What's all this about?

We've been teased and tormented with the BMW i8 Roadster for what feels like a very long time now, but finally here is the full rundown. This new open-top version of the hybrid sports car will go on sale in May 2018, alongside a mildly updated i8 Coupe, and the Roadster was revealed to the world at the 2017 Los Angeles Auto Show.

Can you start on the technical side, please?

OK. Both the all-new Roadster and the revised Coupe use a slightly improved version of the i8's clever plug-in hybrid drivetrain. The 231hp, mid-mounted, 1.5-litre three-cylinder engine remains, where it drives the rear wheels, while up front there's the e-motor to bless the i8 with all-wheel drive. However, both it and the lithium-ion battery pack have been upgraded. There's an additional 9kW/12hp for the e-motor, while the storage density of the battery has increased from 20- to 34Ah, giving rise to a greater capacity of 11.6kWh compared to 7.1kWh before. This gives the i8s more peak power (374hp, as opposed to 362hp previously), leading to better eco-stats.

Will you outline those, please?

Both cars will now go for longer on electric power alone, at speeds of up to 75mph; the Roadster for 33 miles and the Coupe for 34 miles - you'd have got 23 miles prior to this, and that was your lot. The Roadster only matches the old i8's claimed 134.5mpg economy figure, but the Coupe can now purportedly achieve 148.7mpg, while both are cleaner than 49g/km for CO₂ - 46g/km for the Roadster, 42g/km for the Coupe. Performance doesn't improve, though, as the Coupe still does 0-62mph in 4.4 seconds (4.6 seconds Roadster), with both models topping out at an electronically limited 155mph.

Looking at these numbers, then, is the i8 Roadster heavier than the i8 Coupe?

Yes, but only by 60kg, which isn't too bad at all. There is some model-specific strengthening required as a result of the car losing its fixed roof, but the Roadster majors on the i8's carbon fibre-reinforced plastic (CFRP) construction to ensure it's rigid and not too hefty as a result. The roof is fabric and can be raised or lowered in 15 seconds at speeds of up to 30mph as well and once it's stowed away behind the Roadster's two seats, it sits vertically - liberating another 92 litres of storage space in the cabin in the process.

BMW says it has given the soft-top i8 its own specific tune for the springs, dampers and Dynamic Stability Control, while some new exterior colours, interior finishes and technologies (tile-design BMW Navigation Professional, BMW Display Key, Driving Assistant including Surround View and a mode 2 charging cable being just some of them) are all drafted in. There's also model-specific 'Roadster' or 'Coupe' badging on the rear and the C-pillars of these new i8s.