What is it?
Why did BMW wait for so long to launch a roadster version of the i8? A cynic may suggest that anyone who wanted an i8 had bought one already, and with some three-year lease deals of the early cars now coming to an end, now is a good time to tempt them into something else. Why would you want that 911, sir, when you can have an open-top version of one of these?
After all, a production-ready i8 roadster concept was seen in early 2016, when the i8 coupé was only a year or so into its life, and at that point selling on the used market for more than it was new.
In a world where frequent new variants are crucial to keeping up interest in your sports car no matter how radical yours looks – Porsche the master or stirring the mixing bowl another way every few months – BMW waited to launch this latest version of its sports car until demand had tailed off of the coupé.
At the same time as launching the roadster, BMW has taken the opportunity to upgrade the petrol-electric plug-in hybrid drivetrain of the coupé to the more potent offering of the roadster.
That upgraded drivetrain is focused on the electric side. The front wheels are driven through a 141bhp electric motor – an extra 12bhp from the earlier i8 coupé – and a two-speed automatic gearbox. The lithium ion battery is also larger – capacity rising from 7.1kWh to 11.6kWh – which gives the i8 roadster an electric-only range of 33 miles. It can travel up to 75mph on electric power, too, with charging times also cut thanks to an upgrading charging system.
The mid-mounted 1.5-litre three-cylinder turbocharged petrol engine, which drives the rear wheels through a six-speed automatic gearbox, carries over unchanged. The i8 roadster can therefore run on electric power as a front-wheel-drive car, or an all-wheel-drive car as a hybrid.
BMW says only 60kg has been added to the weight at the kerb of the i8 roadster over the coupé, an impressively low figure, and far less structural reinforcement is needed than normal thanks to the i8 roadster using an aluminium chassis with a high-strength, carbonfibre-reinforced polymer passenger cell.