To provide roll-over protection and boost chassis stiffness, there are prominent safety hoops, faired-in by body panels, at the rear of the cabin.
Although this concept leaves the design of the roof unclear, BMW insiders suggest that a removable panel, probably fashioned from carbonfibre, is the favoured solution.
The rear end has also been modified, with a flat, transparent engine cover in place of the sloping coupé roofline. It doubles as the luggage cover, over a wide but shallow stowage space.
As with all future BMW ‘i’ sub-brand models, the Spyder is based around a lightweight carbonfibre-reinforced plastic structure clothed in body panels of the same material. It is 4480mm long, 1922mm wide and 1208mm tall. That makes it 130mm shorter, 142mm wider and 187mm lower than a 335i cabriolet.
The snug 2+2 layout of the i8 coupé has been ditched for a pure two-seat cabin, with the rear bulkhead moved forward to provide added space for the engine. With a 2650mm wheelbase, accommodation is described as “generous”.
The i8 Spyder has the same plug-in petrol-electric hybrid system used by the i8 coupé. The 1.5-litre three-cylinder turbo petrol engine is mid/rear-mounted and delivers up to 220bhp to the rear wheels. The same engine will be offered in future Minis and a new front-wheel-drive entry-level BMW.
In the i8 Spyder, the 1.5-litre petrol engine is mated to a front-mounted 129bhp electric motor driving the front wheels via a fixed-ratio gearbox.
The i8 powertrain can operate on petrol or electric power, or a combination of the two and in either front, rear or four-wheel drive. A range-extender function recharges the battery on the move.
Gallery: BMW i8 Spyder concept
Together the petrol and electric motors make 349bhp and 405lb ft of torque.Computer simulationssuggest the 1630kg i8 Spyder’s 0-62mph will be 5.0sec, with 50-75mph in 4.0sec. Top speed limited at 155mph.
BMW is holding firm to claims that a combined 94mpg is possible, together with an all-electric range of up to 19 miles.
With the lithium ion battery sited within the centre tunnel and the petrol tank behind the rear bulkhead, BMW is claiming 50:50 weight distribution.
Technical details of the battery remain secret, although BMW reports a 1hr 45min recharge using a high-voltage supply. A recuperation system is also included to collect kinetic energy produced under braking and on a trailing throttle.
Pricing is likely to be in the region of £80,000.