SUBTLE is not often a word used in connection with car designers when they are trying to create a new model.

Equally applicable is that old adage of why change a winning formula?

BMW's Bavarian backroom team has managed to achieve both with the latest 4 Series models.

Since the original arrived back in 2013 the replacement for the former 3 Series coupe and convertible has been a huge success.

Britain is key to the 4 Series' fortunes with sales second only to those in the USA. Germany, the car's homeland, languishes in third place.

Last year BMW sold 9,136 4 Series Coupes in Britain, 10,085 four-door Grand Coupes and 4,258 Convertibles.

This year the new models are expected to be even more popular.

BMW's medium sized car UK sales boss James Thompson told me: "The 4 Series has been a huge success for us and interestingly three out of every four we have sold buyers have opted for the M Sport versions whilst the added bonus is that residuals have held up so well and better than any of its rivals.

"The key to this new, updated range is subtlety because on the surface it may not look any different but there are many changes which obviously enhances the model."

Certainly,the styling changes on the new 4 Series models are noticeable with a large air intake at the front flanked by LED headlights while the rear light cluster and back end appearance have also been tidied up.

Crucially all three models now have a lower centre of gravity thanks to a wider track (14mm extra front and 20mm at the back), plus there's a revised suspension and improved traction control capabilities, again all rather subtle but meaningful from a driver‘s viewpoint.

With just three trim levels now offered - SE, Sport or M Sport with the Luxury models now dropped - all models now have new twin LED headlights as standard while the changes to the rear gives the 4 Series a lower and more sporty look with the light clusters certainly emphasising the muscular wheel arches.

Underneath, more subtle changes have been made with the car now having stiffer suspension with better damping and an upgraded steering set-up has helped to deliver better handling and greater straight-line stability.

Inside the new 4 Series subtlety is again the order of the day with several minor new touches to the furnishings, like the surrounds for the air vents and the control panels in the doors which now feature electroplated inserts, while the air conditioning and audio controls now have chrome surrounds.

It's these small and perhaps, to some, insignificant changes that make a difference such as the sports style steering wheel, now fitted as standard across the range. It is of a better quality leather and gives the driver more grip than on the previous line up.

Drivers can also personalise their particular 4 Series model with, for example, a choice of 18-inch or 19-inch light alloy wheels specially made for this range while there are new features on board for the sat nav, telephone connectivity and display screen controls all making life simpler because of their ease of operation.

There's a wide choice of petrol and diesel engines and according to James Thompson the best selling coupe will be the 420d, accounting for almost 30 per cent of sales. That will be followed by the M4 at an expected 17 per cent.

The top Grand Coupe and Convertible models will also have the 420d engine under the bonnet.

So what's the revised 420d like in the Sport Coupe?

In a first drive exercise over some 80 miles it's easy to see why this engine will be the most popular. It's responsive yet so quiet for an oil burner and really provides an impressive driving experience, particularly with such a neat, precise six-speed manual gearbox - there is an eight-speed automatic as an option.

The power comes through with exceptionally good, low down torque from the 2.0-litre 190bhp turbocharged engine and once out on the motorway it's powerful and comfortable making it an ideal long distance cruiser.

With BMW's xDrive all-wheel-drive on board this again makes for easy motoring whatever the road conditions and the official combined fuel consumption is 62.8mpg with a 0 to 62mph acceleration of 7.3 seconds and CO2 levels of 125g/km.

The basic price of the 420d xDrive Sports Coupe is £36,260 but this particular car was loaded with optional extras such as an advanced parking package (reversing camera and park assist) at £545, driver comfort pack (electric front seats, driver memory seats) at £1,440 and a media pack (£900) plus a sport automatic transmission (£1,690), split-folding rear seats (£170) and adaptive LED headlights (£1,200).

LED foglights, sports front seats and 18-inch light alloy wheels are thrown in at no extra cost.

Options aside, the new-look 4 Series is a step up from the previous model and when it comes down to all-round enjoyment it keeps its status as the best handling car in its class.