How do I know what range my electric car is?

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Electric vehicle (EV) range is one of the key measurements that often drives shoppers from one vehicle to another. How exactly does the EPA calculate driving range, and should it be your top criteria when choosing a battery-powered automobile?

Two Main Driving Tests

Similar to how fuel efficiency is tested for gasoline and diesel-powered vehicles, the Environmental Protection Agency (EPA) determines the range of an electric car, truck, or SUV by running it through a series of tests, or 'schedules,' on a dynamometer that simulate real-world driving conditions.

There are two key tests in particular: the Urban Dynamometer Driving Schedule (UDDS), and the Highway Fuel Economy Test Driving Schedule (HWFET), which stand in for city and highway driving, respectively. Starting with a fully-charged battery, an electric vehicle sits overnight and is then run repeatedly through the UDDS until the battery is drained completely of energy. It is then charged again to run through the multiple HWFET tests until empty. The miles that the vehicle travels during each test serve as its initial range estimate for the highway and city driving cycles. It's also possible for automakers to choose a more complex series of driving cycles as an alternative when generating this number.

Why “initial?” The EPA recognizes that its tests are performed at room temperature in a laboratory, which can't account for the variety of weather and environmental conditions that EV drivers might encounter in the real world, and the agency considers that original mileage number artificially high as a result. The preliminary numbers are multiplied by 0.7 and then weighted for highway (55%) and city (45%) to achieve the official range number.

MPGe Is Important, Too

There's an important second step in the EPA range evaluation process. After an EV's battery is drained, it's charged back to 100% while a meter monitors exactly how much energy (measured in kilowatt-hours) is used. Those kilowatt-hours are divided by the mileage traveled during the test to reflect the energy used per mile of driving.

On the window sticker, however, the big number is MPGe (the “e” is for “equivalent”), while kilowatt-hour per 100 miles is listed in smaller print. The EPA considers one gallon of gasoline to be the energy equivalent of 33.7 kilowatt-hours of electricity: if a car uses 33.7 kilowatt-hours of electricity to travel 75 miles, then it receives a rating of 75 MPGe.

Comparing One EV To Another

Why is MPGe a more effective tool when comparing one EV's efficiency to another, rather than simply relying on range? EV range is typically a function of battery size, with larger, heavier vehicles able to accommodate bigger batteries that can store more energy. The Ford Lightning full-size truck, for example, can travel up to 320 miles on a single charge, versus the compact Chevrolet Bolt EV hatchback which offers 259 miles of range.

MPGe shows buyers the huge differential in efficiency between these two models, which is tied directly to the extra weight of the pickup. The Bolt EV is rated at 120 MPGe, while the Lightning manages no better than 70 MPGe. In terms of actual energy costs, the Chevrolet will cost almost half as much as the Lightning to drive the same distance.

Real World Variables

Remember, your real-world EV driving range might be greater or less than a vehicle's official EPA rating. Extreme heat and cold, hilly terrain, and higher cruising speeds can all impact how far an electric vehicle travels on a single charge. If you think of the window sticker as a guideline, rather than a guarantee, you'll have a better idea of how far your EV can travel on a full battery.

Guest post: Blane Erwin, Current Automotive

Above: Tesla's Model Y (Photo by Casey Murphy, EVANNEX

Range gets headlines. It earns automakers bragging rights, or gives their competitors mocking rights. Range is what determines whether or not an electric vehicle will fit into someone’s lifestyle. Short range EVs like the 84-mile Fiat 500e serve as great commuters, while long range 200+ mile EVs can do (pretty much) anything a gas car can do better.

In the United States, the Environmental Protection Agency is responsible for testing and rating the fuel economy of all road-going vehicles, and the methodology used for rating electric vehicle range is actually very close to what they use to test conventional vehicles.

THE DYNAMOMETER AND DRIVING CYCLES

The EPA tests cars on a dynamometer, also known as a dyno. A dyno is kind of like a treadmill for cars – the car is placed on rollers so the car can be “driven” while staying locked in place. Dynos can be used to gather all sorts of data about a car’s performance, such as horsepower and fuel economy. The EPA is obviously more interested in the latter.

On the dyno, vehicles are put through different driving cycles, where the cars are sped up or slowed down to hit prescribed speeds to simulate different kinds of driving. The two important cycles that EVs are put through are the Urban Dynamometer Driving Schedule (UDDS) and the Highway Fuel Economy Driving Schedule (HWFET).

The UDDS cycle simulates stop-and-go city driving by getting the test vehicle up to speed and back down to zero. It’s used to measure city fuel economy.

Above: Target speeds during the EPA’s UDDS test (Source: epa.gov)

The HWFET cycle simulates sustained-speed highway driving by getting the vehicle up to speed, then having it fluctuate between various speeds in the 30 – 60 mph range over the course of the test. The wheels don’t come to a complete stop until the end. This test measures highway fuel economy.

Above: Target speeds during the EPA’s HWFET test (Source: epa.gov)

RATING ELECTRIC VEHICLE RANGE

The best EPA test for measuring electric vehicle range is known as the Multi-Cycle City/Highway Test Procedure. For this, the EPA will fully charge a vehicle, leave it parked overnight, and put it on the dyno the following morning.

The electric vehicle is then put through multiple UDDS and HWFET cycles until the battery is completely discharged and the car can no longer drive. The dyno measures how many miles the EV “travels” during testing to provide a preliminary range number.

The car is then plugged in with the charger provided by the automaker and charged back to full. The charger is on a meter to precisely measure how much electricity the charger draws during charging – including electricity lost to inefficiency. Then, the EPA does some math to determine the efficiency of the vehicle, measured in Miles per Gallon equivalent (MPGe).

The numbers from the closed-environment test at room temperature and relatively low speeds typically overstate the amount of range and efficiency an electric vehicle would see in real-world use. For example, the Tesla Model Y will travel 451 miles on the Multi-Cycle City/Highway Test Procedure – which is a much higher range than anyone would actually see driving the car in normal conditions. The EPA will multiply the preliminary range and efficiency numbers from the tests by 0.7 to provide a final rating more in line with what drivers can expect from their cars. For the Model Y, that’s 316 miles of range.

At the end of the day electric vehicle range ratings are an estimate, just like MPG numbers are just estimates for gas cars. The EPA and automakers can’t guarantee that any given driver of any given car will experience the rated numbers. More aggressive drivers will be less efficient and see less range as a result. Electric vehicles won’t go as far in cold weather either.

The important thing is to get an electric vehicle with enough range to fit your driving needs. Whatever those needs may be, there’s an EV out there that will meet them.

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Source: Current Automotive; Editor's Note: Current Automotive is the first-ever U.S. car retailer focused exclusively on used electric cars launched by two former Tesla employees.