The Nürburgring Nordschleife (North Loop) became known as 'The Green Hell' for very good reasons. It runs for more than 13 miles through the Eifel mountains in Germany, and contains 73 corners, a 300-metre difference in height between its highest and lowest points, and has gradients of up to 17 per cent.
Driving round it demands constant hard acceleration and braking and heavy cornering. There are changing surfaces and cambers offering an unrivalled test of a car's dynamic prowess. As a test facility it is merciless, which is why Kia has established a base there. Every new model – including Stinger – is tested there to hone its suspension, steering and brakes. The testing regime was so punishing that brake pads had to be changed half way through each day.
During the development of Stinger, prototypes were put through at least 10,000 km, or 480 laps, of high-stress driving around the Nordschleife – not to set a lap time which would be irrelevant to customers, but to ensure the finished product would be a genuine gran turismo. One diesel prototype completed 20,000 km around the Nordschleife. The engine had already covered the full 10,000-kilometre testing distance, but further work to the chassis meant engineers needed to test a series of new components. With new parts fitted, the same powertrain completed a second 10,000-kilometre run.
The automatic transmission was a key focus for powertrain testing. Nordschleife testing identified a need to manage heat in the transmission more efficiently: initially, the temperature of the gearbox oil was rising higher than what was deemed acceptable by the engineers. To counteract this, an oil cooler with a larger surface area was adopted.
Stinger’s dynamics presented the engineers with a new challenge. Because this was going to be a totally new kind of car for Kia, the chassis engineers were given a blank canvas for the suspension and steering characteristics. Their brief was to create a true gran turismo which would drive the way it looks. The shape of the car inspired efforts to imbue Stinger with agile handling and high levels of body control for enthusiastic driver, but with a compliant ride that would ensure high-speed cruising comfort over long distances.
Two different types of suspension resulted. Every Stinger has MacPherson struts at the front and fully-independent multi-link suspension at the rear. However, the ‘clean sheet’ approach allowed the engineers to create both a traditional passive setup and a new adaptive system – Dynamic Stability Damping Control (DSDC). DSDC adapts the stroke length of the dampers on the move, and is controlled by acceleration, braking and steering sensors.
Drivers can change the characteristics of the shock absorbers via the Drive Mode Selector, which offers five modes - Eco, Normal, Sport, Sport + and Smart settings. In Normal mode, low levels of damping force ensure maximum cruising comfort. The suspension continues to firm up slightly under heavy cornering, but the effect is less pronounced than in Sport mode. DSDC is fitted as standard to the 3.3-litre V6 Stinger.
The passive suspension was designed to the same brief as the DSDC system. It was verified alongside DSDC at the Nürburgring Nordschleife and on the road. It is based on Kia’s most refined multi-link suspension, but has been redesigned with stiffer springs and stabiliser bars for more immediate handling responses.
Stinger’s rack-mounted motor-driven power steering system (R-MDPS) provided the chassis engineers with greater flexibility for tuning. Fitted to theStinger GT S, R-MDPS lets drivers choose between two steering modes via the Drive Mode Selector: Normal and Sport. These modes change the level of steering effort required, and also the variable steering ratio.
In Sport mode, Stinger requires increased on-centre steering effort, and has shorter gearing, reducing the need for larger steering inputs. Normal mode reduces the steering effort from the on-centre position for more measured steering responses at a cruise. Normal mode also requires more effort as the steering wheel turns, with a linear build-up of resistance to give drivers greater confidence. The result is a steering system providing the same duality as the suspension – one that’s as relaxing and confidence-inspiring to use in a straight line as it is immediate and engaging on more enjoyable roads.
Right-hand-drive versions of the Stinger were put through a further level of dynamic testing in the UK to hone the steering and suspension for the country's uniquely challenging roads.
The 365bhp 3.3-litre twin-turbo V6 in the Stinger ’GT S’ enables the car to accelerate from 0 to 60mph in just 4.7 seconds, making it the fastest-accelerating production Kia ever. Its high-performance brakes therefore needed to be equal to the task.
To ensure this would be the case, a rigorous range of braking challenges was devised, taking in the famous Grossglockner High Alpine Road in the Austrian Alps for constant downhill brake testing. Private test facilities in Northern Germany and Eastern Spain, as well as the Nürburgring, were also used.
Stinger’s brakes not only had to offer strong and consistent braking power. A reassuring and responsive feel to the pedal was also demanded by the engineers, even after repeated heavy braking, for maximum driver confidence. More development work has been carried out on the Stinger’s brakes than on any previous Kia.
The ’GT S’ features a new braking system developed with Brembo. The 350mm front and 340mm Brembo discs are holed and grooved, providing high heat capacity and reduced fade levels under repeated heavy use. They are paired with the most powerful calipers ever found on a Kia.
Early in Stinger’s development, engineers considered carbon ceramic brakes to maximise the braking power. However, as a Kia, Stinger needed to remain affordable to buy and maintain. Brembo’s brakes proved more than up to what was required of them.
Kia’s internal tests are designed to validate brakes at temperatures of up to 700°C (1,292°F). Engineers went even further for the Brembo brake system, with temperatures rising to more than 800°C (1,472°F). Even at these temperatures, Stinger’s brakes continue to offer consistent braking power and pedal feel.
Kia did not confine Stinger testing to the Nürburgring. Prototypes have been driven for more than 1.1 million kilometres – the equivalent of 27 times around the Equator – to test Stinger'sdurability. Extreme climate testing took place across Europe, the Middle East, Asia and North and South America. Stinger was subjected to extreme cold and heat and high altitude, and faced the unique demands of the desert, permafrost regions, congested city centres and mountain passes.
Stinger was plunged into Arctic winters to ensure predictable, stable, gran turismo handling in all conditions with the engaging, fun-to-drive character of a rear-wheel drive car. From the development facility in Arjeplog in Swedish Lapland, Kia honed Stinger in a range of low-grip environments, including a skid-pan, handling circuit and slalom test on the surface of the frozen Uddjaure lake. Kia’s winter test regime saw the car being driven in temperatures as low as -35°C (-31°F).
Stinger‘s on-road refinement was equally important, but customers also want to enjoy the sound of the engine at work. Stinger is the first Kia with an Active Sound system to enhance the engine note via the car’s audio rather than through an actuator which channels noise into the cabin.
The Active Sound system was engineered in Europe and is consistent with the type of engine. The 3.3-litre engine authentically enhances the distinctive V6 engine note, while the 2.0-litre T-GDi lets drivers enjoy the sportier character of the four-cylinder unit under acceleration. The system also refines the sound of the 2.2-litre diesel engine, masking certain elements and enhancing others for a more refined note.
Sound engineers have paired the system with Stinger’s Drive Mode Selector, enabling drivers to change the level of engine noise in the cabin. The sound becomes slightly louder and more aggressive in tone as drivers switch modes.
Albert Biermann, Kia’s Head of Vehicle Test and High Performance Development, says: “Testing the car in extreme conditions allowed us to focus on its stability and predictability in every configuration and in all driving conditions. Crucially, these tests allowed us to engineer a car which retains the driving appeal that buyers look for in a gran turismo. We want enthusiastic drivers to be able to enjoy the thrill of driving their Stinger in all conditions without compromising on safety.”