The long-awaited BMW i8 Roadster has gone on sale, the first open-topper from the German manufacturer’s hybrid electric sub-brand.
First shown as a concept at the Beijing Auto Show back in 2012, the two-seater will sit in showrooms alongside the existing i8 2+2 coupe.
Like the coupe model, the new i8 Roadster is powered by a combination of a British-built petrol engine powering the rear wheels and an electric motor driving the front wheels.
According to BMW, much of the concept has been retained in the production version, particularly the signature dihedral doors and clever packaging of the roof. This opens or closes electrically in 15 seconds, at speeds of up to 31mph – the fastest operating roof in the BMW range.
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Folding roof
When opened, the three segments of the roof fold back vertically in a Z shape, which frees up 100 litres of storage capacity between the roof box and the seats. The rear compartment of the car accommodates another 68 litres. When the roof opens the rear screen raises 3cm to cut turbulence, and its height can be adjusted by the driver.
The i8 Roadster’s structure combines aluminium with CFRP (carbon-fibre reinforced polymer) and includes 3D printed parts connecting the roof to the body. This process allowed the components to be produced in a geometric form not possible with traditional casting techniques.
A combination of a three-cylinder turbo petrol engine and an electric motor provides the hybrid powertrain, the engine driving the rear wheels through a six-speed automatic transmission, and the electrics driving the fronts using a two-speed auto gearbox. Since its launch in the original i8 coupe the hybrid technology has been developed, and the electric side now solely provides the propulsion much more frequently, the engine only used for hard acceleration.
The capacity of the lithium-ion battery has been increased from 20 to 34Ah, allowing an increase in electric power by 12hp to 143hp and the ability to travel 33 miles in electric-only mode. The car can reach 65mph from rest on electric power alone, or 75mph if an ‘eDrive’ boost button is pressed.
The 1.5-litre petrol engine now puts out 231hp and 320Nm of torque. combined system power is now 374hp, which means the i8 Roadster will reach 62mph from rest in 4.6 seconds and go on to an electronically limited 155mph. And it will do this while returning combed cycle fuel economy 141.2mpg and CO2 emissions of 46g/km.
However, such technology comes at a cost. Prices for the i8 Roadster start from £124,735.
