Vauxhall’s mid-size coupe challenger caused a stir when it became available to order in June. With a starting price of just £18,495 and dramatic styling from a design team led by Brit, Mark Adams, the GTC is set to wow UK customers and rock the established front runners in its class – the Volkswagen Scirocco and the Renault Megane Coupe. But the GTC’s appeal runs far deeper than its rakish lines. Unlike many three-door versions of existing compact hatches, the GTC – like the Astra Sports Hatch before it – will be a standalone model in Vauxhall’s range, conceived to resonate with a more driver- oriented customer base who value the way a car handles and performs as much as the way it looks.
To do this, engineers from both Vauxhall Engineering Centre at Millbrook and Opel in R*sselsheim have developed a bespoke platform for the GTC. Key components – such as the HiPerStruts used on the front axle – have been derived from the 325PS Insignia VXR, while significant upgrades have been made to the GTC’s unique Watt’s link/compound crank rear end. So while the GTC line-up currently includes a broad range of engines producing from 120 to 180PS, drivers can always be assured of class-leading levels of dynamic control.
But the best chassis can only be honed through intense testing on the most demanding surfaces. Britain will be by far the biggest market for the GTC, which is why Vauxhall and Opel engineers have conducted much of their evaluation on UK roads, with their unique (and some may say diabolical) blend of undulations, cambers, rough surfaces, blind apexes and crests. The theory is this: if the GTC can work well in the UK, it will work much more effectively on other markets’ roads, too.
High tech front suspension boosts GTC’s appeal
From the start of the GTC’s development programme the target was to deliver a driver-oriented feel to the car, and one that worked well on UK roads. “Our aim was to exceed the best in class with the GTC’s dynamics,” said Gerry Baker, Vauxhall Engineering Centre’s chief dynamicist. “We also wanted to change the emphasis in steering and damper feel from the regular Astra Hatch to a set-up that was more focused, yet still comfortable enough for British roads and drivers.”
Much of the development centred around the introduction of Vauxhall’s HiPerStrut to the GTC, a first for an Astra model. Based on the system currently seen on the 325PS Insignia VXR, the HiPerStrut uses the Astra’s existing pick-up points, but reduces the kingpin inclination angle by 44 per cent and shortens the spindle length (kingpin offset) by 46 per cent versus the MacPherson strut-equipped models. This helps prevent torquesteer – a trait of many powerful front-wheel-drive cars – allowing drivers to make more use of the GTC’s performance without the steering being corrupted.
Adding the HiPerStrut has also reduced the amount of camber change on the GTC’s front wheels during cornering, improving grip. Steering feel is enhanced, too, helped by a reduction the steering system’s friction levels. The geometry changes brought by the HiPerStruts also mean that the GTC can be fitted with wheels of up to 20-inches in diameter.
“The current Astra Hatch has always handled exceptionally well,” said Michael Harder, Vehicle Dynamics Supervisor at Opel. “But with the GTC, we’ve raised the bar still further. Drivers will instantly appreciate the extra level of involvement – and grip – allowing them to exploit the potential of the basic Astra platform still further.”
Rear suspension revisions complement GTC’s ride-height & track changes
Compared with the Astra Hatch, the GTC’s ride height has been lowered by 15mm, while the wheelbase has grown by 10mm, from 2685mm to 2695mm. Both tracks are wider, too, at 1584mm (+40mm) front and 1585mm (+30mm) rear.
The Astra’s GTC compound crank/Watt’s link rear suspension system has also been revised, with bespoke roll-stiffness and roll-centre height settings for this application. The system has many advantages over a modern multi-link design, including improved packaging, greater wheel camber stiffness and reduced suspension friction. The Watt’s link also ensures that lateral stability is maintained at all times.
The Watt’s link is carried on a small cross-member attached to the underside of the car, just behind the rear wheel centre line. It comprises a short, pivoting centre link with a ball joint at each end, to which the lateral links from the wheels are bolted.
In a straight line, the set up ensures excellent stability, but during cornering it minimises lateral deflection in the same way a modern multi-link system would do. Vauxhall’s engineers estimate that the linkage absorbs around 80 per cent of all lateral loadings on the rear suspension. In addition, the Watt’s link allows for softer bushings, which no longer have to compensate for toe changes at the rear of the car, and thus provide greater compliance and ride comfort from the rear axle.
Unique steering programme for UK drivers
Precision, Feedback & Confidence. These were the three target elements for the GTC’s UK-specific steering programme. The challenge was to maintain the system’s ease of use at lower speeds, but dial in a greater degree of involvement and slightly more effort at higher speeds.
The Astra GTC uses a rack and pinion steering system with speed sensitive assistance. But in order to provide drivers with more steering feedback, the system’s electric motor is mounted directly on the steering rack, as opposed to the base of the steering column.
The key benefits of using an electric power steering (EPS) are well known. At low speeds, the level of power assistance is increased to minimise steering effort. At higher speeds, assistance is automatically reduced to ensure a high degree of steering feel for the driver. The second important benefit is that, because it does not require an energy consuming hydraulic pump and responds directly to the amount of power needed at any speed, fuel consumption is also reduced.
FlexRide enhances GTC’s driver appeal still further
FlexRide, Vauxhall’s adaptive damping system, will be available as an option across the GTC range, complementing the significant revisions to the new model’s chassis. FlexRide automatically adapts to prevailing road surfaces and driving styles, providing drivers with fully optimised handling, even in the event of an emergency situation.
At the heart of FlexRide is the Driving Mode Control (DMC) which oversees and executes the system’s settings, allowing the car to react to sudden changes in driving style or emergency situations. For example, if the driver needs to avoid an obstacle while in ‘Tour’ mode – the softest of the three settings – chassis sensors convey this to the DMC and the dampers are adjusted in a split second.
Standard mode (the default setting) reacts in the same way as Tour, but when drivers select Sport they not only get stiffer dampers, but more steering effort, sharper throttle response and an instrument panel that’s back-lit in red, rather than white. Each of these settings can be dialled in or out of Sport mode via the GTC’s configurator.
British roads: the ultimate challenge for dynamicists!
Vauxhall and Opel engineers are making increasing use of British roads as a key part of their overall chassis development programmes. In the last three years, the Insignia, Astra, Astra Sports Tourer, Meriva, and now the Astra GTC, have all benefited from the UK’s unique mix of road surfaces.
So what makes our roads so bad, but so good for chassis engineers?
“Our road system is like no other in Europe,” said Gerry Baker. “We obviously test cars in many different countries, but the UK’s severely undulating and heavily cambered roads often reveal handling traits that would otherwise be hidden on smoother surfaced and more predictable continental roads.
“It’s not just the surfaces, either. Corners with changing radii are commonplace in the UK, as are blind apexes and crests, which mean that extra demands are put upon our cars and drivers. A good example is a driver who has to make a mid-corner adjustment on an unfamiliar road where the bend tightens unexpectedly and he throttles-off or brakes suddenly. The car needs to work with him, and respond intuitively to steering inputs, but it still needs to be rewarding to drive under normal conditions.”
Recognising that British drivers don’t always have access to winding, smooth-surfaced roads, the GTC has also been tuned to deal with the worst rutted and broken surfaces, even when equipped with its optional 19- and 20-inch wheels (18-inch wheels are standard).