Why We Test EVs the Way We Do

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Testing is a core principle in Car and Driver, something that has been incorporated into everything we do since 1956. This objective data base combined with our subjective observations brings serious depth to our review. This allows us to go from statements like “this car feels faster to 60 mph” to definitive conclusions about speed, cornering grip, interior noise, cargo volume, and a number of other important vehicle attributes. But the relatively recent influx of electric vehicles has caused us to tweak our usual testing regimen in a number of ways, and we’ve also added some EV-specific tests for range and charging.

Most Tests Still Same, Some Changed

Whether or not the car is powered only by electrons didn’t affect much of our testing, which included things like inserting a suitcase-sized box into the back of the cargo area, measuring how much the vehicle’s pillars block outward visibility, or seat height. And the fact that we weighed every car we tested allowed us to track exactly how much the EV weighs more than a comparable gasoline-powered vehicle.

We always fill the gas tank before weighing the vehicle. But that’s not necessary with an EV, as a fully charged battery is no longer a burden. For our performance tests—acceleration, braking, skidpad, top speed—we modified the test sequence for the EV. Because the maximum power output of the battery pack decreases as the charge state decreases, we always do our stand-start acceleration first with the battery as close to 100 percent as possible. We usually mount the test vehicle in the charger array on the test track and fully charge it, which leaves us about a mile to get to the live track. Another juice option we use from time to time is to fully load the vehicles in our office and then haul them to the test track in a trailer.

75-MPH . Highway Range Test

Range is a very important number for EV buyers, far more important than the vehicle efficiency (MPGe) number. Each vehicle has a coverage number displayed on its window sticker, which conforms to the EPA methodology. But we wanted to create our own real-world range numbers for two big reasons: first, there is some wiggle room in EPA rules, and automakers are allowed to use different methods to arrive at those range numbers. That means the EPA coverage figures don’t always give an exact comparison between the two vehicles. In addition, the EPA test cycle ran at a much slower speed than drivers typically experience on our interstate highways. We chose 75 mph for our test because driving at steady high speed is the worst case range for an EV (this doesn’t apply to gas-powered cars, which we ran at 75 mph to get highway fuel economy figures). Another reason is that range matters most in scenarios like road trips where you drive miles in a day; almost every EV on the market has enough range when stuck in slow city traffic for hours on end.

We run our range tests primarily on the highways around our Ann Arbor, Michigan, office, and we usually run them in the middle of the day, or at night or on weekends, when traffic is lightest. We started with a full load and ran at a GPS-verified 75 mph for as long as we could, turning around halfway to return to our office parking lot. We record the entire trip with a VBox LapTimer or Driftbox and also record battery charge status and estimated vehicle range every five miles. We compile those data points into two trendlines that we use to estimate the last few percent of the battery we don’t use. We were generally surprised at how linear the drop in battery charge was, and there wasn’t a major drop along the way to zero. We then round the range to the nearest 10 mile increment.

plug in electric car to charge

SimonSkafar|Getty Images

Some EVs got 20 percent less reach than the window sticker numbers in our road tests, though others, usually from German automakers, have already surpassed their EPA coverage figures. This validates our reasons for doing our own testing, both because highway coverage is well below the window sticker numbers and because the numbers aren’t a perfect apples-to-apples comparison.

DC Fast Charge Test

Another EV-specific test we conducted was the fast charge test, where we charged each vehicle from 10 to 90 percent charge state on the fastest charging equipment the vehicle could handle. Why not everything from blank to 100 percent? First, it’s logistically challenging, but it’s also not how EV owners use fast charging. Since the charging rate slows down significantly when the battery is almost full, it’s a waste of time to sit and wait for the battery to fully charge. For example, it may take the same amount of time to charge from 10 to 80 percent as it does from 80 to 90 percent. When traveling in an EV, it is more time efficient to stop more often for less time.

For the charge test, we record the charge rate and charge status of the battery every minute and how many minutes (or hours and minutes) it takes to complete the test. The most interesting and comparable detail is the average fill rate during the entire test, but it is also a technological advantage to have the highest peak. In addition, the amount of energy put into the vehicle versus how much the battery contains allows us to calculate the losses incurred during fast charging.

Learning the ins and outs of EVs continues to be incredibly exciting, and no matter how the auto industry evolves, we’ll find ways to test any vehicle that hits our path.

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