The unchanged 170kW/320Nm 1.5-litre turbocharged three-cylinder petrol engine drives the rear wheels. The 2019 BMW i8 Roadster and coupe both go on sale next spring. Located in the car's underbody, underneath the passenger cabin, the battery provides the i8 with a low center of gravity.
The biggest upgrade to the powertrain is a new 11.6 kWh battery pack up from the 7 kWh battery pack of the original BMW i8 and a slightly more powerful motor (12 more hp). Neither is the acceleration, though the 0-60 miles per hour times now stand at 4.2 seconds for the Coupe and 4.4 seconds for the roadster; 155 miles per hour remains the limited top speed. Top speed of both cars is electronically limited to 155 miles per hour. The combined power output of 369bhp and 570Nm is channelled through a six-speed automatic gearbox to the rear wheels.
BMW has added non-dazzling laser headlights to the i8's specification that boast an impressive high-beam range of 600 metres - double that of the current car's.
Its impact on the Frankfurt motor show was considerable - it's not every day you see a sports coupe hiding a plug-in hybrid system under its bodywork.
2018 BMW i8 Roadster adds open-top thrills to Munich's plug-in sports car
The roof can be opened and closed at speeds up to 50kph in 15 seconds, and its aluminium framework has been produced using 3D printing. When retracted, the soft-top folds into a compact package and stows away in a perpendicular position, creating around 100 liters of storage space behind the seats.
Pricing has not been announced, but a BMW representative told us the i8 Roadster will start "north of $150,000". This allows for geometric parts that can not be cast for the optimum strength and size to be used, balancing weight with rigidity requirements.
The dashboard is lightly updated for the i8 Roadster and i8 Coupe, with the latest version of BMW's iDrive system now offering either touch control on a free-standing 8.8-in. A Tera World Copper interior trim featuring premium cloth and leather upholstery in an Amido/E-Copper color scheme is new and exclusive to the Roadster.
The i8 Roadster will have exclusive 20-inch BMW i light-alloy wheels in radial-spoke style, lowering wheel weight by about 2.2 pounds versus the other wheels offered on the i8. Also aiding rigidity on the Roadster are additional panels in the suspension and special front and rear struts.