The Kia Stinger is entering the final stages of its rigorous test and development regime before going on sale later this year. The test program – carried out worldwide, on-road and on-track – will ensure the car has the performance, reliability and dynamic sophistication to match its striking fastback design.
Aerodynamics: realizing the Stinger’s gran turismo design
Unveiled at the 2017 North American International Auto Show, the Stinger made a bold first impression. “The new Kia GT is a true gran turismo, a car for spirited long-distance driving,” explains Gregory Guillaume, Kia Motors Europe’s Chief Designer. “It’s not about outright power, hard-edged dynamics and brutal styling all at the expense of luxury, comfort and grace. The new GT has nothing to do with being the first to arrive at the destination – this car is all about the journey. It’s about passion.”
In realizing the Stinger’s production design – a fastback shape embodying grace, flair and dynamism – Kia’s designers were also guided by the company’s aerodynamics experts. In general, fastback bodies can pose more challenges during aerodynamic optimization compared to conventional designs. Therefore, close and intense collaboration is required between designers and aerodynamicists to realize the desired shape. Kia’s Frankfurt R&D centre used computational fluid dynamics (CFD) software to quickly test and validate different ideas to enhance the car’s aerodynamic profile, while retaining the fastback silhouette.
After four weeks of collaboration between designers and engineers, subtle design changes were introduced to improve air flow over the car. The bodywork was tapered slightly towards the rear of the car and new ‘gills’ were introduced behind the front wheel arches, each serving to reduce wake turbulence as air passed over the car’s flanks. A partially-flat underfloor cover, flowing into the rear diffuser, was deployed to reduce drag under the car, while the rear spoiler was remodeled with a slight ‘ducktail’ shape, reducing lift and increasing high-speed stability. At the front, larger horizontal cooling ducts were introduced to optimize brake cooling, and air inlets were shaped to reduce front-end lift. Finally, Kia’s aerodynamicists found that, by reducing the height of the rear of the roof, they could enhance the fastback’s ‘aerofoil’ shape and improve the Stinger’s aerodynamic efficiency at the same time.
Design finalized, the Stinger was ready for its first on-road tests.
Ride and handling: a gran turismo for all conditions
The Stinger’s dynamics presented Kia engineers with a new challenge. As a car without a predecessor, Kia’s chassis engineers were given a blank canvas for the car’s suspension and steering characteristics. Their brief: to create a true gran turismo, with driving dynamics to match the car’s fastback design. The shape of the car has inspired efforts to imbue the Stinger with agile handling and high levels of body control, delivered to provide rewards for the more enthusiastic driver. Meanwhile, the ride needed to deliver a balance of everyday compliance and high-speed cruising comfort.
To meet this brief, Kia’s engineers developed two different types of suspension. Every Stinger is suspended by MacPherson struts at the front, and fully-independent multi-link suspension at the rear. However, the ‘clean sheet’ approach to the car’s development has allowed 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 shock absorbers on the move, and is controlled by acceleration, braking and steering sensors.
Drivers can change the characteristics of the Stinger’s shock absorbers. Using the Stinger’s Drive Mode Selector system, drivers have a choice of two damping force levels: ‘Normal’ and ‘Sport’. In ‘Normal’ mode, low levels of damping force enable maximum cruising comfort. While the suspension continues to firm up slightly under heavy cornering in ‘Normal’, the effect is less pronounced than in ‘Sport’ mode. The driver’s choice, ‘Sport’ provides more powerful damping force under all conditions, shortening the stroke of the shock absorbers to provide greater body control and handling agility during more spirited driving. DSDC will be fitted as standard to 3.3-litre V6 Stinger models.
The passive suspension – fitted as standard to 2.0-litre turbo gasoline and all 2.2-litre diesel models – was designed to the same brief as the DSDC system. A single-mode passive setup, the standard suspension has been verified alongside DSDC at the Nürburgring Nordschleife and on the road, offering confidence at a cruise and on winding roads. Based on Kia’s most refined multi-link suspension concept, the Stinger’s suspension has been redesigned with stiffer springs and stabiliser bars for more immediate handling responses.
Much of the suspension tuning has focused on creating a uniform character across the Stinger range – regardless of engine weight and the car’s rear- or all-wheel drive drivetrain configuration. While this means that all-wheel drive models offer a similar dynamic character to rear-wheel drive models, the all-wheel drive cars offer increased damping force and revised shock absorber settings for the rear axle, better planting the rear wheels to the road and enabling the car’s rear-drive character to shine through.
The Stinger’s rack-mounted motor-driven power steering system (R-MDPS) provided chassis engineers with greater flexibility for tuning. Fitted as standard to every Stinger, R-MDPS lets drivers choose between two steering modes with the Drive Mode Selector – ‘Normal’ and ‘Sport’. These modes change the level of steering effort required, as well as the system’s variable steering ratios.
In ‘Sport’ mode, the Stinger requires increased on-centre steering effort, with shorter gearing providing more immediate response by reducing the need for larger steering inputs. ‘Normal’ mode reduces steering effort from on-centre, 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 giving driver’s greater confidence at the wheel. The result is a steering system that enables 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 have also undergone a further level of dynamic testing in the UK, to optimize steering and suspension components for certain markets – such as the UK and Australia – before the car’s release.
Brakes: stopping Kia’s highest-performing car yet
Producing 370 ps, the Kia Stinger’s 3.3-litre twin-turbo V6 enables the car to accelerate from 0-to-100 kph in just 4.9 seconds, making it the fastest-accelerating production Kia ever. Its high-performance brakes needed to be equal to the task.
Targeting the highest braking performance of any Kia to date, engineers subjected the Stinger to a variety of high-speed braking tests. A rigorous range of braking challenges was devised, taking brake testers to 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.
Not only did the Stinger’s brakes have to offer objectively strong and consistent braking power, Kia’s R&D teams wanted to maintain a reassuring, responsive feel to the pedal, even after repeated heavy braking, for maximum driver confidence. More development work has been carried out on the Stinger’s brakes than any previous Kia car.
High-powered 3.3-litre Stinger models feature a new braking system developed in collaboration with Brembo. The 18-inch Brembo disc brakes are designed specifically to meet the demands of the engine’s higher power output. Holed and grooved, the brakes offer high heat capacity and reduced fade levels under heavy use. They’re paired with the most powerful calipers ever found on a Kia.
Very early in the Stinger’s development, engineers had considered carbon ceramic brakes to maximize the grand tourer’s braking power. However, as a Kia, the Stinger needed to remain affordable, both to buy and maintain, for customers around the world. Brembo’s high-carbon 18-inch steel brakes proved more than up to the job of bringing the Stinger to a halt, however. 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 Stinger’s Brembo brake system, with temperatures rising above 800°C (over 1,472°F). Even at these temperatures, the Stinger’s brakes continue to offer consistent braking power and pedal feel.
Quality and reliability: taking on the ‘Green Hell’
Like every Kia, the Stinger is undergoing a full, rigorous testing regime to ensure it is as reliable for owners as it is entertaining for drivers. While the Nürburgring Nordschleife has played a key role in establishing the Stinger’s dynamic character, Kia’s testing facility at the ‘Green Hell’ also sees every car tested for quality and reliability.
Each development car is being put through a minimum of 10,000 km – 480 laps – of high-stress driving around the Nordschleife. Widely regarded as the ultimate proving ground, the circuit has 73 corners, a 300-metre difference in height between the highest and lowest points of the circuit, and gradients of up to 17%. The constant combination of hard acceleration, rapid deceleration, heavy cornering, and changing surfaces and camber offers an unrivalled test of dynamic prowess. This distance covered during the Stinger’s development is equivalent to over 160,000 km of on-road testing.
Every Stinger prototype tested at the Nürburgring Nordschleife is treated to the same punishing regime, testing the suspension, body and powertrain to the full. Kia’s testing procedures are designed to identify powertrain wear and fluid leaks in particular, as well as gearbox heat management characteristics. Temperatures of the car’s brakes, exhaust and gearbox are constantly monitored, to make sure they consistently offer optimal performance. The brakes, for instance, have to be changed halfway through a typical daily session, such is the harsh nature of the tests to which development prototypes are subjected.
The 3.3-litre Stinger is currently in its final testing phase at the Nürburgring Nordschleife, but much of the development work for the 2.0- and 2.2-litre powertrains – rear- and all-wheel drive – has been completed. One diesel prototype completed 20,000 km of testing around the Nordschleife. The engine had already completed the full 10,000 km testing distance, but further development work to the chassis meant engineers needed to test a series of new components. New parts fitted, the same powertrain – gearbox and engine – remained, going on to complete a second 10,000 km testing run. Fully run-in, the engine worked as well at it had at the start of the test.
The Stinger’s eight-speed automatic transmission, available with each of the three engines, was a key focus for powertrain testing. Nordschleife testing identified a need to more efficiently manage heat in the transmission – early tests revealed the oil temperature was rising higher than preferred by the engineers. To counteract this, Kia engineers fitted the transmission with an oil cooler with a larger surface area to enable more efficient cooling.
Beyond the Nürburgring, testing for the Stinger was carried out globally, with over 1.1 million km of durability testing carried out around the world – equivalent to approximately 27 circulations of the Earth around the Equator.
The car’s development took place across Europe, the Middle East, Asia and North and South America, for extreme climate testing and quality verification for all components used in the Stinger. Tested for a global audience, the Stinger was subjected to extreme cold and heat and high altitude, and faced up to the unique demands of the desert, congested city centers, mountain passes and permafrost regions.
Refinement: creating the consummate grand tourer
The consummate gran turismo, the Kia Stinger‘s on-road refinement is particularly important. Equally important, however, is the desire of customers to enjoy the sound of the engine at work. The Stinger is the first Kia to be fitted with a new active sound system, enhancing the engine note of the car via the car’s sound system rather than via an actuator which ‘channels’ noise into the cabin.
Engineered in Europe, the sound is designed to be consistent with the layout of the engine, providing drivers with additional aural inputs from the powertrain to enhance the driving experience. The 3.3-litre engine authentically enhances the distinctive V6 engine note in the cabin, while the 2.0-litre gasoline lets drivers enjoy the sportier character of the four-cylinder engine under acceleration. The active sound system also refines the sound of the 2.2-litre diesel engine, masking certain elements of the engine’s sound and enhancing others for a more refined engine note.
Sound engineers have paired the system with the 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 from the system’s ‘Eco’ mode, through ‘Normal’, ‘Sport’ and ‘Sport+’ in Europe, and ‘Custom’ in US and other countries.