Like its smaller sibling, it can run in pure electric mode, but only for distances of up to 22 miles and a top speed of 75mph owing to its relatively small battery. Overall range promises to be quite spectacular thanks to a 42-litre fuel tank that is mounted underneath the rear seats. BMW is not prepared to make a figure official but it is already quite clear that the i8 will be among the most fuel efficient sportscars ever placed into production.
The i8’s styling has evolved during the four-year development phase, although the basic silhouette and flamboyant layered body design has been retained, giving the i8 a strikingly futuristic external appearance which is carried through to the snug two-plus-two interior. Length, width and height are put at 4689mm, 1942mm and 1293mm respectively, making it 449mm longer, 152mm wider and a scant 3mm taller than the second-generation BMW Z4 – a car against which the new BMW has been extensively benchmarked.
As with the i3, the i8 makes extensive use of carbonfibre and aluminium in a bid to offset the inherent weight of its advanced driveline. A so-called Life Module fashioned from carbonfibre forms the main structure, to which BMW has attached carbonfibre-framed doors and aluminum sub-frames both front and rear.
The outer body is a combination of carbonfibre (roof), aluminium (bonnet and outer door panels) and composite plastic (bumpers, fenders). BMW has also revealed the i8 will be the first production car to make use of Gorilla Glass – as seen on the latest smart phones. It is used for the rear window, providing added sound deadening properties for the interior.
A definitive figure is yet to be revealed, though the i8 is claimed to weigh less than 1490kg – undercutting the two seat Z4 sDrive35iS by 35kg despite providing accommodation for up to four adults (at a squeeze) along with 150 litres of luggage space underneath a liftback-style tailgate at the rear.
The primary form of propulsion for the i8 comes via a compact, turbocharged 1.5-litre three-cylinder petrol engine – the same B38 designated unit earmarked to head into a production version of the BMW Compact Active Tourer and third generation of the modern day Mini in 2014, albeit in a milder state of tune than the 2.0bar of turbocharger boost pressure used on the i8.
Mounted transversely behind the cabin, the aluminium block unit delivers an impressive 228bhp, giving it the highest specific output of any existing BMW engine at 152bhp/litre, along with 236lb ft of torque – all sent to the rear wheels via a six-speed automatic gearbox boasting a conventional torque converter.
The efforts of the compact petrol engine are supported by two electric motors, the larger of which is mounted up front within the front axle assembly, which is shared with that on the four-wheel drive BMW 650i xDrive. With 129bhp and 184lb ft of torque, the unit channels drive through a two-speed automatic gearbox.
The front electric motor is used to drive the front wheels during the start-up phase provided there is sufficient charge within the battery, a 5kWh lithium-ion unit that is housed within the centre tunnel, providing the i8 with zero local emission capability – something that will enable it to enter sidestep city charges like that in place in London. It also chimes in to boost performance in combination with the petrol engine, providing the i8 with four-wheel drive capability
There is also a smaller electric motor with 13bhp and 81lb ft sited at the rear next to the combustion engine. But while it is capable of providing additional drive to the rear wheels, it is principally used as a generator to top up the battery and alternatively as an alternator to collect and store kinetic energy during braking and periods of trailing throttle.
Interestingly, the rear electric motor is also used to smooth out delivery by providing direct drive to the rear wheels as the petrol engine is brought into the drive process. In doing so, BMW claims to have eliminated a slight dip in delivery due to typical turbocharger lag.
BMW quotes a combined 357bhp, endowing the carbonfibre intensive i8 with a power-to-weight ratio that betters that of the steel-bodied Z4 sDrive35i at 240bhp/tonne. Combined torque peaks at 420lb ft, some 44 per cent of which is available the moment you brush the throttle thanks to the inherent qualities of the electric motors.
As with the i3, the i8 receives three distinct driving modes: Comfort, Sport and Eco-Pro – all of which involve a combination of electric and petrol engine propulsion, albeit with different throttle, steering and damping mapping.
Underpinning BMW’s new age supercar is a largely aluminium chassis boasting double wishbones up front and a five link arrangement at the rear. The latter set-up is mounted directly to the aluminium sub-frame that supports the combustion engine and smaller of the electric motors. In keeping with BMW engineering philosophy, the new car boasts what the i8's project leader, Carsten Breitfeld, describes as a "near to perfect 50:50 weight distribution". The electro-mechanical steering system is borrowed from the X3, albeit with unique programming that aims to provide the i8 with sharper reactions.
The standard-fit wheels are aerodynamically optimised and measure 20 inches in diameter. They are 7.0 inches wide up front and 7.5 inches wide at the rear, shod with relatively narrow and high profile 195/50 and 215/45 tyres respectively. Buyers will be able to order more conventional 20in alloy wheels with wider 215/45 and 245/40 profile rubber – as fitted to the car i8 prototype we drove – for added grip.