The roof, which opens and closes electrically in 16 seconds at speeds up to 31mph, folds up into a Z shape which BMW says frees up 100 litres of storage room over the coupe, as well as still offering an 88-litre rear luggage compartment.
The i8 has always had a lot going on in the styling department – with its visible aerodynamics, flat bonnet, dihedral doors and signature two-tone plastic body panels. The Roadster’s achievement is to look just as dramatic as the coupe while retaining a very cohesive look, despite what is substantial remodelling of the rear body.
In place of the coupe’s glassed-in rear section are twin buttresses flanking a vertical glass screen, which automatically rises up to reduce turbulence when the roof is open. It can be lowered if you want maximum fresh air. BMW says a lot of the aluminium elements connecting the roof with the body are produced in a 3D printing process that breaks new ground for the motor industry.
The Roadster, like the newly-updated coupe version, will go half as far again in emission-free electric mode as the previous i8. Beefed-up lithium-ion batteries – they have gone from 7.1 kWh to 11.6 kWh – now offer an electric-only range of up to 33 miles, with speeds up to 75mph possible. The electric motor driving the front wheels gets 12bhp more power (now 141bhp) while the 1.5-litre petrol triple driving the rear wheels is unchanged in power (at 228bhp) but is said to sound sportier than before.
The battery pack is charged up by recovering lost power on the overrun and during braking, and also by the petrol engine via the starter-generator unit. But as a plug-in hybrid it will also need plugging in from time to time. A full charge takes four and a half hours with standard cable or, with the iWallbox, under three hours, says BMW.
With a combined 369bhp, the new Roadster is credited with a 0-62mph time of 4.6 seconds, two-tenths behind the identically-updated coupe. The Roadster’s fuel consumption suffers more next to the coupe, but then it still records 134.5mpg on the combined cycle. For mixed driving the new beefier batteries of both Roadster and coupe should give a boost to real-world consumption (realistically, 40-50mpg) by ensuring the electric motor does more of the work, leaving the petrol unit idle more often.
In light of that one new option would seem sensible. It’s an acoustic pedestrian warning system that emits a “turbine-like” sound when the car is driving in electric mode at low speeds.
Heavier? Inevitably yes but with a lot of body parts – including new frameless doors, windscreen surround and side skirts – in carbon-fibre reinforced polymer (CFRP) like the body, the Roadster’s weight comes in at 1595kg, 60kg heavier than the coupe.
Both 2018 Roadster and coupe get a refreshed cabin and styling tweaks up front to reroute airflow, along with new non-dazzle laser headlights. There are new colours and new wheels too, along with new prices: £112,730 for the i8 coupe and £124,730 for the i8 Roadster. On sale January.