Sharper than its predecessor and echoing the bold style of its 4 Series Coupe showroom stablemate, BMW's second generation 4 Series Convertible aims to blend sporting driving pleasure and open-air thrills to continue the 35-year legacy in this model class that began with the Munich maker's first 3 Series Convertible.
As before, it sizes up to the same two segment arch-rivals, Audi's A5 Convertible and the Mercedes C-Class Cabriolet - and does so now more directly thanks to the adoption of a fabric roof. And plenty of changes under the skin aim to make it a bit more of a driver's car than before.
BMW has worked hard to ensure that this 4 Series Convertible's handling is as close to that of the equivalent Coupe as possible, using extra bracing and special panels to improve body rigidity, which the company says is 4% better than the previous generation metal-topped model. As usual with this model range, there's rear wheel drive and xDrive 4WD for the fastest models (though this AWD system isn't available with lesser engines as it is on the Coupe). Plus there's a freshly developed double-jointed spring-strut front suspension and a 5-link rear axle.
Engine-wise, the key news is introduction of 48V mild hybrid tech for the 2.0-litre 184hp diesel engine in the volume 420d. The same mild hybrid tech also features with the six cylinder diesels, the 430d (286hp) and the M440d (340hp). And it's on the quickest mainstream conventional petrol variant too, the six cylinder 374hp M440i xDrive, which features BMW's Sport differential, with electronically-controlled, fully-variable locking function in the rear differential, all of this helping to get the power down through the turns, should you want to drive this car in the kind of enthusiastic manner a likely owner hardly ever would. If you do want the ultimate fast version of this car, you'll be directed to the top M4 Competition M xDrive Convertible model, which has 510hp and gets to 62mph in just 3.7s. Toupees will need to be very firmly tied down.
Back in the real world, two conventional 2.0-litre petrol turbo 4 Series Convertible models also feature, the 420i (184hp) and the 430i (258hp). All the engines link up as standard with eight-speed Steptronic auto transmission, which can now be specified with a new optional Sprint function.
Design and Build
No doubt about the main talking point here. The rather inevitable switch from the previous model's metal hard top roof to the same kind of folding fabric top that rivals Audi and Mercedes offer. That means a 40% reduction in roof weight from a soft top that uses panel bow elements and a glass rear window for optimum acoustic and thermal comfort. The electric folding roof takes 18 seconds to open or close and can be used at speeds of up to 31mph. Otherwise, as with the Coupe version of this model, the key change is the adoption of a more vertical upright kidney grille, intended to reference classic BMWs like the pre-war 328 sports car. It's a move that's evoked a mixed reaction from brand loyalists, but as Design chief Domagoj Dukec points out, until the 1980s, the grille is on BMWs were always more vertical than horizontal.
Inside, the cabin follows some of the latest BMW design trends, with a revised dash layout including a smarter drive selector and a start button in the centre console. The 'BMW Live Cockpit Professional' dash set-up is standard, offering a fully digital screen layout that gives you a high-resolution 12.3-inch instrument cluster behind the steering wheel and a 10.25-inch iDrive infotainment Central Control Display. There are also re-designed sports seats and the option of a re-designed head-up display. As before, this is billed as a 'proper four-seater', though the rear seat isn't as comfortable as in the Coupe. Predictably, there's not as much boot space either, the Coupe variant's 440-litre capacity figure falling to 385-litres with the roof closed and 300-litres with the top down.
Market and Model
Sporty 'M Sport' trim is standardised this time round and prices start from around £46,000 for the entry-level 420i, which means a big price premium of almost £6,000 over the equivalent Coupe model. There's a further premium of around £2,200 if you want the 420d diesel version. You're looking at around £50,000 for a 430i. And think in terms of around £60,000 if you want the M440i xDrive model. The top M4 Competition Convertible M xDrive model is around £82,000.
Across the range as an option, there's an 'M Sport Pro' package which includes a special 'Sprint' function for additional bursts of speed and a sporty engine soundtrack in the cabin when the 'SPORT' driving mode is activated. Plus you get M sport brakes, 19-inch 'M light' alloy wheels, a rear spoiler in a high-gloss black, BMW individual high-gloss 'Shadowline' trim with extended features and BMW individual lights and M seat belts. You might also be interested in a browse through the M Performance Parts portfolio, from which you can order things like 20-inch M Performance forged light alloy wheels in a Y-spoke design with a Jet Black matt finish. Or maybe a carbon fibre finish for the front grille, front splitter and side skirts, as well as aero flicks for the front apron in high-gloss black.
Cost of Ownership
Mild hybrid technology has been included with all diesel engines and with the straight-six petrol unit of the flagship BMW M440i xDrive Convertible. Fitting a 48V starter-generator and second battery greatly increases the scope for utilising Brake Energy Regeneration and the electrical power it produces. The recuperated energy collected by the 48V battery can be supplied to the 12V electrical system or used for generating additional drive power when fed back to the 48V starter-generator. When the car is accelerating, the generator is also able to offer the driver an electric boost effect that instantly makes an extra 11hp available.
All of which should promise a very competitive set of efficiency stats. Let's see. We'll start with the petrol models. The 420i manages up to 49.6mpg on the combined cycle and up to 131g/km of CO2. For the 430i version, the figures are up to 47.1mpg and up to 138g/km. For the M440i xDrive, the figures are up to 40.9mpg and up to 159g/km. What about the diesels? For the 420d, the official figures are up 67.3mpg and up to 111g/km. For the 430d, it's up to 50.4mpg and up to 147g/km. For the M440d xDrive, it's up to 44.8mpg and 165g/km. Finally for the M4 version, it's 27.7mpg and 231g/km.