Semi-autonomous driver assistance tech is also optionable, with a £595 package that adds lane keeping and blind spot assists, while the £1695 Driving Assistance package adds adaptive cruise control and a pre-safe system that prepares the car for an accident if an imminent collision is detected.
Mercedes-AMG GT R smashes rear-wheel drive Nürburgring record
Sporting the styling updates unveiled on the 577bhp GT R back in June, the GT Roadster features AMG’s distinctive new 300 SL Panamericana inspired grille, which receives an altered shape and vertical chrome bars instead of the earlier blade treatment seen on the GT Coupé.
To ensure more efficient cooling of the engine and improved aerodynamic properties, the GT Roadster also adopts the active air management system that was first seen on the GT R. It uses a series of vertical louvres within the grille, which automatically open and close depending on the temperature of the engine to either enhance cooling or smooth airflow.
Further visual changes over the GT Coupé include a more defined splitter element in the lower section of the front bumper, larger air ducts and more defined sills underneath the doors.
At the rear, the two GT Roadster models differ in width due to the adoption of differing rear bumpers. The standard GT Roadster uses the same bumpers as the existing GT Coupé, while the GT C Roadster uses the 57mm wider bodywork of the GT R. This allows the latter to run larger 20in rear wheels with 305/30 profile rubber as standard in place of the 19in rims and 295/35 tyres of the former.
As with its predecessor, the SLS Roadster produced between 2011 and 2014, the GT Roadster features an automatic fabric roof. The three-layer structure, which comes in either black, red or beige, is supported by a frame made from aluminium, magnesium and steel. It opens and closes in a claimed 11sec at speeds up to 31mph, folding and stowing over the rear bulkhead behind the two-seat cabin.
Offsetting the loss of a fixed roof structure is a stiffened the aluminium body structure with thicker sill elements, an additional dashboard support and a new aluminium crossmember supporting a fixed roll over bars.
Significantly, the GT Roadster packs greater reserves than the GT Coupé to counteract the higher kerb weight brought on by its electrically powered fabric roof and the structural stiffening measures required to accommodate it.
The third model in the GT line-up shares its twin-charged 4.0-litre V8 petrol engine with AMG’s headlining coupé. But while the 90deg unit delivers 456bhp in the GT Coupé and 502bhp in the GT S Coupé, its outputs have risen a respective 13bhp and 47bhp, giving the GT Roadster 469bhp and the GT C Roadster a heady 549bhp.
Torque is also up, extending by 22lb ft in both the GT Roadster and GT C Roadster to 464lb ft and 501lb ft respectively.
In comparison, the twin-turbocharged 3.8-litre horizontally opposed six-cylinder powered Porsche 911 S Turbo Cabriolet kicks out 571bhp and 516lb ft.
Together with the increase in power and torque, the GT Roadster also receives altered gear ratios for its seven-speed Speedshift dual-clutch automatic transaxle. AMG says the new open-top features a higher first and lower seventh gears, as well as a lower final drive than the existing GT Coupé.
The rear-wheel-drive GT Roadster offers four driving modes as standard via a so-called Dynamic Select controller: Comfort, Sport, Sport Plus and Individual. The more performance focused GT C Roadster adds a fifth mode, Race.
With a power-to-weight ratio of 294bhp per tonne, the 1595kg GT Roadster is claimed to hit 62mph in 4.0sec and run to a top speed of 188mph. With 331bhp per tonne, the more powerful 1660kg GT C Roadster is claimed to outrun the GT S Coupé to the tune of 0.1sec and 3mph, with an official 0-62mph time of 3.7sec and 196mph top speed.
Corresponding fuel consumptions are put at 30.0mpg and 24.8mpg for CO2 emission ratings of 219g/km and 259g/km.
AMG explains the 65kg weight difference between the GT Roadster and GT C Roadster due to the latter receiving a higher level of standard features. Included is the rear-wheel steering system first unveiled on the GT R. It steers the rear wheels in the opposite direction to those up front at speeds up to 62mph to enhance agility and reduce the amount of steering input that is required to turn into corners. Once the speed exceeds 62mph, the rear wheels then turn in the same direction as those at the front in a move that is claimed to enhance longitudinal stability without any reduction in overall steering response.
As with the GT Coupé, the two GT Roadster models feature differing suspension set-ups. The standard GT Roadster model receives a so-called sports suspension with fixed rate damping, with the GT C Roadster boasting AMG Ride Control with adaptive damping.
Although Mercedes-AMG refuses to comment, German dealer sources confirm the altered styling, more powerful engine and altered gearbox ratios of the GT Roadster models will feature in a facelifted version of the GT Coupé.
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