"Good vibrations" with Opel

"Good vibrations" make the difference High-tech shock absorbers in DTM touring cars offer virtually infinite set-up options Heavy bumps at the Norisring or a completely flat track at the EuroSpeedway Lausitz -- the suspension springs and, first...

"Good vibrations" make the difference
High-tech shock absorbers in DTM touring cars offer virtually infinite set-up options

Heavy bumps at the Norisring or a completely flat track at the EuroSpeedway Lausitz -- the suspension springs and, first and foremost, the shock absorbers play a crucial role in ensuring that the 460-hp touring cars never lose optimal touch with the ground. "A spring is still a spring, but shock absorbers, which are now adjustable in virtually every respect, have seen incredibly fast technological advancement," says Opel works driver Joachim Winkelhock, emphasising the importance of the dampers.

"Good vibrations," in a manner of speaking, are crucial. "Shock absorbers convert the vibrational energy generated by the suspension springs as they cushion the vehicle body against the road into thermal energy," explains Marco Gehlen, engineer and damper specialist with Opel Team Phoenix.

Perception can be deceiving

Working on springs and shock absorber settings, the Opel drivers in conjunction with their vehicle engineers fine-tune the specific set-up to be used for the respective race track. Of course, this includes other set-up parameters like toe, camber, castor angle, anti-roll bars, aerofoils, etc. "Fine-tuning the shocks is performed by such minute "notches" that the results can only be verified through data analysis, and rarely by the driver's perception," says 'Jockel' Winkelhock (Opel Team Phoenix). "A smooth set-up can be deceiving," adds Timo Scheider (Opel Team Phoenix). "You'll be enjoying a comfortable ride but the disadvantages will show in your lap times."

In-depth rig tests

As a general rule, the efficacy of the shock absorbers is investigated during in-depth rig testing prior to any DTM race. This includes the development of different parameters, depending on the characteristics of the circuit as well as the individual needs of the drivers.

Racing shocks can be adjusted externally, enabling their performance and efficacy to be modified even on short notice. Generally speaking, shock absorbers have a bi-directional effect, i.e. the bump and rebound stages. For both directions of travel there are two speed ranges: bump low speed and bump high speed, rebound low speed and rebound high speed. The force is generated at the moving main piston and, additionally, at the compression stage valve. "Damper parameters are extremely complex. Any type of progression can be adjusted. The initial and follow-on travel of the wheel suspension can even be adapted to the special characteristics of corners," says Timo Scheider.

Fine-tuning during practice sessions

Whether the vehicle will have a softer or stiffer set-up primarily depends on the race track. "The Lausitz-Ring, for example, is very flat and has no high kerbs. That's why the shock absorbers in particular can be set for higher stiffness because, on the EuroSpeedway, they don't have to respond to sudden bumps," says Alain Menu (Opel Euroteam), who is ranking sixth in the DTM standings prior to the sixth DTM race this coming weekend. The hairpin bend at the Lausitz-Ring, which leads back to the start and finish line via the banked corner, will be a crucial point for the vehicle set-up. "The question is how far you can take stiffness with your set-up and at what point you will lose too much time in the hairpin, because a softer set-up would actually improve traction."

Compromise between aerodynamic and mechanical grip

The shock absorbers are adapted to the respective suspension spring. The optimal selection of the spring rate -- in racing, spring rates of up to 200 newtons per millimetre (N/mm) are being used, whilst production vehicles have spring rates between 20 and 60 N/mm - requires a compromise between aerodynamic and mechanical grip. "Aerodynamics require stiff springs in order to keep the ride height as constant as possible to achieve steady downforce," says Dr Ulrich Pfisterer, DTM project manager with Opel Performance Center (OPC).

Mechanical grip is increased by a soft set-up, enabling the wheel to optimally follow any bumps on the ground. Production vehicles have no downforce in this sense of the word. Instead, ride comfort, which is decisively influenced by the shock absorber configuration as well, is of critical importance.

Shock absorbers as a high-tech component

Racing shocks are high-tech components manufactured in extremely small volumes. In addition to performance and adjustment options, light-weight design and optimised friction resulting from the use of special seals are important considerations. It thus comes as no surprise that the price of a shock absorber designed for racing is about 50 times higher than that of a high-volume production shock used in road cars. DTM regulations, by the way, prescribe so-called coil overs with the spring concentrically located around the damper. For that reason, the damper has been designed to enable the spring to be quickly exchanged during tests and practice sessions.

"Finding the right compromise and optimal vehicle balance is a difficult task," says Manuel Reuter (Opel Team Phoenix). "After all, springs and dampers are only two of numerous parameters involved in the vehicle set-up." A simple "click" on a small adjustment knob -- and the damper changes its efficacy. "As a driver I don't concern myself with the complexity of the shocks, but only with the results of their work," says Manuel Reuter, who had the right "click" when driving his Opel Astra V8 Coupé to pole position at the DTM race in Donington.


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About this article
Series DTM
Drivers Joachim Winkelhock , Manuel Reuter , Timo Scheider , Alain Menu