What's the news?
So here we are then, after being teased with it for what feels like aeons, BMW has finally given us the full reveal and details on the i8 Roadster, the open-top version of its magnificent hybrid sports car.
The two-seat i8 Roadster received its world premiere at the Los Angeles Auto Show and will hit world markets from May 2018, alongside an updated version of the i8 Coupe from which it has spawned. Using the i8's carbon-fibre tub means there's little that needs to be done to strengthen the Roadster, although BMW does talk of model-specific structural elements to brace the open-top i8. The roof is made of fabric and can be lowered or raised in just 15 seconds, even while on the move at speeds of up to 50km/h, while a windscreen frame made from carbon fibre-reinforced plastics (CFRP) help to keep the weight penalty over an i8 Coupe to a reasonable 60kg.
Like the existing i8, the Roadster can travel at up to 120km/h in silent eDrive mode and it comes on a set of 20-inch double-spoke design light alloy wheels, that are each around a kilo trimmer than the previously lightest alloys available for the i8. Cleverly, that soft-top stows away in a vertical position, which frees up an additional 92 litres of storage space behind the seats when it's folded down. BMW says it has given the soft-top i8 its own specific tune for the springs, dampers and Dynamic Stability Control, as well.
New colours are offered for both the Roadster and the Coupe, which are E-Copper metallic and Donington Grey metallic, while there are additional interior finishes too. The tile-design BMW Navigation Professional is drafted in, as are the BMW Display Key, Driving Assistant including Surround View and a mode 2 charging cable. Options will include Head-Up Display, BMW Laserlight with BMW Selective Beam and acoustic pedestrian warning. About the only external visual difference between the Coupe and Roadster i8s is model-specific badging on the rear and on the C-pillar.
Anything else?
So, let's talk about the drivetrain. It's the familiar i8 set-up, featuring a mid-mounted 1.5-litre turbocharged three-cylinder petrol that drives the rear wheels, while an e-motor controls the fronts. The combustion engine remains unchanged at 231hp but the e-motor and the lithium-ion battery pack have both been uprated, to 105kW/143hp (+9kW/12hp) and 11.6kWh/34Ah (previously 7.1kWh/20Ah) respectively.
That leads to quite a few benefits. Both i8s can go further on their electric power alone than the 'old' car, which did 38km of zero emissions motoring on a single charge. Now, the Roadster can go 53km and the Coupe, which is a bit lighter, 55km. They're therefore officially a tiny bit cleaner too, matching or beating the previous numbers of 134.5mpg (2.1 litres/100km) and 49g/km. The Roadster does the same economy but emits only 46g/km, while the Coupe is capable of 148.7mpg (1.9 litres/100km) and just 42g/km CO2.
Thanks to that extra 12hp in the e-motor, the total system output is also increased to 374hp, with the same 570Nm of peak torque cited. The 0-100km/h acceleration of the Coupe doesn't improve, however, still standing at the impressive 4.4 seconds, while the heavier Roadster is two-tenths slower. Both i8 models are limited to the 250km/h maximum.