An interview with BMW engineer Ulli Kranz conducted by Consumer Reports suggests that the BMW i3 city car will get a range extender similar to the i8 supercar but the technology will come from two-wheeled transportation, rather than a conventional car.
With weight a key consideration for the i3 (materials like aluminum and carbon fiber play a key role in offsetting the weight of the electric drivetrain), one of BMW's motorcycle engines seems like a much better fit than one of their current passenger car mills, the smallest of which is a 1.6L four-cylinder from the MINI range.
BMW's bikes, on the other hand, have a range of engines ranging from a 652-cc, 48 horsepower single cylinder to a 1.6L inline-6 maiking 160 horsepower. If anything, the single cylinder, or the 800cc twin are the most likely candidates.
More: BMW i3 May Get Range Extender Based On Motorcycle Engine