BMW i3 REx Adding Two-cylinder Engine

Buyers of BMW's upcoming i3 city car will have a choice to make: pure electricity, or electricity with a dash of petrol-powered range extension. 

For now, BMW has revealed only one version of the little i hatch, which uses a 125kW/250Nm electric motor and lithium-ion battery pack to deliver a driving range of around 160km.

Another variant, known as the i3 REx, will add a version of BMW Motorrad's two-cylinder petrol engine to boost the hatch's range to around 400km.

Like the Holden Volt, the petrol engine will work to power a generator that will in turn charge the i3 REx's battery pack on the go, kicking in only when the pack's charge falls to a certain point. 

Speaking with industry paper Automotive News, BMW's Herbert Diess said that he expects the REx to prove a popular choice among buyers not yet ready to embrace the relatively short driving range of pure electric vehicles.

"I imagine many buyers will order the range extender to cure their range anxiety, discovering later they need it very seldom," he said.

"For those who plan a daily use of the range extender, probably the i3 is not the right choice, with a plug-in hybrid model being a better suitable solution."

He added however that most buyers drawn to a car as small as the i3 are unlikely to drive further than 160km on any given trip, suggesting the REx's petrol engine will rarely see action.

Revealed as a concept in 2011, alongside the supercar-styled i8 Coupe, the i3 is expected to make its production debut at September's Frankfurt Motor Show.

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