BMW's new 4 Series adds more than just one number, says motoring editor Andy Russell.

The number's up for the BMW 3 Series Coupe as it makes way for a new range – the 4 Series.

The 4 tag also goes on the new convertible as the German manufacturer looks to emphasise these models' even sharper dynamics and exclusivity from the 3 Series. It's a similar story with the new 2 and 1 Series.

Before you dismiss it as just a rebadging exercise, the 4 Series does feel more special than the current 3 Series, and with my son driving the previous 3 Series Coupe we had plenty of chance to compare them.

For a start the 4 Series is slightly longer, wider and lower which not only makes it look sleeker but also gives it the lowest centre of gravity in the current BMW range. A longer wheelbase and wider tracks – the rear wheelarches are the widest point of the body – means it has a bigger footprint and hugs the road even better while offering a little more space inside to make what was already a most practical coupe even more accommodating.

What really set it off are the black air breathers behind the front wheels which look good and help to reduce turbulence and drag so improving the aerodynamics.

Despite the new badge, the 4 Series is evolutionary rather than revolutionary which has worked so well for BMW on other models.

Under the bonnet is a range of tried-and-tested TwinPower Turbo engines – 184hp and 245hp 2.0-litre 420i and 428i and 306hp 3.0-litre 435i petrol and 184hp 2.0-litre 420d and 258hp and 313hp 3.0-litre 430d and 435d – the latter with standard all-wheel xDrive which is also available on 420i and 420d.

The big seller will be the free-revving 420d for its strong punchy performance and a real-world 50-60mpg overall in mixed driving.

The standard six-speed manual gearbox has a short throw but needs a deft, firm action so the excellent, sweet-shifting eight-speed automatic is worth considering.

My SE test car was fitted with the £750 optional adaptive M Sport suspension giving the best of both worlds when it comes to comfort and agility – a world away from my son's teeth-chattering 3 Series M Sport Coupe. And with the wheels pushed out even further to the corners, and a lower ride height and centre of gravity, it sticks to the road through corners even more tenaciously.

The first 3 Series Coupe changed the thinking on coupes – more two-door 'saloon' than cramped 2+2 – which is a big part of the appeal.

The 4 Series seats four adults with decent legroom but tall passengers will find headroom tight in the back. With front seats that tilt and slide forward and long doors, getting in and out is simple while the 445-litre boot is well shaped with good access for large suitcases. For longer loads 60/40 rear seat backs can be released via levers in the boot and lay flat.

The tasteful cabin uses top-notch trim and is pure BMW for style and simplicity of controls with iDrive controlling most functions via the 6.5in free-standing screen which unfortunately looks like an afterthought and, unlike Audis, does not retract into the fascia.

The coupe has always cost more than the saloon but the 4 Series Coupe has more equipment than the model it replaces with standard front and rear parking sensors, heated front seats, multi-function steering wheel, brighter xenon headlights, digital radio, leather seats, two-zone air-conditioning, cruise control, Bluetooth, Drive Performance Control with eco, comfort and sport modes and automatic lights, wipers and boot opening. SE, Sport, Modern, Luxury and M Sport trim levels are offered.

The breakaway 4 Series gives the Coupe more of an air of exclusivity but, with BMW looking to sell 9,000 in the first full year, it will be interesting to see the effect that will have on overall sales of the 3 Series – currently a UK top 10 seller.