39 MPG combined isn’t going to win any hypermiling contests, but for the 2015 BMW i3 REX, it’s an acceptable trade-off for its unique purpose: emission-free city driving most of the time, and the reassurance of a gasoline safety net when needed. The i3 REX, with its range-extending gasoline engine, wasn’t conceived as a long-distance cruiser. It was designed for urban commutes and errands, targeting environmentally conscious buyers who experience occasional range anxiety when considering a full EV.

City and highway performance

The EPA estimates 41 MPG in the city and 37 MPG on the highway for the 2015 i3 REX. This reflects the nature of its powertrain. In pure electric mode, as long as the battery is charged, efficiency is solely determined by electricity consumption, a completely different metric. The gasoline engine only kicks in when the battery is depleted, acting as a generator to maintain a minimal state of charge. Therefore, the city MPG slightly edges out the highway figure because of the regenerative braking system. In urban environments, frequent decelerations capture kinetic energy, bolstering the electric range. On the highway, the gasoline engine is likelier to engage for sustained periods, leading to its lower MPG rating.

Annual fuel cost

The EPA estimates an annual fuel cost of $1,500 for the 2015 BMW i3 REX. This figure is calculated based on 15,000 miles of driving per year and the national average fuel price at the time of testing. This estimate assumes the vehicle is used frequently enough to activate the gas engine for sustained periods. Real-world fuel costs largely depend on charging habits. Given the i3’s limited gas tank, and relatively poor fuel economy when using that tank, regular charging is the only way to meet or beat the $1,500 annual estimate.

Real-world expectations

Owners considering the 2015 i3 REX aren’t primarily motivated by fuel savings; they are focused on minimizing their environmental impact and enjoying the unique driving experience of an electric vehicle. Many i3 REX owners report significantly lower fuel costs than the $1,500 EPA estimate, provided they primarily use the car for short trips and consistently charge the battery. Some owners drive weeks or even months between fill-ups. However, those who frequently rely on the range extender will experience lower MPG figures that align closely with the EPA’s estimates, and will incur higher annual costs.

How it compares

Compared to other plug-in hybrids of its time, the i3 REX’s MPG is both impressive and misleading. The Chevrolet Volt, for example, offered around 42 MPG combined when its gasoline engine was active. The Toyota Prius Plug-in achieved similar numbers, around 50 MPG in hybrid mode. However, both those vehicles were intended for prolonged hybrid use. The i3 REX, in contrast, was meant to be driven primarily on electricity, with the gasoline engine as a last resort. Looking at pure electric vehicles, the Nissan Leaf presented a vastly different offering, with its total reliance on charging and zero gasoline consumption. For those seeking to compare I3 MPG across all years, there’s plenty more to learn.

Tips to maximize efficiency

Prioritize charging the i3 whenever possible. This car is an EV first and foremost. Keeping the battery topped up reduces reliance on the range extender, essentially eliminating gasoline consumption for daily commutes. Use regenerative braking to your advantage. The i3’s strong regenerative braking system recovers energy during deceleration, extending the electric range. Learn to anticipate traffic and coast whenever possible, maximizing energy recapture.

Minimize highway driving. Where possible, use local roads. The range extender operates less efficiently at highway speeds compared to city driving, reducing the fuel-saving benefits of the electric powertrain. Plan longer trips carefully. Always check charging locations. On longer trips, plan routes that incorporate charging stations, allowing you to replenish the battery instead of relying solely on the range extender. Review all Bmw fuel economy data to understand how this stacks up for the brand overall.

Maintain proper tire inflation. Correct tire pressure reduces rolling resistance, improving both fuel efficiency (when the range extender is in use) and overall efficiency in electric mode. Check your tire pressures more frequently in colder months. Limit the use of energy-intensive features. Heavy use of air conditioning or heating drains the battery faster, forcing the range extender to engage sooner. Try to pre-condition the cabin while the car is plugged into a charging station to minimize this.

Consider eco-driving modes. Selecting “Eco Pro” mode adjusts throttle response and other vehicle settings to optimize energy consumption. It might not transform the i3 into a sports car, but it will noticeably extend your electric range.