The BMW 4 Series Convertible might feature an unfamiliar number but its talents shouldn't come as any surprise. The revised range now features a rejuvenated line-up of petrol powerplants too. Jonathan Crouch reports.
Ten Second Review
BMW's 4 Series Convertible perseveres with a neat metal-folding roof that offers a different option to executive segment cabriolet buyers not already swayed by the competing charms of rival open-topped versions of the Audi A5 and Mercedes E-Class. You won't get the large boot and cutting-edge driving dynamics of the 4 Series Coupe, but compensations come in the form of refinement, security and drop-top desirability. And there's also a rejuvenated range of petrol engines too. In short, you'd like one.
It's the thing that makes a BMW handle like a BMW should. I'm talking of the brand's famous 50:50 weight distribution, something the Munich marque makes possible by the almost unique rear wheel drive configuration it applies to most of its models. But with this car, puts at risk than with any other design in its line-up. Welcome to the 4 Series Convertible. The reason for that is also the main reason why you might buy this car - its metal folding roof. Alone in the executive convertible segment, BMW continues with this arrangement, rather than the soft-top fabric roof mechanisms rivals Audi and Mercedes use. It's a unique touch that'll tempt people liking the security, refinement and pavement wow factor of a folding metal top. But the system weighs a quarter of a tonne and needs complex, heavy mechanicals that must be very carefully positioned to maintain that perfect weight distribution I mentioned at the beginning. Still, the promise with this car is that the German engineers have managed to do just that even more effectively than they did when battling with the same configuration in this model's direct predecessor, the fourth generation 'E90' vintage 3 Series Convertible. And, with a rejuvenated petrol engine line-up added to the range, this car looks a better all-round proposition than it was before. Let's try it.
Is the average BMW 4 Series Convertible customer going to approach this car wanting to sling it around a bit? Provided the variant in question isn't the hot rod M4 model, I suspect not. Which is perhaps just as well, for comfort is higher on this car's priority list than cornering heroics. To be fair, this model is more dynamically inclined than its direct Audi A5 and Mercedes E-Class rivals - you get that classic BMW hunger to turn into bends and lovely front to rear balance, helped by the near 50:50 weight distribution and rear wheel drive. To compete with Audi, BMW's xDrive all-wheel system is even offered at the top of the range. On to engines. Diesel-wise, this means a choice of three units, starting with the 190bhp unit found in the 420d. Above that come the six cylinder diesel models, the 258bhp 430d and the 435d diesel range-topper with a hefty 313bhp at its disposal and xDrive 4WD. The big recent changes with this car though, centre on the petrol engines in the line-up. Not much is different with the base four cylinder 184bhp 2.0-litre unit found in the 420i, though it is slightly more efficient. The pokier version of this powerplant though, previously badged '428i', now carries a '430i' badge and has its power raised from by 10bhp to 252bhp, while torque is up to 350Nm, making possible a rest to 62mph time of just 6.4s. That makes it difficult to imagine why you'd want a six cylinder petrol model, but if you still do, the previous 302bhp 430i model has now been replaced with a 326bhp '440i' variant. Remaining at the top of the range is the twin turbo six cylinder 431bhp M4 performance model. But I haven't yet talked about the roof. If the sun comes out or the heavens open, it's nice that you don't now have to stop at the side of the road to either retract or erect it, though you do have to slow to a speed of below 8mph for the 20 seconds the three metal panels take to assume their necessary positions. When the top is up, the refinement you get is indistinguishable from that you'd expect to find in the 4 Series Coupe model, thanks to a number of design improvements made to this Convertible version. These include a sound-absorbing headliner that reduces wind noise by up to 2dB.
Design and Build
BMW alone persists with the metal-folding roof concept in this segment, so if you prefer this 4 Series Convertible to either of its two direct rivals, Cabriolet versions of the Audi A5 and Mercedes E-Class, that's likely to be the major reason why. Having to create a pretty shape that effortlessly swallows all the roof-work's sliding metal panels must be quite a design challenge but here, that's been expertly carried off, helped by the fact that like all the most modern folding hardtops, the BMW system - which takes 20 seconds to operate and can function at speeds of up to 8mph - uses three rather than two-pieces. The advantage of this is that you don't need a distended rear end on the car to accommodate the larger sections of a two-piece roof. The downside of stacking three rather than two pieces on top of each other in the boot is that when they're all folded and sandwiched together here, there's not a great deal of luggage space left. With the roof up, you'll get 370-litres of cargo capacity. But fold it down and that figure falls to just 220-litres. And the rear seats? Well, getting to them isn't the easiest task in the world and once you're seated, you'll find that the extra 50mm of wheelbase and 26mm of length this car enjoys over its 3 Series Convertible predecessor really tells, freeing up 13mm more stretching room for your lower limbs. At the wheel, there's a low-set driving position and a grippy three-spoke sports steering wheel. Optional on this car is the Air Collar, a concept first pioneered by Mercedes, with vents below the head restraints that can massage your neck with comforting warm air on cold mornings. Otherwise, everything is as it would be in a 4 Series Coupe.
Market and Model
Expect to pay somewhere between £35,000 to £50,000 bracket for mainstream 4 Series Convertible models - though you could pay over £60,000 if you want to consider the desirable M4 flagship variant. If you're comparing against an equivalent 4 Series Coupe with the same engine, that means a drop-top premium of between £4,000 and £5,000, depending on the variant you're looking at. Most customers will be browsing at the bottom of the range where both the 420i and 420d models put out 184bhp and 190bhp respectively but if you choose the diesel version, there's a premium of around £2,500 to find over its petrol equivalent. With all the four cylinder models, you're also looking at about £1,500 more if you want to specify 8-speed automatic transmission many will want. That's standard on the 440i petrol and six cylinder diesel models but then, for the kind of prices these variants command, it probably should be. Equipment includes the power-folding roof of course, plus all variants get the iDrive infotainment system with its 6.5-inch colour screen, automatic xenon headlights with heated washers, front foglights, smart alloy wheels of at least 17-inches in size shod with run-flat tyres, heated door mirrors, an alarm, Park Distance control at the front and the back, rain sensing wipers and a Hill-start Assistant to stop you from drifting backwards on uphill junctions. Inside, there's leather for both the heated electric front seats and the multifunction three-spoke Sports steering wheel, dual zone air conditioning, cruise control, an auto-dimming rear view mirror, a trip computer, Bluetooth 'phone compatibility and a decent quality six-speaker 'BMW Professional' stereo system with a digital radio with USB and Aux-in points. You also get the Drive Performance Control set-up that enables you to tweak steering and throttle response to your mood - though you can get a bit more from that system if you pay extra for the Adaptive suspension.
Cost of Ownership
Can this really be seen as an efficient car? After all, it carries around a very inefficiently heavy roof mechanism. A BMW 320d saloon weighs 1,495kg: this 420d Convertible weighs 1,755kgs. Those are the facts - and they go much of the way towards explaining why metal folding roofs have fallen from favour the in current, efficiency-obsessed automotive design. Having said all of that, the Munich maker is keen to point out just how much effort has gone into minimising the downsides of this approach with this car. The result of a whole range of EfficientDynamics tweaks is that BMW has kept the running cost penalty of opting a 4 Series Convertible over a 4 Series Coupe to around 10%. The manual gearbox 420d Convertible manages 55.4mpg on the combined cycle and 127g/km of CO2. As for pokier 4 Series Convertible diesels, the 430d manages 55.4mpg and 134g/km. Even the top automatic-only 435d xDrive model with its standard 4WD system gives you 47.9mpg and 155g/km. On to petrol power. A 420i Convertible manages 45.6mpg on the combined cycle and 145g/km of CO2 in manual form. With the 430i, you can expect 42.8mpg and 162g/km in manual guise. On that basis, it's hard to justify the six cylinder 440i variant. It goes hardly any faster than a 430i, yet costs far more to run, delivering 41.5mpg and 167g/km. That only leaves the flagship version of this car, the potent 431bhp M4 variant. In its most efficient automatic form, this car can manage 32.5mpg and 203g/km, returns that embarrass those of its most direct rival, Audi's RS5 Cabriolet.
Would this car be a more engaging driving machine without its weighty roof mechanicals? The extra sharpness of its 4 Series Coupe stablemate certainly suggests that. I sense though, that most buyers of this open-topped version will be quite happy with a more relaxed, comfortable demeanour. That is, after all, as much as competitors from Audi and Mercedes offer - and those brands can't deliver the engine choice BMW provides here. In fact, a lot of boxes are ticked by this car if you can afford its asking price. You get impressive safety systems, high residual values, above average rear seat legroom and a sheer depth of engineering that rarely fails to impress. As a result, in many ways, it's probably the most complete contender in this segment and, best of all, it looks as striking and expensive as a convertible of this kind should when the sun's out and all is right with the world. True, there are probably all kinds of ways of more sensibly spending the budget required for one of these. You know what though? Right here, right now, I can't really think of any..