BMW Concept 4-series Coupe (2012) first photos

BMW is overhauling the 3-series Coupe - it'll be replaced in 2013 by the new 4-series Coupe and Convertible, previewed in this remarkably production-ready concept car.

Munich reserves the 'Concept' moniker for its show cars which are in reality showroom ready. So strip away the sexed-up exhausts, 20in wheels and other trinkets and what you're looking at here is the new 2013 BMW 4-series.

This concept car will be shown at the 2013 Detroit auto show but CAR understands the production versions will be delivered to dealers by summer 2013.

Coupes come first, followed by the 4-series Convertible, which sticks with the folding hard-top solution, albeit further refined. And this time there'll be an extra bodystyle: a 4-series Gran Coupe.

Due in 2014, this is a four-door coupe in the mould of a baby Merc CLS. We've seen a similar treatment on the 6-series 4dr and BMW aims to repeat the trick with its smaller brother.

It marks an ambitious expansion for BMW of its heartland model: it's also planning a 3-series Gran Turismo, scooped totally undisguised by CAR earlier this week. It's not content resting on the laurels of its best-seller and is pushing the entire 3/4-series family into ever-more niches.

There are clues aplenty in this NAIAS show car. It's hardly a design revolution, instead preferring an elegant evolution of the existing 3-series aesthetic.

The 4-series sits low and squat, the front-end styling in particular emphasising the broadness of shoulder. BMW claims numerous 'Air Curtain' aero tricks keep airflow carefully managed for superior performance, economy and refinement.

No word yet on the engine in the BMW Concept 4-series Coupe, but it's safe to say the roadgoing two-doors will mirror the loftier echelons of the 3-series range, at launch at least.

That means a diet of four-cylinder petrol and diesel engines, mostly turbocharged and all tweaked by EfficientDynamics cleverness to trim emissions and fuel consumption.

BMW has been toying with the idea of upgrading two-door 3-series for at least a generation. It was rumoured to usher in the long-reserved 4-series badge at the launch of the E92 3-series coupe, but bottled it.

Now it's matching the strategy seen higher up the range, where a sensible 5-series saloon becomes a more sporting 6-series. Part of the reason is that they can sub-consciously charge higher prices for the higher digit. Word is the new BMW 4-series will cost around 2000 euros more than its equivalent 3-series.

By Tim Pollard