in the corners, they hate in on the straights. There, the carbon-fibre part is just standing in the headwind and due to its air resistance, accelerating a car to its top speed is made more difficult. The steeper the angle a DTM rear wing is adjusted in, the faster a car’s cornering speed. But at the straight, the steep-angle wing virtually outbrakes the car. And that’s exactly the point where the RDS comes into play.
The RDS allows for making optimum use of the air drag at the rear wink to produce maximum downforce to then reduce the downforce on the straights by flapping the wing down, thus making for less drag and – consequently – a higher top speed. A simple example demonstrates this effect: If you are sitting in a driving car and hold your hand out of the window to then turn it you immediately will feel the power of the head wind. And if you consider that the DTM wing is far bigger than your hand, imaging the impact the rear wing make on the car is easy.
The RDS is activated for just one purpose: the higher top speed is supposed to make overtaking easier. A useful step. After all, the DTM grid comprises 24 cars that are able to race at the virtually same pace and are driven by 24 top drivers. The logical consequence: everybody brakes at the latest possible point in time and consequently, outbraking one another is virtually impossible. Furthermore, the slipstream of today’s state-of-the-art silhouettes is far lower than the one of the cars of the 1990s. And the layout of today’s racetracks also makes overtaking more difficult. Due to safety stipulations and local building regulations, long straights are an exception and so, the DTM racers usually achieve speeds of 200kph or more only on the final third of a straight. While the impact of the slip stream only can be felt beyond 120kph. But to let you car be sucked to the vehicle in front of you to afterwards try to pass it you have to follow it at high speed for quite a while. But the majority of the straights of the modern circuits are just too short for doing so. Would the Hockenheimring, for instance, still feature its two long straights across the woods, the DTM cars still could fascinate the crowds with thrilling slipstream battles – without needing the DRS.
So, you could say that the DRS is supposed to compensate for the fact that the drivers have to – more often than not – do without the opportunity to make use of the slipstream. But it goes without saying that using the DRS wouldn’t be an advantage if anybody could use it simultaneously. Therefore, DTM’s sporting regulations define exactly, which drivers may use the DRS where and when – and how often the may push the DRS button.
During the two practice sessions, the DRS use still is unlimited. With one exception: to prevent a driver from inadvertently forgetting readjusting his flat wing before entering the next turn where he definitely would lose it, without the level of downforce he is accustomed to, three sensors monitor what’s going on in the cockpit. They make sure that the wing automatically returns to its steep-angle position. This happens in the case of high brake pressure (more than 15 bar) or when the driver lifts the throttle pedal. Furthermore, if a so-called centrifugal-force sensor detects a defined level of lateral forces. In all the three cases, the DRS is ordered to let the wing return to its steeper standard position. This adjustment change is executed by dint of compressed air that makes the wing move via a cylinder placed on a gearbox and a system of levers built into the wing pillars. For the case of a failure in the compressed-air system, the DRS adjustment mechanics have been designed in a way that the wing automatically returns to its standard position.
During the qualifying session, using the DRS is prohibited. And to make sure that everybody really abides by this regulation, the DRS mechanics have to be blocked by a big spacer ring, in the qualifying session.
For the two races of a DTM race meeting, the use of the DRS is clearly and explicitly defined. The use of the DRS generally isn’t allowed before the race leader starts into his fourth race lap. From that point in time, all those drivers whose gap to the driver ahead of them adds up to less than a second, when crossing the line, may use the DRS. The race control sends a signal to the respective cars via radio. On the following lap, a driver may activate the DRS three times and it’s up to him to decide where he does so. But there also are exceptions in the races: during a safety-car period or when yellow flags are shown, using the DRS is forbidden. This also applies to a situation when the race control allowed the use of wets.
In the sporting regulations, the description of the permitted use of the DRS ranges over two pages and in addition, there is half a page in the technical regulations. Consequently, it’s easy to understand that the drivers need the support of their engineers, during the races, to make sure that they don’t make any mistakes.