The Engineer Car Review: BMW i8

It's hard to believe that the BMW i8 has been with us for five years now. The basic design has remained largely unchanged since it debuted at the Frankfurt Motor Show in 2013. And yet it still looks like something that has teleported in from the future, complete with its concept car looks and those wonderfully flamboyant butterfly doors.

It’s not just a styling exercise, either. Underneath the lightweight (plastic and aluminium) panels, there’s a carbon fibre monocoque, which is mass-produced using a resin transfer moulding (RTM) process. The result is an immensely rigid structure that’s half the weight of steel and 30 per cent lighter than aluminium.

Power comes from a heavily turbocharged, three-cylinder petrol engine combined with a 105kW hybrid-synchronous electric motor. The internal combustion half of that package is based on the engine used in the MINI Cooper and the BMW 2 Series Active Tourer. Built at the Hams Hall engine plant near Birmingham, it squeezes 231bhp from just 1.5 litres. This is fed to the rear wheels via a conventional six-speed automatic gearbox, but that’s only half the story. On the front end there’s a self-contained ‘eAxle’ produced by GKN, which combines the electric motor with a differential and a two-speed synchro-shift transmission. This extends the motor’s speed and load range, allowing it to work right up to the i8’s electronically-limited top speed of 155mph. Combined, the two halves of the powertrain produce 374bhp; enough to propel the 1,535kg i8 from 0 to 62mph in 4.4 seconds.