The folks over at GreenCarReports have put together a comprehensive comparison test between the Tesla Model S and the BMW i3. The ultimate goal of this test is to compare the efficiency of the two most impressive electric vehicles on the market at the moment.
BMW i3 is rated at 125 MPGe while the 85 kW Tesla has a rating of 89 MPGe.
To level the play field, they used the same driving conditions for both cars: a 54 mile route, traveling at the same speed and in the same temperature. Inside, the AC was set at 70 degrees.
Here is an excerpt from their review:
The two cars read out their efficiency in different ways.
The i3 measures miles per kilowatt-hour (more is better), while the Tesla indicates watt-hours per mile (less is better). So it took few clicks on a calculator to convert the units.
At the end of the 54 miles, the i3 was showing that it had used 3.6 miles/kWh, while the Tesla displayed a reading of 322 Wh/mile.
Converting the units, the Tesla traveled 3.1 miles on a kWh (vs. 3.6 for the i3 REx), while the i3 used 277 Wh/mi of energy (vs 322 for the Tesla).
Bottom line: The i3 was only 16 percent more efficient than the Tesla–not the 31 percent the EPA says.