Review: Mercedes R171 SLK 55 AMG (2005-11)

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• Powerful 5.5-litre M113 V8 engine
• Supportive front seats
• High standard of interior fit and finish
• Powerful brakes

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• Suspension lacks low-speed compliance
• Nose-heavy and dynamics fall short of Porsche 987 Boxster

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Review: Mercedes R171.I SLK 55 AMG (2005-08)

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Overview

Released in Australia in March 2005, the Mercedes-Benz R171 SLK 55 AMG was a two-seat convertible with a retractable hardtop roof. Manufactured in Bremen, Germany, the rear-wheel drive R171 SLK 55 AMG was powered by a 5.5-litre V8 petrol engine that was mated to a seven-speed automatic transmission.

M113.989 V8 engine

The M113.989 V8 petrol engine had an alloy cylinder block with 97.0 mm bores and a 92.0 mm stroke for a capacity of 5439 cc, cast-in Silitec (Al-Si alloy) cylinder liners, fracture-split forged steel connecting rods, iron-coated aluminium pistons, an alloy cylinder head, a single overhead camshaft (SOHC) per cylinder bank driven by a double-roller chain, three valves per cylinder (two intake, one exhaust) actuated by roller rockers, a compression ratio of 11.0:1, two spark plugs per cylinder and a magnesium dual-length intake manifold.

The SLK 55 AMG could accelerate from rest to 100 km/h in 4.9 seconds and to 200 km/h in 17.5 seconds; its top speed was electronically-limited to 250 km/h.

AMG Speedshift 7G-Tronic transmission

For the seven-speed ‘AMG Speedshift 7G-Tronic’ automatic transmission, the gear ratios were 4.38 (1st), 2.86 (2nd), 1.92 (3rd), 1.37 (4th), 1.00 (5th), 0.82 (6th) and 0.73 (7th), while the final drive ratio was 3.06. Compared to Mercedes-Benz’s standard 7G-Tronic, the AMG Speedshift transmission:

• Provided gearshifts that were up to 35 per cent faster;
• Had an ‘M’ mode that enabled the driver to perform gearshifts via buttons on the steering wheel and would stay in the gear selected (even when maximum engine speed was reached);
• Had a downshift braking function if deceleration conditions were satisfied;
• Would stay in the current gear if a certain level of lateral acceleration was present (intended to delay or prevent gearshifts when cornering); and,
• Had an optimum gear function – selected by moving the gearshift lever to the left – which would cause the transmission to select the gear for maximum acceleration (depending on current speed and engine management data).

The AMG Speedshift 7G-Tronic also had a torque converter lock-up function above first gear to reduce torque converter slip and increase fuel efficiency. [su_table responsive=”yes”]

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Dimensions and body

Compared to its R170 SLK 32 AMG predecessor, the R171 SLK 55 AMG was 77 mm longer (at 4087 mm), 82 mm wider (1794 mm), 1 mm taller (1271 mm) and had a 30 mm longer wheelbase (2430 mm); kerb weight increased by 45 kg to 1540 kg. Furthermore, the increased use of high-tensile steel contributed to a 46 per cent increase in static torsional rigidity with the roof down and a 19 per cent increase in static bending rigidity.

Relative to the standard R171 SLK-Class , the SLK 55 AMG could be identified by its AMG body-styling which included the front apron and boot lip spoiler, darkened tail-lights and bonnet gills. Furthermore, the SLK 55 AMG’s spoiler lip on the boot lid reduced the lift acting on the rear axle by up to 36 per cent.

Suspension

The Mercedes R171 SLK 55 AMG had three-link front suspension with MacPherson struts, double-tube gas-filled shock absorbers, coil springs and an anti-roll bar. The independent, multi-link rear suspension utilised single-tube gas-filled shock absorbers, coil springs and an anti-roll bar.

Steering

The Mercedes R171 SLK 55 AMG had rack-and-pinion steering with speed-sensitive power assistance (Mercedes-Benz’s ‘parameter steering’).

Safety equipment

Standard safety equipment for the Mercedes SLK 55 AMG included dual front airbags (with two-stage deployment), front seat-mounted side airbags with head and thorax protection, ABS, electronic brake force distribution, brake assist, electronic stability control, traction control, automatically deploying rollover bars and front seatbelts with pre-tensioners and two-stage force limiters.

Brakes

The Mercedes R171 SLK 55 AMG had 340 mm by 32 mm internally ventilated, composite front brake discs with six-piston callipers and 330 mm by 26 mm solid rear discs with four-piston callipers.

Features: Mercedes SLK 55 AMG

Standard features for the Mercedes SLK 55 AMG included 18-inch AMG alloy wheels with 225/40 R18 front and 245/35 R18 rear tyres, an ‘Audio 20’ sound system with a six-disc CD changer, Mercedes-Benz’s COMAND APS (Cockpit Management and Data System) with a 6.5-inch TFT colour screen, DVD-based satellite navigation and a six-disc CD player, dual-zone climate control air conditioning (‘Thermotronic’), contoured AMG sports seats with power adjustment and heating functions, Nappa leather upholstery, cruise control, bi-xenon headlights, front and rear fog lamps, automatic headlights, rain-sensing wipers, an AMG sports steering wheel, remote central locking, power adjustable mirrors with heating and folding functions, power windows, a power adjustable steering column (for height and reach), AMG instrument cluster, a trip computer, wind deflector and an immobiliser.

Extra-cost options for the SLK 55 AMG included ‘Airscarf’ neck-level heating, tyre pressure monitoring, designo leather appointments and fine-wood trims.

August 2007 update

From August 2007, the Mercedes SLK 55 AMG was equipped with a Harman/Kardon Logic7 surround sound system, rear parking sensors (‘Parktronic’) and a motion-sensing alarm.

Related links

• Press Kit: Mercedes-Benz R171.I SLK-Class (March 2004)
• Brochure: Mercedes R171 SLK 55 AMG Black (International) (May 2006)

Review: Mercedes R171.II SLK 55 AMG (2008-11)

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Overview

Released in Australia in June 2008, the Mercedes R171 Series II (R171.II) SLK 55 AMG introduced a new steering system and upgraded transmission. Visually, the R171.II SLK 55 AMG could be identified by its new projection beam headlights with dark surrounds, new front apron with a more pronounced V-shape, black-painted transverse fin and side air outlets, repositioned front fog lamps with chrome surrounds, and larger door mirrors with arrow-shaped LED indicators. Inside, there was a new instrument cluster and NTG 2.5 generation of audio and telematics componentry.

For the R171.II SLK 55 AMG, ‘parameter steering’ was replaced by Mercedes-Benz’s ‘Direct Steering’ which combined speed-sensitive power assistance with variable ratios. As such, the new steering rack adjusted the steering gear ratio with the steering angle, reducing the number of turns lock-to-lock by around 25 per cent.

The AMG Speedshift 7G-Tronic was upgraded and featured aluminium steering wheel gearshift paddles rather than the gearshift buttons of its predecessor. Furthermore, the driver could select from three drive programs:

• Comfort, ‘C’, for softer throttle response, smooth gearshifts and early upshifts to minimise fuel consumption;
• Sport, ‘S’, for greater throttle response, higher engine speeds before upshifting and gearshifts that were around 10 per cent faster than in Comfort; and,
• Manual, ‘M’, for gearshifts solely via the paddles.

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Features

Compared to its R171.I predecessor, standard features for the Mercedes R171.II SLK 55 AMG were extended to include a 500 watt Harman/Kardon Logic7 surround sound system with eleven speakers (including subwoofer), MP3/WMA/AAC compatibility, auxiliary inputs (3.5 mm/USB/iPod/SD card), hard-drive based navigation and 4 GB audio storage, Bluetooth connectivity, voice recognition (‘Linguatronic’) and ‘Airscarf’ neck level heating.

Brochures and downloads

• Specifications and Prices: Mercedes-Benz R171.II SLK-Class (May 2008)
• Brochure: Mercedes-Benz R171.II SLK-Class (April 2011)

Related links

• Wikipedia.org: Mercedes-Benz R171 SLK-Class