Mercedes-Benz SLK/SLC-class (R172)

	Mercedes SLK / SLC (R172)
	Debut: 2011 Maker: Mercedes-Benz Predecessor: SLK (R171)

Published on 16 Mar 2011

From this angle, the new SLK looks like a mini-SLS, doesn't it ?

Resembling the flagship supercar, the prominent vertical grille is the highlight of its new design. It makes the bonnet look even longer, but is it as distinctive as the old car's F1 nose ? I don't think so.

Elsewhere, the new Sport Light Kompact is rather predictable. Like the last two generations (R170 and R171), it employs a two-piece retractable metal roof, something the original car pioneered in 1996. Also like before, the car is built on a shortened C-class platform, sharing much the same suspensions, steering and powertrains. Even the proportion of the car is barely altered – just 31 mm longer and 33 mm wider, whereas the most important dimension, i.e. wheelbase, is unchanged at 2430 mm. Surprise is the last word to describe the R172.

However, Mercedes found plenty of areas to improve. The new body is more wind-cheating, with Cd 0.30 instead of the previous 0.32. The chassis is more rigid, thanks to using higher percentage of high-strength steel and an additional cross member behind the cockpit. Weight gain is kept to a few dozen kilograms by employing aluminum bonnet, front fenders and chassis cross members, whereas the roof frame is made of magnesium.

The roof itself is also an important upgrade. Not only its operation is quicker, taking 20 seconds instead of the previous 22 seconds, now you can choose among a standard metal roof, a panoramic glass roof or a variable darkness glass roof. The latter employs electrochromic technology first seen on the 2005 Ferrari 575M Superamerica to adjust the level of transparency by application of electric current. It looks really classy.

Thanks to the added width, the cabin offers slightly more elbow room than the outgoing car. The upright dashboard is a reminiscent of SLS, sharing the same classical theme. It's not up to everyone's taste though. Build quality is improved again, thanks to higher grade plastics, chromed vents and gauges and brushed aluminum trim covering the center console. A pity the plastic surfaces are not leather clad, otherwise it could have been more special. Cost is still a constraint in this class.

Wind management is close to flawless. Turbulence can be reduced by the new "Airguide" device, which features two transparent wind stoppers normally rest behind the rollover protection bars. Like SL, the car can be equipped with Airscarf seats, which blow warm air to the occupant's neck so to make open air motoring possible even in winter. This feature is still unique to Mercedes' cabriolet.

As expected, the new SLK is greener and more frugal to run. All petrol engines get direct injection and automatic stop-start function to save fuel. The SLK350, for example, consumes 23 percent less fuel than the outgoing car on European combined cycle. That is a respectable improvement considering the car is slightly heavier and its engine remains normally aspirated. I suppose you know the 3.5-liter V6 is a new 60-degree unit, versus the previous 90-degree V6. The optimum angle not only allows it to run smoother but also saves the need for a balancer shaft, hence saving energy. Output stays the same, but it offers slightly more torque to give you more flexibility.

However, Mercedes' 3.5-liter V6 is no match to BMW's turbocharged 3.0 straight-six in every way. A more sensible choice is the 204hp 1.8-liter DI turbo four on SLK250. It gives up little performance in real world thanks to a wider torque band, which flats out at 229 lbft from 2000 to 4300 rpm. Now it is also available with the 7G-Tronic gearbox (instead of the previous 5-speeder) like the V6, so there is no more excuse to overlook it. The turbo four suits the SLK very well, combining perky performance and a satisfying blend of smoothness and sound quality. It is a night-and-day difference from the unrefined Kompressor engine we remember.

Moreover, the 1.8 turbo is 40 kilograms lighter than the V6. This relieves its front axle and leads to a slightly more agile handling. Speaking of handling, the new SLK is better than the old car as well as its most obvious rivals, i.e. BMW Z4 and Audi TT Roadster. Its steering, whose assistance remains electro-hydraulic, delivers relatively faithful feel in your hands, and its 2.2 turns lock to lock is much quicker than before. Mechanical variable ratio rack makes it handy to drive in the twisty. Its chassis is quite stiff and quite well balanced. There is good amount of front-end bite to resist understeer (less so on the SLK350). Braking is strong, as you would expect on a German car.

That said, the SLK is still some way behind Porsche Boxster for driving fun. Despite of its improvement, it is still not a thoroughbred sports car like the Porsche. The Boxster's chassis is lighter, lower, better balanced hence more agile. Its steering is keener and more tactile. Its gearbox is better than the 6-speed manual of Mercedes, let alone the slightly foolish 7G-Tronic, which makes wrong decisions at times. The boxer engine is more inspiring to rev than either engines on the SLK. Throttle response is also sharper.

That is not much of a surprise, however. The SLK has always been a style and luxury-oriented roadster. Its target customers are likely to be more matured and prefer to drive in relax mood. The new SLK should satisfy them better than ever, because it offers the choice of electronic adaptive damping (beside the standard suspension and sport suspension). It gives the car a surprisingly supple ride on highway cruising. That is also what the car does best. At steady cruising, the engine is quiet, road noise is well suppressed, wind is well contained and the clever dampers take care of expansion joints. The SLK starts looking like a mini-SL. It is truly a relaxing place to be in.

Groundbreaking it may not be, the R172 is the most accomplished SLK among the three generations. It is sportier yet more relaxing to drive. It won't threaten Boxster or Elise in the eyes of keen drivers, but I am sure most other people will prefer its broader talent. Sales figures in the next six or seven years will show.

Verdict:

Published on 12 Dec 2011

SLK55 AMG

The big news on SLK55 AMG is the first appearance of Mercedes M152 engine. This 5461cc V8 is the naturally aspirated version of the M157 serving CLS63, E63 and S63 and CL63. Compare with the old car's 3-valve V8, it is far more advanced, featuring DOHC four valves per cylinder, direct injection and dual-variable valve timing to produce some 422 horsepower at 6800 rpm, or 62 hp more than old unit. Its maximum torque also trumps the old engine by 22 pound-foot. With the new engine, 0-60 mph is shortened by a couple of tenths to 4.5 seconds.

We are not a bit surprised about the performance gain. After all, this is what we should expect for a small roadster powered by a large V8. What really surprises us is how green it is simultaneously. The M152 employs on-demand oil and water pumps, automatic stop-start, regenerative starter-alternator and, most special of all, a cylinder shut off system. The latter uses special hydraulic tappets on cylinder 2, 3, 5 and 8 that provide two lock positions – one for normal valve actuation and another for disabling the valves. Under light load (below 3600 rpm) and with "Controlled Efficiency" mode selected, the V8 is effectively turned into a four-cylinder engine. Consequently, SLK55 achieves an EU CO2 emission rating of 195 g/km and a combined fuel consumption of 33.6 mpg - both are 30 percent better than before. In fact, Mercedes said this is the world's cleanest V8.

Better still, the green technologies do not compromise subjective quality. Thanks to a new variable exhaust, the V8 produces beautiful sound. You will also praise its smoothness and sharp throttle response, which is noticeably quicker than the turbocharged M157. The abundance of torque means the relatively slow 7G-Tronic transmission is hardly a problem in the real world. DCT is just not necessary.

Less remarkable is handling and ride. The SLK55 has always been a compromised package, blame to the short wheelbase and a big engine hanging over its nose. The new car is no exception. It takes a stiff suspension setup to contain its body motion, yet you still sense too much pitch under hard braking or riding over undulations, and a livelier rear end when push hard in the twisty. On less than smooth surfaces, the ride is quite harsh, lacking the beautiful absorption and poise of Jaguar XK. On the other hand, the electric power steering is numb and its assistance inconsistent. The chassis offers neither the precision nor communication like Porsche Boxster or Jaguar. Therefore, the SLK55 works better as a high-speed tourer than a sports car. Its highlight is still very much the V8. This is the greenest hot-rod in the world.

Verdict:

Published on 23 May 2016

SLC-class and SLC43 AMG

In the late 1990s, few things could be as cool as driving a Mercedes SLK and demonstrating the operation of its robotic roof. The little roadster offered plenty of style and reasonable performance. It looked like a mini-SL yet costing just a fraction. It fulfilled the dreams of many who wanted to own a sports car with Mercedes badge. At its peak, Mercedes shifted as many as 55,000 SLKs a year, and more than 300,000 copies over the entire life of the first generation. However, as roadster fever cools down, the SLK is no longer a hot seller. Today, many people see it an overdue fashion, certainly not as desirable as a premium compact SUV. Some roadsters, like Porsche Boxster or Mazda MX-5, can still capture hearts with superior handling and driver engagement, but the SLK, like BMW Z4, just can’t, as they are short of driver appeal.

Mercedes is not going to throw in the towel yet. At the 5th birthday of the third generation SLK, it gave the car a facelift and a new name, SLC. You might remember what the name SLC used to represent – it was the hardtop coupe version of SL. Forget that, the new SLC has nothing to do with that car. It just follows the company’s new nomenclature in which the last letter refers to the mainstream model (C-class) with which it shares platform. Just don’t ask me whether the next SL will be renamed to SLS. I hope not.

New name aside, I found the changes made to the car are just business as usual – yes, those typical styling tweaks, updated powertrains, suspension retune and equipment upgrade. They are certainly hopeless to reverse the sales decline, but should help the car to soldier on for a couple more years.

Despite of the new shape headlights and bumper, the SLC is still hardly a beauty, nor it as characterful as an Audi TT. Its wrong proportion remains, with a bonnet too long, a tail too short, a waist line too high and a glasshouse too small. I guess not even Marcello Gandini could have overcome its packaging constraints.

Part of these constraints is not necessary, such as the large engine compartment. It used to accommodate a 5.5-liter AMG V8 in the SLK55. Introduced in late 2011, that V8 takes an early retirement plan under the pressure of management. Taking its vacancy is a cheaper 3-liter twin-turbo V6 that you can find in many other “semi-AMG” models. It comes straight from the Mercedes production line thus is not hand-built at ‎Affalterbach. 367 horsepower is no match with the old motor’s 422 hp, but expectedly, peak torque is close enough – 382 versus 398 lbft – and it is delivered at lower rev, from 2000 to 4200 rpm. Further helped by adopting the new 9G-tronic gearbox, the resultant SLC43 trails its predecessor by only a tenth to 60 mph, now taking 4.5 seconds. However, the switch from V8 to V6 turbo does not boost as much green credential as imagined. CO2 emission drops slightly from 195 to 178g per km. After all, the V8 had cylinder deactivation.

Mercedes is pretty expert at tuning the exhaust sound of turbocharged engines (as seen in the 5.5 V8 turbo and 4.0 V8 turbo). No wonder the V6 produces a pretty exciting howl above 4000 rpm and angry crackles on the overrun. It can’t quite match the old naturally aspirated V8 though – nothing in the turbocharged world could. The V6 is also strong and smooth, if reluctant to rev beyond 6000 rpm. The 9-speed automatic responds quickly to upshift but hesitates to downshift. Overall, the powertrain combo is effective without feeling as exciting as a true AMG product should.

That said, the SLC43 is benefited by a lighter nose thus it is slightly more agile than the SLK55. The retuned suspension and stiffer steering knuckles also result in a calmer (but still firm) ride and more precise steering. However, the chassis balance of this car is still below standard. Push harder in the twisty and its dynamics start distorting. The ESP light flashes as it tries to contain oversteer and loss of traction. Mid-corner bumps could shudder its windscreen header and shake the steering wheel. An Audi TT Roadster feels more rigid, more modern. Perhaps it’s time to retire the chassis, not the V8. Even though the SLC43 is considerably cheaper than SLK55 (£46K vs £56K), it deserves little applause.

Lower down the range is better. The £40K SLC300 gets a 245 hp / 273 lbft version of 2.0 turbo four-cylinder, which is about the sweet spot as it rarely overwhelms the chassis. There are also SLC200 (£30K) and SLC250d (£33K), whose relative popularity reminds us even Mercedes needs low prices to sell its cars. Sadly but we have to admit, SUV money is far easier to earn.

Verdict: