If you're a fan of electric cars, there's a fair chance BMW's i3 urban electric car is one of the vehicles you're most looking forward to in 2013.

When it goes on sale in the fourth quarter of 2013, it's set to be one of the most advanced vehicles on the road--not least for its lightweight carbon-fiber reinforced plastic chassis.

BMW is also releasing further details on the range-extended option for the i3, allowing drivers just that little extra range for longer trips.

The company hinted a while back that the gasoline-aided version of the i3 would use a twin-cylinder motorcycle engine.

The tiny unit, expected to be an inline-twin of around 600cc, will have no mechanical connection to the wheels, and will be used to turn a generator, extending the car's range once the battery has reached a lower limit.

Automotive News reports the car's range is expected to be around 250 miles, including the 60-90 miles possible on the car's battery pack. It'll lie under the rear deck, in the same compartment as the car's electric drive motor.

If 250 miles doesn't sound like a lot, then that's still more than most owners are likely to need, according to BMW.

"I imagine many buyers will order the range extender to cure their range anxiety, discovering later they need it very seldom," said BMW R&D cheif Herbert Diess.

Drivers of the Chevrolet Volt, another range-extended electric vehicle, will no doubt agree--63 percent of miles traveled by Volt drivers are on electric power alone--despite an all-electric range around the 40-mile mark.

The BMW's range-extender is unlikely to be a straight carry-over from one of the company's motorcycles, however.

Due to strict targets for noise, vibration and harshness, it's likely that BMW will heavily modify the engine for its intended purpose, and optimize it for the constant speeds needed for optimum efficiency.

BMW hasn't yet revealed pricing for the i3 or range-extended i3, but both will appear on sale together at the end of 2013.


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