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From the sublime to the sensible

After topping the range with the latest M3 convertible, BMW kicks it off with a new entry-level 3-series diesel convertible.

Sometimes life can be cruel. Of the two new guises of the 3-series convertible (one a 420bhp Porsche slayer, the other a 53mpg goody-two-shoes), I naturally got thrown the keys to the diesel. It’s a bit like going on a double date and ending the night palmed off with the ugly best mate. Still, perhaps that’s no bad thing – BMW’s diesel engines are about as revered as they come. Their twin-turbocharged 2.0-litre diesel, found under the bonnet of the 123d, was recently named ‘Best new engine of 2008’ at the International Engine of the Year awards.

It’s a version of that acclaimed engine that powers the new entry level 320d convertible. Notwithstanding the loss of a turbocharger, the four-pot 2.0-litre diesel still produces a healthy 177bhp and 258 lb ft of torque, figures which make it just about acceptable to slot into the curvaceous shape of the 3-series convertible.

Not long ago, the thought of putting a small diesel engine into a svelte open top car would have been anathema, but with this model BMW are wisely responding to their customers’ desire for style without a guilty conscience. And even though the 3-series convertible has now been with us for a couple of years, it still has style aplenty.

Roof up, it is virtually indistinguishable from the 3-series coupe, meaning it’s well-proportioned, subtly sporting and very desirable. Hit the button to take the hard-top roof down (a task despatched in 22 seconds) and you’re left with quite possibly the best looking BMW of the current generation. Opt for the M-Sport spec (as per our test car), and it will even do a passable impression of the M3 with a well-judged body kit, smart 18” alloys and a smattering of M badges.

Slip behind the wheel, hit the ‘Start’ button to rouse the engine and despite what you’re eyes have just told you, it’s clearly no M3 – the expected exotic V8 burble is replaced by a familiar diesel clatter. However, once underway, the engine is impressively smooth, quiet and refined. Unusually for a diesel, there’s also decent throttle response and little noticeable turbo lag.

This effortless refinement combines well with this car’s nature. The driving position is spot on – typically clear BMW dials, neat, simple controls and supremely supportive seats. Despite big alloys, run-flat tyres and what you may have read elsewhere, the ride is controlled and comfortable. The old convertible affliction of scuttle shake (or body flexing for the less technically minded) is almost entirely absent too.

The car also benefits from BMW’s Efficient Dynamics package, consisting of brake energy regeneration and an intelligent alternator (that collects energy to charge the battery) plus auto stop-start. It’s this last feature that makes the most noticeable difference – the moment the car is stationary and in neutral, the engine cuts out. Traffic lights and junctions can be enjoyed in total silence, further enhancing refinement. More importantly, it also enhances fuel economy, the 320d convertible returning an impressive average of 53.3mpg and a lowly 140g of CO2 per kilometre.

So far, so very sensible. But the 320d convertible is more than capable of entertaining. At 1730kg it’s clearly no featherweight, but can still get to sixty in 8.6 seconds and go on to a maximum of 139mph. Respectable enough, but in everyday driving, it feels even quicker than that with a big, flat torque curve making decent progress reasonably effortless.

Find a suitably twisty road, and the car comes alive with fluid, entertaining handling. That heavy folding hard-top doesn’t upset the car’s perfect balance, allowing you to press-on with confidence. Indeed, while the extra weight can be felt, it’s still almost as nimble, roll-free and controlled as a regular 3-series coupe. The whole experience is aided by precise, communicative steering and strong brakes.

The few black marks are more psychological than empirical – driving enthusiastically you need to adapt to the much lower rev limit of the diesel, otherwise you find yourself running out of power and hitting the limiter. And refined as it is, the engine doesn’t sound anything like as nice as the 2.5 six-cylinder unit that can be had for similar money. In a convertible, that could be a deal breaker.

Perhaps that misses the point though. Barring a sexy soundtrack and a few more thousand rpm, the 320d convertible is just as fast in everyday driving as the equivalent petrol, with the same attributes of honed dynamics and great looks. It’s not a bargain basement entry level model at £33,110 for the SE and £35,735 for the M-Sport model, but it is well-equipped and exceptionally capable. Sensible just got sexy.

Verdict

FOR: M3-esque looks, great dynamics, surprising economy and sitting smugly at traffic lights
AGAINST: Not the most tuneful engine
CONCLUSION: The greenest way to enjoy premium open-top motoring this summer

Spec

ENGINE: 2.0-litre diesel
Co2 (g/km)/tax: 140
POWER: 177bhp
TORQUE (lb/ft): 258lb ft
0-60mph (sec): 8.6
TOP SPEED: 139
MPG: -/-/53.3 (urban/extra-urban/combined)
TRANSMISSION: 6-speed
PRICE: £33,110