Overall rating:

Our second try of BMW's new 4 Series Convertible sees us back home in Europe and testing what will be the biggest-selling model in the UK, the 420d, but there's no escaping our initial conclusion, which is that the F33 is designed to be more of a cruiser than an open-top sports car.

Key Facts

Model tested: BMW 420d SE Convertible
Pricing: £36,675 basic; £43,850 as tested
Engine: 2.0-litre turbocharged four-cylinder diesel
Transmission: six-speed manual, rear-wheel drive
Body style: two-door convertible
Rivals: Audi A5 Cabriolet, Mercedes-Benz E-Class Cabriolet
CO₂ emissions: 138g/km
Combined economy: 53.3mpg
Top speed: 146mph
0-62mph: 8.2 seconds
Power: 184hp at 4,000rpm
Torque: 380Nm from 1,750- to 2,750rpm

In the Metal:

One clear area where the 4 Series (F33) moves the game on from its 3 Series badged predecessor (E93) is in the looks department; it's definitely a tauter and more muscular creation on the outside, with the rear-end treatment working particularly well, while the cabin has also improved immeasurably. It can still look ever so slightly under-wheeled in certain specifications, but it always looks an expensive piece of kit, whether as a 420d SE model or with sparkling Estoril Blue metallic (a classic BMW colour that's been recently revived) clothing the body of a full-on 435i M Sport.

Driving it:

The 420d Convertible is a beautifully restrained operator. In terms of refinement, it has an extraordinary ability to filter out all the major contributors to passenger discord - the engine is inaudible during all but the most extreme throttle applications, the ride is so supple and fluid that it makes you wonder why you'd need a 'proper' GT costing three times as much and with a wind deflector in place, even hood-down motoring is a serene affair.

It's also not slow; the 2.0-litre diesel engine is no firecracker, but it's easily capable of moving the beefy 1,680kg Convertible around, with a slick and well-judged manual gearbox making it a pleasure to elicit acceleration. Initial take-off is a little flat, but the fat mid-range and its willingness to rev to 4,000rpm and beyond make the 420d deceptively fast - more so when you factor in the engine's softly-softly vocal act and the cosseting, languid lollop of the suspension in Comfort mode.

The problems bubble up when the roads are not favourable to such effortless mid-revs pace. The 420d is most happy on great big sweeping routes, with long constant radius corners and smooth surfaces. In this sort of environment it can make indecent progress without ever making its driver sweat, and with the hood down and the sun shining it's hard to think of better cars to recommend if you want to spend three weeks lazily criss-crossing Mediterranean Europe every summer.

Go to seven-tenths and it just about manages to hang together, but the car's bulk now makes its presence felt, while the weighty, but too-vague steering (this is the case even in Sport and Sport+ settings) makes it clear that the limited information you're getting is as much as it will ever reveal to you. Really begin to bully it on tighter roads and the limits of the 420d's dynamic ability are all too obvious. Understeer, faint traces of roll oversteer that even electronics can't restrain and a certain degree of raggedness quickly force you to drop the pace back down, knock it out of Sport+ mode and enjoy the view. Sure, the 3 Series Convertible that the 4 Series supersedes wasn't exactly an M car in sheep's clothing, but we don't remember it feeling as uncomfortable as this did when pushed as hard as possible.

What makes all of the above most surprising is that this 420d SE was fitted with optional M Sport suspension with adjustable dampers (£750) and BMW claims to have preserved the sporty character of its previous convertibles by optimising camber angles, reducing the height of roll centre, giving the 4 Series a wider track and letting it ride 10mm lower than the 3 Series saloon on which it is based. In our opinion, all these good intentions never quite translate to genuine handling capability.

What you get for your Money:

BMW makes big noises about the fact it has added in £1,500 worth of extra standard equipment - one such item being the Air Collar neck heating system in the seats, which is a nice touch - yet prices compared to outgoing 3 Series Convertibles have only risen £375 to £495 across the range. The 4 Series does come pretty well-specified across the board, but there's still the potential to fit all manner of accessories to it, as evinced by 'our' bottom-spec SE, which was loaded up to £150 short of forty-four grand.

Trim levels split above the SE - on the comfort side of things, the Modern is £1,500 more than the SE, with the top-line Luxury another £2,500 on top of that. Try and elicit some sportiness and you can have Sport, again for £1,500 above an SE, with M Sport topping the whole range at £3,000 more again.

Finally, fuel economy - BMW's quoted combined figure of 53.3mpg seems reasonable, given that we hammered the poor 420d hard through the mountains, hood down and two-up, and it still returned an average mpg figure in the high-30s over an 80-mile route. Legal cruising on motorways should therefore easily surpass 50mpg, all things considered.

Worth Noting

On the old 3 Series Convertible, there was a complex arrangement for getting your bags out of the boot with the hood down, which was some sort of arcane puzzle to test your spatial awareness that required moving flaps and pressing key fob buttons (if you'd bothered to specify them) in a certain order. So fiendish a system was this that we distinctly remember the German model specialist on-hand at that car's launch getting flustered as he was unable to make it work in front of a mob of wryly amused hacks.

BMW has addressed such tomfoolery this time around by adding a simple 'up and down' rocker button in the boot lid interior. Press 'up' and the whole rear deck, plus the stowed roof arrangement, lifts straight up in the air - allowing you access to the whole boot, once you've moved the luggage stowage lid out of the way. Take out your bags, press the down half of the button and the Four quickly returns to its driveable, open-roof state. All very clever.

Summary

Three things have happened in the transition from 3 Series Convertible to 4 Series Convertible: it's become better looking inside and out; it has certainly become more refined and luxurious too; but it has lost some of its dynamic edge. You can clearly make the case that anyone buying a four-cylinder diesel convertible is not exactly going to be doing a lot of track days or charging up snaking mountain passes, and for covering a massive amount of ground in style and with a definite feel-good factor, the 420d hits its straps in emphatic fashion. But if you've always appreciated the driver-focused slant that BMW used to engineer into all of its products, no matter how relaxed said model's outlook, it's difficult to see what the 4 Series now offers over and above similar rivals from Audi and Mercedes-Benz, which were historically always lagging behind in the four-seat convertible driving stakes. Whether that bothers you or not will determine if you view the 4 Series as a roaring success or a dynamic near-miss.