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Mercedes CLS pre-production (2017) ride review

Published:10 October 2017

Mercedes CLS pre-production (2017) ride review
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By Keith Adams

Devout classic Citroen enthusiast, walking car encyclopedia, and long-time contributor to CAR

By Keith Adams

Devout classic Citroen enthusiast, walking car encyclopedia, and long-time contributor to CAR

► New CLS ride review
► Six-cylinder engines at launch, better NVH
► On sale early 2018

Six months before the 2018 Mercedes-Benz CLS hits the UK market, CAR has been given a ride in two pre-production prototypes, as well as exclusive access to the engineering team responsible for its testing and development. 

The new car, which is set to go on sale in Q2 2018, after its world debut at next month's LA Auto Show, will go head-to-head with the soon-to-be-replaced Audi A7 and recently updated BMW 6-Series Gran Turismo. Mercedes-Benz promises the new CLS will set new class standards for refinement and dynamics.

As with previous generations of CLS, the 2018 model is based on the E-class's platform, and according to Michael Kelz, engineering chief overseeing the programme, the new will be launched with an exclusively six-cylinder engine line-up, although the brand-new four-cylinder versions will follow later in 2018. 

Full preview guide to the 2017 LA Auto Show

The Mercedes-Benz CLS and the market

The new car enters a shifting market. Although the first two generations of CLS have racked up 350,000 sales since launch in 2003, sales for large saloons and coupes are on the wane. 'The CLS sold strongly for the first two years, but now the GLC is dominating our business; it's selling in huge numbers, with demand exceeding supply. So much so that Valmet in Finland is building additional GLCs for us,' Kelz says. 

But the CLS is designed to be built alongside the E-class saloon and estate on the same line, meaning Mercedes-Benz can adjust production volumes depending on sales without compromising the model's profitability. 

The company would like to sell more, of course – the CLS has always been a cash-cow; it's effectively an E-class derivative sold for S-class money.

What's under the skin?

Despite giving us significant access, Mercedes-Benz hasn't told us the complete story yet. It's in the very final stages of its four-year testing and development programme. So far, the 7000-strong team of engineers have racked up a little over five million miles of testing (both real-world and virtually) using around 200 prototypes and pre-production vehicles. 

Our handful of miles across the Yorkshire Dales really are the culmination of a lot of work – the final test drives. Which might explain why our camouflaged examples feel pretty much finished. 'There are a few details, we don't want photographing yet,' laughs Peter Kolb, overall vehicle tester for the CLS programme. 'You'll like the new touch controls four the infotainment system, and there's a night light show that includes the air vents.'

Kelz confirms that there are some new features heading to the CLS. Despite being based on the E-class architecture, there's plenty of S-class technology fitted, including an upgraded Distronic driver assistance package with push-button overtaking function, and the latest Car-to-X comms and updated Pre-safe.

Does it look the part?

It looks that way. The 2018 Mercedes-Benz CLS is very much an evolution of the previous two generations – so retains frameless side windows, a coupe-like roofline, and tapered rear end. The main evolution for the 2018 car is a shark-nose front end incorporating new multi-beam LED headlights for an impressive 650-metre range.

Mercedes CLS pre-production discussion

Michael Kelz confirmed that the drag coefficient of the CLS is 0.27, which although is someway short of the E-class saloon, it does come with near-zero lift at speed to complement its near-50/50 weight distribution. 'Our biggest challenge in the windtunnel is the rear-end of this car – in order to maintain high-speed stability and low drag, we've had to do a lot of clever stuff underneath. We could have given it a Kamm tail, but it would no longer have been a CLS,' he says.

Although our prototypes were taped up, we saw enough to notice the evolutionary front and rear light clusters, plus a more aggressive front end will set it apart from its predecessors. 

Does it get new engines?

You bet! The power line-up at launch will be the all-new in-line six-cylinder OM656 diesel and M256 petrol. They're based on common tooling, which means production flexibility, should demand for either not meet with expectations. The diesel produces 290bhp (CLS 350 d) and 345bhp (CLS 400 d), while the petrol should produce 370bhp in the CLS 350 and 435bhp in CLS 400 form.

Mercedes CLS pre-production twin

It's an engine that packs some very interesting technology. There's a 48-volt electrical system for the top-of-the-range CLSs, which incorporates both a conventional 12-volt battery and a 48-volt lithium-ion power-pack with 1kWh of capacity. This includes an Integrated Starter Generator (ISG) located between the engine and transmission, and acts as a vibration damper as well as firing-up the stop-start system, and managing the car's coasting programme (yes, it shuts down when coasting downhill).

There's an electrically-powered supercharger mounted on the intake side of the M256 that works in conjunction with the twin-scroll turbocharger as it boosts, filling-in any holes in the power delivery. As it's an electrical system, there's negligible lag – a fact clearly demonstrated by Michael Kelz at every opportunity on our passenger ride. 

The other news is that there will be a new four-cylinder engine, known as the M264, which will go on sale later in 2018, and 4Matic all-wheel drive will be offered 'more extensively'. 

Does all this tech mean that this is a hybrid?

Pretty much. The ISG has enough torque to restart the engine, and will harvest energy to recharge the 48-volt battery. It also can add 25bhp-worth of boost, when the driver plants the throttle. What it can't do is run on pure battery power.

This comes in useful not only for the car's hybrid systems, but also for assisting the supercharger, running the car's air conditioning (even for extended periods with the car switched off), and its coolant pump. This improves mechanical efficiency, and therefore performance. 

Mercedes CLS pre-production interior

Under the bonnet, the engine bay is divided into hot and cold sides. As Kelz takes great pains to demonstrate, it's a logical way of packaging the power unit's ancillaries in such a tight engine bay. The hot, or exhaust, side packs the turbo with electrically-operated wastegate, while the electric supercharger and other accessories go on the cool side.

What we do know is that the new inline sixes are almost as powerful as their 4.0-litre V8 counterparts, and are said to be at least a 20% more efficient – fuel consumption and emissions both benefit, although Kelz wouldn't give us specific figures, as the car's not yet been officially benchmarked.

And what's the 2018 Mercedes-Benz CLS like on the road?

We were passengers, so the actual driving impressions will have to wait until the end of the year, but we did get to ride in both the 290bhp diesel and 370bhp petrol models. Starting with the diesel, the first impressions are that it really does nail Mercedes-Benz's brief for class-leading refinement. 

Peter Kolb drove the CLS 350 d, and it's clear that he's intimately familiar with it. 'Can you feel it idling?' he asks. Although there's some background low-frequency noise, you certainly can't feel it. Pulling away, it punches from low revs, with just a muted growl, and cruises exceptionally quietly at UK speeds.

Mercedes CLS pre-production side panning

The main differences between this and the E-class it's based on are the new trims and colours, the new controls for the infotainment system, and the adoption of the recently-facelifted S-class's steering wheel, which houses the cruise control system. 'Customers are happy with this new system over the old column-based one,' Kolb says. We're not so sure.

Our CLS was riding on air suspension which made light work of Yorkshire B-roads. In Comfort mode, ride was cossetting without any perceptible loss of body control. 'The CLS doesn't feel like a large car on these roads,' Kolb says, and looking at his economy of movement at the wheel, this would appear to be the case. Despite the twisting nature of the roads, the Distronic active cruise looked perfectly capable of dealing with the task of following the car behind with minimal driver input.

Would we go for petrol over diesel?

After the brief ride in the CLS 350, we'd probably say yes, if the decision wasn't a purely financial one. Michael Kelz drove us in the petrol-powered car and he was enjoying himself. 'Feel the way it punches in Sport+ mode,' he says as he nails the throttle out of a tight bend. The CLS squats, grips and rushes forward in what feels like an extremely linear wave of creamy power.

Where as the diesel was a muted and refined machine, when allowed to stretch its legs, the petrol CLS is a sportier, more responsive beast. 'The diesel is a great long-distance car,' Kelz says, 'But this petrol version is the best of both worlds – it's refined and smooth when you want to cruise, but accelerates and sounds like a true performance car.'

Mercedes CLS pre-production rear tracking

He wouldn't be drawn on performance figures, confirming with a smile that it would, 'have a maximum speed of 155mph.' But he did then say that the 0-62mph time would be, 'in the low fives.' He also added: 'We haven't needed to enhance the sound of the engine; it's so good. We just had to make sure the driver hears it, not digitally enhance it to sound like something else. It becomes like a video game if you need to do that.'

In Comfort mode its 48-volt system does a very good job of going about its business like a hybrid. It spends much of its time coasting (or 'sailing' as Kelz puts it), and the transition from engine off to engine on is imperceptible from the passenger seat – you only know when by watching the tacho.

What have we learned?

The CLS is an important halo product, and is a Mercedes-Benz mainstay for at least another generation. From the passenger seat, it feels exceptionally refined and in petrol form, promises to be a laugh when you're in Sport+ mode. The biggest question that faces it in the coming months will be the arrival of the next-generation Audi A7. 

Kolb doesn't underestimate the threat it poses: 'it will be impressive, but we think the CLS will be more than good enough to meet the challenge. I look forward to trying it.'

The last word? The CLS's new Energising Comfort control system, which changes the interior ambience of the car depending on your mood. If you want it 'warming', the inside is bathed in orange and red light, while the seat warms and massage you. You can set it to four pre-defined moods, and it'll light, fragrance, heat or cool you accordingly, while tailoring your music accordingly. A gimmick perhaps, but a welcome one for yet another grinding day on the M25…


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  • Mercedes CLS pre-production (2017) ride review
  • Mercedes CLS pre-production (2017) ride review
  • Mercedes CLS pre-production (2017) ride review
  • Mercedes CLS pre-production (2017) ride review
  • Mercedes CLS pre-production (2017) ride review
  • Mercedes CLS pre-production (2017) ride review
  • Mercedes CLS pre-production (2017) ride review

By Keith Adams

Devout classic Citroen enthusiast, walking car encyclopedia, and long-time contributor to CAR