The BMW i8 Roadster has made its world premiere at the 2017 Los Angeles Auto Show. The topless sister to the fixed-top i8, now called i8 Coupe, features gullwing doors and a soft-top. The electric fabric roof with additional soundproofing does its thing in 15 seconds and up to 50 km/h.

BMW says that the i8’s carbon-fibre-reinforced plastic (CFRP) passenger cell’s robust structure means the soft-top could be designed with generous width for a big window to the sky. The soft-top stows away into a perpendicular position in the rear when opened and therefore takes up very little space. The three segments of the roof fold vertically in a Z.

Between the roof box and the two seats (i8 Coupe is 2+2) is around 100 litres of additional storage space. Together with the 88 litre rear load area in the rear, the i8 Roadster is not completely impractical. The 1,595 kg Roadster’s weight penalty over the Coupe is only 60 kg, thanks to newly-designed frameless gullwing doors made from CFRP with an aluminium outer shell, and a windscreen frame made entirely from CFRP, among other measures.

Opening the roof raises the rear window automatically by around 30 mm into a “comfort position”. This allows it to mimic the effect of a conventional draught stop in reducing air turbulence inside the cabin. The driver can adjust the height of the rear window at the touch of a button and thus control the impact of the inflowing air as desired.

The C-pillars of the i8 Roadster have the “Roadster” inscription. A similar logo can be found on the tail of the two-seater. The coupe gets its own “Coupe” badging at the same places.

Other styling cues are shared. Highlights include gullwing doors, the low bonnet, almost fully blanked off kidney grille, air flap control system, Air Curtains in the front apron, sealed underbody, contoured side skirts, “stream flow” lines on the flanks, and air ducts between the rear lights and roof frame.

The flow of cooling air at the front has now been rerouted. Instead of rushing out through the outlet in the bonnet, the air escapes at the sides of the car near the wheel arches and into the underbody. This ensures that a pleasant cabin temperature is maintained at all times, especially when travelling in the i8 Roadster with the roof down.

E-Copper metallic and Donington Grey metallic have been added to the choice of exterior colours for the i8 range. Both are combined with accents in Frozen Grey metallic. The i8 Roadster rolls on 20-inch alloys in an exclusive double-spoke design. Each wheel weighs around one kg less than the lightest rims previously available for the i8.

The i8’s eDrive powertrain has been optimised. The number of driving situations where the electric motor is solely responsible for powering the car has been significantly increased. By contrast, the combustion engine is only brought into play when accelerating hard, and is switched off again far more frequently with a measured driving style, BMW says.

Underpinning this is an updated version of the lithium-ion battery. Located centrally in the car’s underbody, the battery’s gross energy capacity is up from 7.1 to 11.6 kWh (net energy capacity 9.4 kWh). Plus, the cell configuration allows a 12 hp increase in peak output to 143 hp (torque remains at 250 Nm from rest).

The better battery means that all-electric range is up, and the i8 Roadster can do 53 km with zero local emissions in the NEDC test cycle (55 km for the Coupe, around 50% more than before). Pressing the eDrive button enables pure electric driving up to 120 km/h; otherwise it’s 105 km/h max.

The BMW TwinPower Turbo 1.5 litre three-cylinder engine’s unchanged 231 hp/320 Nm output is channelled to the rear wheels through a six-speed automatic transmission, while the electric motor propels the front wheels via a two-speed automatic gearbox. The combustion engine’s acoustics (sportier note) and emissions have been optimised, the latter with an integrated particulate filter. Combined fuel consumption for the i8 Roadster is 2.1 litres per 100 km, or 1.9 litres per 100 km for the lighter Coupe.

Combined system output is now 374 hp, and 0-100 km/h takes 4.4 seconds in the Coupe and 4.6 seconds in the Roadster. The topless i8 has model-specific tuning for the springs, damping and Dynamic Stability Control. Both models come as standard with Dynamic Damper Control.

Standard kit includes Navigation system Professional, BMW Display Key and Driving Assistant including Surround View. Options include BMW Head Up Display with model-specific content, non-dazzling BMW Laserlight with BMW Selective Beam, and acoustic pedestrian warning. ConnectedDrive Services come as standard.

Both models are supplied with a mode 2 charging cable as standard, enabling the battery to be replenished from a standard domestic socket in under four-and-a-half hours. The new mode 3 cable can also be used to hook up the car to a public charging point for high-power charging. The latest BMW i Wallbox allows the battery to be recharged at a rate of up to 3.6 kW, meaning that a full charge can be completed in under three hours. The i8 Roadster’s market launch will happen in May 2018.

GALLERY: 2018 BMW i8 Roadster and Coupe