Ideal test conditions since 1967: The steep-bank curve
- May 9, 1967: Expanded proving grounds on the premises of the DaimlerChrysler plant in Untertürkheim presented to the press
- Steep-bank curve permitting high-speed and endurance tests
- Over 15 kilometers with the most diverse surfaces
The driver of the black camouflaged sedan once again puts his foot down. He accelerates the car to 150 km/h and turns into the bend. The latter “grabs” the car and turns it along its longitudinal axis into a breathtakingly inclined position. It’s as if the horizon were suddenly folded away. The body is pressed into the seat, and you no longer have complete control of your facial features. The whole racket is over after just a few seconds – the steep-bank curve turns the car back into a horizontal position upon releasing it onto the long straight. Sighs of relief all round.
The tough testing of new vehicles forms part of the preparations for large-scale production. At DaimlerChrysler, such tests are carried out all over the world. In scorching heat and extreme cold and under all conceivable environmental conditions, tomorrow’s passenger cars and commercial vehicles have to prove their mettle in everyday operation. However, tests on public roads are not always expedient, especially in the case of early prototypes. This is why there has been a dedicated test track on the premises of the Untertürkheim plant since 1956, and this test track was expanded by the addition of a spectacular construction in 1967. Since then, a steep-bank curve has also been permitting high-speed and endurance tests. The new test track was presented to the press on May 9, 1967.
The steep-bank curve with a transverse inclination of maximally 90 degrees was the solution to the space problems of the old test track in Untertürkheim. The proving grounds inaugurated in 1956 included a wide range of test facilities but was too small for high-speed and endurance testing. To be able to add these disciplines, the steep-bank curve was built, and the length of the oval was increased to 3,018 meters at the same time; the existing small lap with a length of 2,000 meters was retained. On the steep-bank curve, a maximum speed of 200 km/h is theoretically possible, but no test driver would be able to endure the centrifugal forces acting on him or her at this speed in the long run. So the speed limit in normal testing is 150 km/h – a speed at which the driver’s weight rises by a factor of as high as 3.1. At the same time as the steep-bank curve, a bridge with uphill and downhill ramps was built especially for commercial vehicles, with inclines ranging from five to 70 percent.
Added to this are washboard, torture, potholed and distortion tracks of the worst conceivable nature. One of these is a notorious torture track which is a true-to-the-original reproduction of an authentic, particularly poor stretch of road in the Lüneburg Heath in the north of Germany. Each surface is precisely documented, and when part of it is damaged under the enormous stresses of trial driving, a road builder is commissioned to restore it in accordance with the relevant specifications. Equally available are fording basins and salt baths for corrosion tests.
A skid pad with a diameter of 100 meters and seven different road surfaces is used for lateral-dynamics and powertrain tests. The outer lane of the skid pad is a steep-bank curve inclined at 20 degrees and therefore permits relatively high speeds. Equipped with all these facilities, the test track represented a big step ahead in 1967 because at last, the engineers were able to carry out test series and measurements under identical conditions, and also to take a test vehicle to breakage point without any serious risks being involved for human beings.
Another new facility added in 1967 was the crosswind machine with 16 powerful blowers for simulating and precisely measuring a vehicle’s deviation from its course under the impact of crosswind. And last but not least, novel exhaust-gas test rigs were built in response to the first emission laws which came into force in California in the 1960s. Compliance with these laws was a condition for export to the USA.
The test track proved itself in this configuration. There have been no major modifications since 1967 – an exception being a stretch of road with tramway rails, a common feature in Germany in the 1960s. This stretch of road was eventually converted into a smooth section of road with a whisper-asphalt surface for noise measurements.
The complete network of test sections on the 8.4-hectare site in Untertürkheim is 15,460 meters long and studded with radar measuring points and electronic measuring equipment. It includes sections for braking and accelerating tests on different surfaces, some of which can be flooded to reduce the friction between tire and road. The torture tracks strain passenger cars and commercial vehicles enormously – but only in this way can weaknesses be identified and eliminated prior to the start of large-scale production. The driver of the black sedan knows this, too. With great diligence, he drives lap after lap and through the steep-bank curve time and again. For him, the spectacular run is a routine job.