How is the range of electric vehicles calculated?

This is undoubtedly the most important selling point of an electric vehicle. Battery range is crucial for a buyer to determine if the car can be suitable for their out-of-town trips. You don’t need to be a senior analyst to understand why a Chevrolet Bolt sells much better than a Mazda MX-30!

However, can we really trust the figures put forward by the manufacturers?

A government framework

In North America, the magic number is obtained according to the standards of the United States Environmental Protection Agency. I’Environmental Protection Agency (EPA). Although the EPA relies mainly on manufacturers to obtain consumption figures (of fuel or electricity), the American agency reviews all the tests submitted and will occasionally confirm the results (approximately 15 to 20% time) by performing the tests themselves at the National Vehicle and Fuel Emissions Laboratory in Ann Harbor, Michigan. And beware of manufacturers who would try to pass them a little quickly. For example, VinFast claims on its Canadian website that its VF 8 crossover can travel more than 471 kilometers, while according to the EPA, we would rather speak of 288 km in the combined cycle.

Testing methodology

The EPA rates the range of an electric vehicle by measuring its energy consumption on a chassis dynamometer, a large platform equipped with rollers on which the vehicle’s drive wheels will turn. The technicians subject the vehicle to two test cycles: the city test (Urban Dynamometer Driving Schedule) and the highway test (Highway Fuel Economy Driving Schedule). From a full charge, the vehicle will repeat the tests until the battery is drained for each of the two cycles. Then, the vehicle will be recharged to 100% on an alternating current terminal. The autonomy will then be calculated according to the energy used for the distance traveled during each of the two tests.

Below, we can look at the graphs of the two tests (images taken from the EPA website):

1. In the city test, we see that the vehicle does a lot of acceleration and braking over a distance of about 17.8 km. During the 31 minutes that the test lasts, the average speed is 34 km/h and we do not exceed 91 km/h.
   

   

2. In the motorway test, the vehicle maintains a higher (77 km/h) and more constant average speed: during the 16.5 km and 13-minute journey, the vehicle does not come to a standstill until the end. There are also peaks at 96 km / h.
   

   

Of course, we will agree that in a laboratory environment, the results are optimal. This is why the EPA proposes, among other things, two adjustment factors:

1. multiplication of range figures by 0.7;
2. performing three additional tests (high speed test, air conditioning test and cold weather heating test).

Finally, in order to have the value of combined autonomy, we will average according to a proportion of 55% in the city and 45% on the highway.

Are the results perfect?

Although EPA test cycles are more realistic than their European (WLTP, Worldwide Harmonized Light-Duty Vehicles Test Procedure) and Chinese (CLTC, China Light Duty Vehicle Test Cycle) equivalents, range may vary, not only due to the external environment, but especially to what is 18 inches behind the wheel… you!

For example, highway cruising speed will greatly influence the available range of the EV on the highway. Our American colleagues at Car & Driver have tested several electric vehicles at a cruising speed of 75 mph (120 km/h): of the 33, only 3 managed to exceed the autonomy expected by the EPA. That said, this deterioration is observed even on gasoline vehicles: between 100 and 120 km/h, an estimated 20% additional energy consumption. So, on a long trip, it is even more strategic to observe the speed limit.

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