2014 BMW i3 with Range Extender

Limited-Range Range Extender

The i3 is rated to cover 72 miles on electricity alone (or 81 miles without the weighty range extender), although as with every one of its peers, you can watch the predicted range drop five miles for every three or four you drive. BMW’s range-anxiety Prozac is a 647-cc two-cylinder engine turning a 34-hp generator. The gas engine, borrowed from BMW Motorrad’s C600 Sport scooter, never drives the wheels, making the i3 the only true series hybrid on sale today (R.I.P. Fisker Karma). Yes, we know, the Chevrolet Volt and the Cadillac ELR operate primarily as series hybrids, but GM allows their engines to drive the wheels directly in rare circumstances. BMW never does.

The range extender maintains a small buffer zone in the battery to reconcile the disparity between turning the wheels with a 170-hp electric motor and recharging the battery with a 34-hp generator. It takes an extra 0.9 second to get to 60 mph with the gas engine turning, and it’s possible to outpace the generator with sustained accelerator application. A driver spiriting the i3 around our real-world testing loop saw the car struggle to maintain 65 mph while climbing one of the slight grades that pass for hills in Michigan. That’s an extreme example, though. On the highway, the i3 buzzed happily at 80 mph, the engine humming audibly but not intrusively.

The single significant flaw with the i3’s range extender is that it drinks from a Big Gulp–sized gas tank. At 1.9 gallons small, the gas reservoir contributes another 75 miles or so to the i3’s reach, but the range indicator drops at an alarming rate, no better than when the car is running on battery alone. So it alleviates the anxiety of driving an electric but doesn’t solve the range issue the same way a Volt does. Take the i3 on a 500-mile weekend and you’ll stop to refuel every hour. Wasn’t driving an electric car supposed to be about avoiding gas stations?

The i3’s stunted range is a product of policy, not product planning or technical capability. California’s zero-emission-vehicle mandate allows BMW to earn credits for range-extended i3s as if they were pure battery-electric cars rather than hybrids—but only so long as the electric range meets or exceeds the gas range. The i3 would be far more practical and the $3850 premium for the range extender would be much more palatable if the gas tank simply held another five gallons of fuel.

The EPA rates the range-extended i3 at a combined 117 MPGe when running on electricity and 39 mpg when the gas generator kicks on. We recorded an average of 60 MPGe when totaling our fuel and electricity consumption. Admittedly, we burned as much gas in a week as many i3 owners will use in a month or three because we left the i3 unplugged several times just to experience the car with the range extender running.