BMW i8 prototype first drive

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.

The three-cylinder petrol engine does sound a bit gruff when it kicks into action. But once you’ve got it percolating above 4000rpm, the i8 emits a satisfying deep-chested thrum that becomes more sporting the closer you venture towards the 7000rpm cut out. The appealing acoustics aren’t all from the engine itself, though. As with the latest iteration of the M5, BMW has combined the actual sound of the engine with a synthetic sound generator to arrive at the desired result. They call it progress...

With the front electric motor and petrol engine providing drive to the front and rear wheels respectively, there is genuinely impressive acceleration in Sport mode, in which there is a noticeable change in character, with added throttle and steering response along with firmer damping for greater body control. The official acceleration claims – 0-62mph in 4.5sec and 50-75mph in 4.5sec – put the i8 on par with the outgoing BMW M3 for outright straightline pace. No slouch, then.

I drove the i8 on BMW’s Miramas test track in France. On the infield handling course and surrounding roads, it immediately dispelled any lingering doubts about its ability to deliver truly engaging driving traits. It is extremely agile, with somewhat light but extremely direct electro-mechanical steering. You can sense the low centre of gravity in the way the futuristic looking coupé enthusiastically turns in to corners. Its dynamic properties are characterised by an inherent responsiveness, nimbleness and light-footedness to the handling, which immediately stands out as one of the new car’s strengths.

There is very little body movement as lateral forces rise, although its ability to carry serious speed through corners is limited by the current state of chassis tune, which clearly favours understeer – something it tended to do quite early on the freshly laid bitumen of the BMW test track. It’s nothing too troubling, mind. But when the rest of the car is so well sorted, the deficiency in front-end bite tends to be magnified, and it quickly had the DSC (dynamic stability control) working as we began to push the i8 hard through corners.

BMW’s engineering team says the understeer is partly down to the characteristics of the specially developed Bridgestone Potenza tyres. They boast relatively soft side walls and are engineered to deliver low rolling resistance for maximum efficiency, even with the optional rubber. Still, this is an engineering mule, not a pre-production prototype, and predictably BMW says there are developments in the pipeline that will provide the definitive production version of the i8 with greater mid-corner purchase than the example we sampled.