Looks and brains make BMW's new i8 Spyder an alluring proposition

Convertible hybrid edition to debut at this year's Beijing Motor Show.

The i8 will be available as both a coupé and convertible. Newspress

The sultry next step in the longest-running car launch in history continues with BMW revealing a convertible version of its 2014 i8 hybrid sports car.

While BMW wheeled out the precursor to the i8 Coupé as far back as the 2009 Frankfurt Motor Show, its new i8 Spyder is far more true to its production future.

Its see-through glass doors have gone, replaced with a more conventional-looking pair, albeit doors that swivel up to open and have no window glass.

Due to make its debut at this month's Beijing Motor Show, the i8 Spyder will be at the more alluring end of BMW's new i brand of fuel-efficient green cars, with the smaller, all-electric i3 hatchback giving a clear indication of where BMW sees the entry point for the new line-up.

BMW had always hinted that the i brand would have more to it than just the two models, and the Spyder provides the first genuine clues to how the brand's coolest car will work in production.

Both the convertible and coupé versions of the tech-rich sports car will be built around a plastic tub, reinforced with short-strand carbon-fibre, and the bodyshell is said to be made from the same ultra-strong, lightweight structure. It means that the i8 Spyder will tip the scales at 1,630kg - considerably lighter than the similarly sized 6 Series.

It shares much of the coupé's distinctive silhouette, though its windscreen stands proud of the bodywork thanks to reinforced A-pillars, while it has fixed rollover hoops that incorporate their own bodywork, but a lot of the Formula One-esque aero kickers and vanes are gone.

BMW has yet to indicate whether the production versions of the i8 Spyder would carry a cloth or a targa roof, though the smart money is on a clear glass lid. Speaking of which, it also runs a clear cover above the petrol engine, through which can be seen its two portable electronic kickboards, which BMW says are perfect for moving around city footpaths.

The company insists the convertible version of the fuel-sipping hybrid will still hit 100kph in five seconds, and its heart and soul remains the same combination of a three-cylinder, turbocharged petrol engine for the rear wheels and an electric motor mounted up front to power the front wheels.

Planned from its earliest briefings to be a plug-in hybrid, the i8 Spyder's direct-injection, variable-valve timed petrol engine will pump out 220hp - not bad from three 0.5L cylinders. At its heart, it's the same triple motor that is being planned for both the Mini and BMW's forthcoming front-drive range, and its all-aluminium architecture means it can be built on the same production line as BMW's more-conventional four- and six-cylinder engines.

The petrol motor is backed up by a 128hp electric motor and the i8's powertrain combines for a total of 348hp and 550Nm of torque. The partnership of the two powerplants has BMW insisting the i8 Spyder will have a combined city/highway fuel economy figure of just 3.0L/100km.

The i8 Coupé and Spyder are scheduled for production, based at the Leipzig plant in northern Germany, and should be in dealerships around the world from late 2014.