The sporty versions of the BMW 3 series now get their own label โ€“ 4 series, mirroring the split between the 5 and 6 series. Indeed just like the 6, the 4 is available in coupe, convertible and Gran Coupe guises. Following on from our initial impressions, we've had time to get acquainted with the two-door coupe in what will likely be the most popular variant โ€“ the BMW 420d M Sport.

The transformation from saloon to coupe is executed well, with a purposeful stance and a level of elegance that the bulky Audi A5 can't hope to match. Open the long, pillarless door of the BMW 420d and you are greeted with the familiar but tidy cabin from the 3 series. It's very smart to look at, but some switches feel cheap when used, not in keeping with a list price north of ยฃ40,000.

What does match the price tag is the optional 8.8" multimedia display โ€“ it is impressively crisp and doesn't appear quite as tacked on afterwards ร  la Mercedes. The iDrive system is slick, although some functions can be a chore to find. The sat-nav works well, but rendering your chosen route as a white line over white roads can make it hard to discern where you're going at times. Access to the rear, with strictly two seats, can be a little tight but once in there is adequate head and legroom; if you need to take more than one passenger regularly the Gran Coupe would be a better proposition.

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Up front, the two-litre 4-cylinder turbo-diesel outputs 181 bhp, with a 380Nm plateau of torque served up between 1750 and 2750 rpm. From rest, 60mph can be attained in a claimed 7.3 seconds. Curiously BMW quote the same time for both the two- and four-wheel drive versions. The car we have is fitted with the optional xDrive four-wheel drive system and the sport auto transmission. The ZF 8-speed unit is fast and smooth, and comes with a button that lets you chose from four transmission modes, which greatly alter the character of the car.

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Eco Pro and Comfort modes kill the throttle response, so are best for relaxed cruising. The gearbox smoothly shuffles up to the highest ratio as quickly as it can. Even modest demands for torque are met with boomy grumbling and a deep reluctance to kick down. The coasting mode can feel odd โ€“ release the throttle and there is minimal loss of speed as the drivetrain disengages. This forces you to reach for the over-assisted brake pedal when you'd normally let the engine braking bleed off a few mph, which disrupts smooth progress in light traffic.

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If you need to be decisive it's best to get out of Comfort mode โ€“ engage Sport and the gearbox keeps the engine in the heart of the torque band, giving much keener responses. The turbocharged unit provides strong in-gear performance without notable lag. Sport+ slackens off the stability control and the gearbox holds onto each gear until the bitter end, or when you use the small, too-chunky paddles for a quick upshift. With the BMW 420d all is said and done by 4000rpm, despite the redline being a further 1500rpm around the dial. There is no pleasure to be had extending the power unit โ€“ it feels reluctant to rev, and whilst quiet when cruising, when pressed it emits a harsh, industrial note that is too noisy; the volume could only be forgiven if there was a silky six-pot soundtrack.

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The BMW 420d cruises effortlessly and efficiently. BMW claim 60mpg combined for the 420d. We noted 52mpg average from a tank, evenly split between motorway, urban and B roads, with no concession to driving economically. When not rudely interrupted by the engine the level of refinement is astounding โ€“ wind noise is impressively controlled, almost absent entirely. This leaves occasionally intrusive tyre noise from the optional 19" wheels. Both aesthetically and functionally 18" are a better choice. Expansion joints give a notable hollow thump, and the stiff ride can be fidgety on all but the smoothest of surfaces. Vision to the rear is appalling, so you rely heavily on the parking sensors and door mirrors when maneuvering.

You can carve through bends calmly and accurately with little roll; the chassis is largely unflustered by mid-corner bumps. Despite the apparent stiffness, the suspension copes remarkably well with imperfections in the road surface. The occasional larger defect sends a disconcerting shudder through the cabin. The over-riding impression is a lack of wheel travel, as a result it never feels quite keyed into the surface, but resolutely stable and secure. Traction is impeachable as might be expected with four-wheel drive, which will make the car very usable in poor weather conditions, although wide summer tyres won't help.

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Pick up the pace and unfortunately the BMW 420d does not engage or excite, merely offering aloof competence, even using Sport+. The thick-rimmed steering wheel is smooth and light in use but utterly devoid of feedback. Both brakes and engine offer a lot of response initially, but dig deeper and frustratingly there is little more to be had. A minor tendency to initially push on is perhaps due to the xDrive system. Feed in the power and there's no mistaking it's primarily rear-driven, but the feedback from the chassis feels muted by an over-abundance of grip. The impression is of needing suicidal speeds on public roads to find any reward for driving spiritedly. Perhaps a more powerful engine without xDrive will bring the chassis' character to the surface.

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The BMW 420d is an accomplished mini grand tourer, but falls well short of being a sports car โ€“ consider it a junior 6 series rather than a sporting 3 series. The price makes it harder to justify still, especially given a few choice options inflate it rapidly. Whilst its natural rival is the Mercedes-Benz C-class coupe, an E250 CDI AMG Sport can be had for the similar money. If you simply want an elegant mile muncher, the E class makes the 420d appear very poor value for money. If you can forgo the impressive economy of the two-litre, a smoother, beefier six-cylinder unit will be a much better match to the car's sporting aspirations. The BMW 420d is a lovely car on the surface, pleasurable and easy to use and own, but it lacks depth, and sadly fails to involve the keen driver.

By Martyn Banham @ Road Magazine

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