How is the range of electric cars calculated?
This is undoubtedly the most important selling point of an electric car. Battery range is very important for the buyer to determine whether the car is suitable for out-of-town trips. You don’t need to be a big analyst to understand why the Chevrolet Bolt is selling better than the Mazda MX-30!
However, can the figures put forward by the manufacturers really be trusted?
In North America, the magic number is obtained according to the standards of the US Environmental Protection Agency. I’Environmental Protection Agency (EPA). Although the EPA relies mainly on manufacturers to obtain consumption figures (fuel or electricity), the American agency reviews all submitted tests and sometimes confirms the results (about 15-20%) by performing tests on the National Car and National Car. Fuel Emissions Laboratory in Ann Harbor, Michigan. Beware of manufacturers who try to pass them a little too 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 prefer to talk about 288 km on the combined cycle.
The EPA estimates an electric vehicle’s range by measuring energy consumption on a chassis dynamometer, a large platform equipped with wheels on which the vehicle’s wheels will spin. Technicians subject the vehicle to two test cycles: the city test (Urban Dynamometer Driving Schedule) and the highway test (Highway Fuel Economy Driving Schedule). Once fully charged, the vehicle will repeat the tests until the battery is discharged for each of the two cycles. The vehicle will then be charged to 100% at the AC terminal. The autonomy will then be calculated based on the energy used for the distance traveled during each of the two tests.
Below we can see the graphs of the two tests (images taken from the EPA website):
- In the city test, we see the car doing a lot of acceleration and braking over a distance of about 17.8 km. The average speed during the 31 minutes of the test is 34 km/h and we do not exceed 91 km/h.
- In the highway test, the car maintains a higher (77 km/h) and more stable average speed: during a journey of 16.5 km and 13 minutes, the car does not stop until the end. It also has peaks of 96 km/h.
Of course, we will agree that the results are optimal in a laboratory environment. Therefore, EPA is proposing, among other things, two correction factors:
- multiplying range numbers by 0.7;
- performing three additional tests (high speed test, air conditioning test and cold air heating test).
Finally, we will average 55% in the city and 45% on the highway to have a combined autonomy value.
Are the results perfect?
Although the EPA test cycles are more realistic than the European (WLTP, Worldwide Harmonized Light Duty Vehicle Test Procedure) and Chinese (CLTC, China Light Duty Vehicle Test Cycle) equivalents, the range can vary, especially not only according to the external environment. What 18 inches behind the wheel … you!
For example, highway cruising speed will greatly affect an EV’s available range on the highway. Our American colleagues at Car & Driver tested several electric cars at 75 mph (120 km/h): only 3 out of 33 cars managed to exceed the autonomy expected by the EPA. However, this degradation can be seen even in petrol cars: between 100 and 120 km/h, about 20% extra energy consumption. So it’s more strategic to stick to the speed limit on a long trip.