BMW Z4: BMW Z4 spy images

The big news is that the Z4's getting a folding metal roof for the first time. Look closely at these prototypes, and you’ll see that instead of a fabric affair, the new Z4 is following in the footsteps of its 3-Series Convertible big brother, plus its Mercedes SLK rival, with a retractable steel top.

As these pictures of a lightly disguised prototype show, the car will also get a more muscular look. And the convertible has another trick up its sleeve. BMW isn’t content with raining on the SLK’s parade, as it will seek to outgun the Porsche Boxster with a new range of powerful engines for the car. These are likely to include the twin-turbocharged 3.0-litre straight six-cylinder unit.

There’s even the possibility that the Z4 will be available with diesel power for the first time, too. And a flagship M model could get the new 4.0-litre V8 from the M3 – although a broad line-up of four-cylinder and normally aspirated six-cylinder petrol powerplants will continue to be offered. All cars will benefit from BMW’s Efficient Dynamics programme, which helps to cut CO2 emissions and boost fuel economy with features such as an engine stop/start facility.

Under the skin, the platform is shared with the latest-generation 3-Series, so the rear-wheel-drive Z4 will continue to provide pleasing handling for the purists.