Review of the new Mercedes-Benz E350 CDI Cabriolet

There are two-seater convertibles, there are four-seater convertibles and then there are four-seater convertibles that can actually sit four people. Now, you might think that by definition any car with four seats can seat four, and maybe even five if they're willing to squash up a bit in the back. That is generally the case but when we're talking about convertible cars, the usual criteria for what constitutes a seat seems to go out of the window.

There are all kinds of drop-top vehicles with comical rear seats which no adult could conceivably sit comfortably in without first feeding their lower body through an industrial mangle. The Mercedes-Benz E350 CDI is an exception - a large and not inexpensive convertible that would suit buyers who want to transport fully grown humans in the rear without contravening their human rights.

There's no big deal about diesel convertibles these days. A decade ago, engine technology couldn't quite deliver the refinement that's necessary in a car without a roof, let alone exhaust gasses that were suitably free from unpleasant smog and odours. Today, the E350 CDI Cabriolet is whisper quite at idle and keeps itself very much to itself when on the move. That's despite performance which is brisk but in an effortless way that's befitting of a big Mercedes-Benz convertible.

The 227bhp engine can spirit the E350 CDI cab to 62mph in under seven seconds and brush up against the 155mph speed limiter. It's the combination of the creamy smooth seven speed automatic gearbox and 540Nm of torque which really defines progress in this car though. Prompt the gearbox to kick down and the acceleration pours out. You wouldn't class this as a sporty drive but there's a fine Mercedes-Benz mix of comfort, refinement and straight line speed.

"the E-Class looks like the default choice for those prioritising comfort and style"

Show the E-Class Cabriolet a corner and it holds itself together well for a car of this size without the bracing effect of a fixed roof. It stays flat and has plenty of grip but mid-bend bumps can unsettle the suspension and the occasional shudder is detectable through the steering wheel.

At 4,698mm long and 1,786mm wide, the E-Class Cabriolet is big but still 170mm shorter than the E-Class saloon. To avoid having to lug around a folding metal roof large enough to span its roomy four-seater cabin, the car has stuck with the traditional soft-top but incorporates a series of features designed to enhance passenger comfort. The roof itself takes just 20 seconds to open or close, a fast time for such a large canopy. It can also be operated at speeds of up 24mph to lessen the chance of being caught in that downpour. With the roof down, there's still a 300-litre boot capacity and 90 litres more if you keep it up which is very good for the class.

The roof is extensively insulated against heat and sound to keep occupants comfortable in all weather conditions and even at high speeds. Mercedes claims that it's possible to have a normal phone conversation in the car at 125mph and that you can put the E-Class Cabriolet through an automatic car wash "without hesitation". With only two doors, this long car gains a very sleek shape and the clever Easy-Entry system is incorporated to aid access to the back seats.

The all-weather credentials of the E-Class Cabriolet are further enhanced by its specially designed ventilation system which can incorporate Airscarf and Aircap technology. Airscarf takes the form of vents integrated into the front seat backrests and head restraints which provide a stream of air at the desired temperature to make top-down motoring more comfortable. The Aircap is a wind deflector, a net in the windscreen frame and a draught stop between the seats. These can be deployed at high speeds to deflect air up and over the cabin making progress more comfortable for occupants.

There are more affordable engines in the E-Class Cabriolet line-up but few more desirable than the 3.0-litre diesel in the E350 CDI. Standard equipment includes 17" alloy wheels, front and rear parking sensors, the Aircap wind deflector, electric heated seats, automatic climate control and leather upholstery. An upgrade to Sport trim brings AMG styling accessories and a Sport button which stiffens the suspension and throttle response. Seven airbags are fitted as standard as are seatbelt pretensioners and force limiters.

There aren't too many direct rivals for the E-Class Cabriolet, particularly if you're interested in a convertible with four usable seats. Despite being based on smaller compact executive platforms, the BMW 3-Series Convertible and Audi A5 Cabriolet offer similar amounts of cabin space and the top diesel models are priced at similar levels to the E350 CDI Cabriolet but they're a little sportier in feel. The Infiniti G37 convertible and Lexus IS 250C have a similarly relaxed character but again, space is down on the E-Class and there's no diesel option.

Efficiency has been central to the thinking of the engineers who developed the E-Class Cabriolet and there are a number of fuel-saving measures on-board. These include on-demand activation of the steering and fuel pumps, the use of tyres with low rolling resistance and an alternator control system which takes account of the current driving situation and the vehicle's electrical power requirements. Then you have the car's aerodynamics which with a drag coefficient of 0.28, are outstanding for a convertible the size of the E-Class. The E350 CDI model returns 50mpg with emissions of 148g/km.

There are lots of convertible cars out there and most of them can be obtained for rather less than the £40,000 Mercedes-Benz is asking for its E350 CDI Cabriolet. If a rustle of wind in the hair on a sunny day is the extent of your ambition, then maybe the big Merc does look a trifle pricey. If, however, you're after a genuine four-seat convertible, with effortless performance that's as at home on the Coventry ring road in the rain as it is turning heads on a Cote d'Azur boulevard, the options get a lot more limited.

Not only has Mercedes designed a hugely impressive large convertible, it seems to have endowed it with a mix of abilities that's extremely rare in today's market. With most of its rivals taking a sportier line and offering less space and comfort, the E-Class looks like the default choice for those prioritising comfort and style. The diesel engine in the E350 CDI is a perfect accompaniment to this relaxed approach to convertible motoring.

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