We like
Smooth, powerful and melodic six-cylinder engine, user-friendly convertible roof

Room for improvement
Unexpected rattles and squeaks

FOLLOWING standard practice in the car industry, BMW waited a while before dropping a convertible version of its current E46 3 Series range into the product line-up.

A staggered introduction of a new model is often dictated by factory availability but can also help spread the impact of a new model range.

So the local launch of this third-generation BMW convertible came at a time well suited to soft-top sales - just prior to summer - and coincided with the introduction of a new 3.0-litre, 170kW engine now available in 3 Series sedan and coupe models as well.

This was some 24 months after the Australian public first saw the new 3 Series in sedan form and 15 months after the coupe version was introduced.

The 3 Series convertible comes with the usual assurances of safety and body rigidity BMW says the 10,900 Nm/degree static stiffness is a high level for a four-seat open car.

Safety elements include the provision of dual front air bags as well as side airbags for front and rear passengers, plus pop-out roll bars behind the twin rear-seat headrests. These deploy in an instant if the car is in danger of inverting itself.

The new convertible also comes with fuss-free folding and unfolding. It dispenses with windscreen clips, and goes smoothly through its contortions to open or close in just 25 seconds. And, importantly, the BMW now has a proper glass rear window complete with demisting wires.

The convertible gets much of its panel work from the coupe, with which it chares everything from the windscreen forward. The doors - minus the window frames - are also from the coupe although the boot sits a little lower and has a more clearly defined upper lip.

Sitting on standard 17-inch alloy wheels, the convertible BMW is a nice looker, although perhaps not as distinctively different as the sedan and coupe models from the E36 predecessor.

Like most convertibles it looks best with roof down although the quality and comfort factors are improved markedly simply through the thermally padded roof lining and glass rear window. An optional hardtop can be ordered to create a full coupe atmosphere during the winter months.

Also like most convertibles, the BMW weighs more than either sedan or coupe 3 Series models - exactly 165kg more than the four-door and 155kg more than the two-door.

It is fortunate that the 3.0-litre is standard in the convertible because it keeps performance at respectable levels. The five-speed manual version will see 100km/h coming up in 7.4 seconds while the optional five-speed automatic Steptronic takes 8.1 seconds.

The new 3.0-litre straight six is not the first of this capacity for BMW, but it is undoubtedly more advanced than any of its predecessors of the same size.

It is basically the 2.8-litre BMW six with the bore lengthened from 84mm to 89.6mm - a move which plays a part in lifting power from 142kW to 170kW - and a refined VANOS variable valve timing system that increases intake valve lift and duration.

The torque figure is impressive too, with 300Nm developed at 3500rpm - 90 per cent of which is available from 1500rpm.

Various measures taken with the bigger engine, such as reducing piston friction and lowering idle speed have meant fuel consumption remains the same as the previous, smaller engine. In the manual-transmission convertible, this means a city figure of 10.7 litres/100km and a highway figure of 6.6 litres/100km - excellent figures for a powerful convertible approaching 1.7 tonnes.

The cockpit is essentially the same as sedan and coupe in terms of general layout, except the rear seat holds two passengers only, due to the extra confinement caused by the roof mechanism. Headroom (roof up) is not much different to the sedan, except for a small reduction in the back. Fold the roof and it is infinite.

The boot, like all convertibles, is compromised a little by the need to accommodate the roof, but can be expanded from 260 to 300 litres by folding up the bag that holds the folded roof.

Interior presentation will be entirely familiar to those accustomed to 3 Series BMWs. Leather is dominant on seats and door inserts as well as steering wheel and gearshift, and there is a reasonable amount of wood grain on the dash and centre console to engender feelings of luxury consistent with the price tag.

Front seats are electrically adjusted (and heated) and there's a killer 10-speaker sound system complete with a boot-mounted CD stacker. A park-distance control system is standard to take some of the guesswork out of squeezing into tight spaces.

Climate control air-conditioning is of course part of the deal although a TV monitor is optional - as is BMW's satellite navigation system. The convertible comes ready to accept an integrated mobile phone system.

On top of all this, the 3 Series convertible is nice to drive, too.

Like most four-seat convertibles, the BMW is more comfortable in the role as a boulevard cruiser than a sports car, although it acquits itself pretty well in the latter context.

The 170kW engine has deep reserves of torque, more than its immediate predecessor, and delivers useful response from relatively low engine speeds.

Considering BMWs were once better known for a propensity to rev rather than deliver low-down lugging power, this marks a continuing change in attitude towards BMW engine characteristics.

It also sings a delightful song, slightly hard-edged when wound out towards the (relatively conservative) red line and issuing a deeper, melodic thrum when cruising at lower rpm.

The five-speed Steptronic auto in this case responds better at most times to manual selection as it is a helpful way of dealing with the extra weight.

Manual override allows the driver to anticipate upcoming engine loads and generally avoids the hunting around for correct gear ratios that even a system as sophisticated as the BMW's is occasionally prone to suffer.

Yes, even though the torque factor is favourable, the convertible is a 1.7-tonne conveyance at the end of the day and 3.0 litres is still working relatively hard to overcome it. The difference is that the BMW engine does not mind working hard - in fact it invites it.

The convertible also steers with precision, using the grip of the asymmetric tyre choice (225/45R17 at the front and 245/40R17 at the rear) to generate impressive G-forces before any loss of traction. And then, the stability control system steps in anyway.

The steering felt as responsive and progressive as 3 Series sedans, making the convertible a device to move quickly, safely and enjoyably from point to point should you wish to do so.

And with four-wheel disc brakes working through a four-channel anti-lock system, the car stops with assuredness.

Surprisingly, the test car was not entirely free of the squeaks and rattles common in large soft-tops. Although most of the noise came from relatively superficial areas suggesting body flex was not a major contributor, their very presence was unexpected.

But the convertible BMW is a lovely, easy to live with prestige soft-top that delivers the style, quality, comfort and performance that are the cornerstones of the brand.