New York - When Bryan Nakagawa purchased an Audi E-tron in 2018, he fell in love with the car’s interior and handling, the space for his kids and surfing gear and, of course, its small carbon footprint. But the Salem, Oregon dentist soon discovered that his affection was fleeting – it flew away right around 70m/h (113km/h).
“I wouldn’t even drive a mile and I’d lose like three miles off the estimated range,” Nakagawa says of cruising the interstate in his electric Audi. “It always made me nervous.”
In January, Nakagawa traded in his E-tron for a hybrid, the Jeep Grand Cherokee 4xe. Now he gets 40km of electric driving, enough to run around town, plus a petrol-engine back-up for any longer, higher-speed journeys.
All over the world, EV fever is running high, but battery-powered vehicles are underperforming against expectations in one critical place: highways, the most fraught part of electric driving and one of the biggest hurdles to mass EV adoption.
As a crowd of buyers like Nakagawa are finding out the hard way, speed is a particularly relentless range-killer. Blame the laws of physics, the US federal government or both.
When deciding which electric car to buy, consumers in the US typically refer to a range estimate provided by the Environmental Protection Agency, treating it as something of an efficiency North Star, just as gas-guzzlers can be loosely categorised by miles per gallon.
The EPA arrives at its figure after a vehicle is tested in two ways, one on a prescribed schedule intended to replicate a highway trip and another as a proxy for the type of city miles one might log running errands or picking up the kids at school.
In determining its final range estimate, however, the government puts slightly more weight (55%) on how a vehicle performed in the city portion of the test. Nor do any EPA tests push cars faster than 96km/h, a figure out of step with vast stretches of freeway in most parts of the world.
“The EPA range is for the most part pretty good if you just drove a steady 65 miles per hour (105km/h),” says Jake Fisher, the senior director of vehicle testing at Consumer Reports. “But not everybody drives like that.”
The disconnect is exacerbated because electric vehicles, unlike petrol-burning machines, get more efficient in cities. Thanks to regenerative braking systems that recharge the battery while slowing down the car, carmakers tend to ace the urban part of the range test. In the right neighbourhood or even when plodding through a halting commute, an electric car will travel much farther than its EPA seal states.
At the other end of the speed spectrum, however, engineers can’t do much to change the laws of physics. Because the amount of air resistance an EV needs to overcome compounds as the car speeds up, the amount of battery required to go a certain distance does not increase linearly with speed. Travelling at 65mph (105km/h), compared with 55mph (88km/h), for example, will cut range by 28%, according to Lennon Rodgers, a University of Wisconsin engineering professor.
Bumping up to 75mph (120km/h) chews up 38% of range, all else being equal. The speed tax is particularly pronounced with blocky trucks and SUVs.
“I like to say you can go far or you can go fast; you can’t do both," says Tom Moloughney, a motoring journalist who runs a YouTube channel on EV efficiency, State of Charge.
Many of Moloughney’s days are spent on the New Jersey Turnpike, holding a steady 70mph (113km/h) until the particular vehicle he is testing is wrung out. Invariably, when he finally limps up to a charging port with his EV on empty, the machine has travelled far fewer miles than its EPA-certified estimated range.
“Honestly, if it gets its range rating,” Moloughney says, “it’s a major win for the car.”
One exception: the Porsche Taycan. Moloughney says it consistently achieves more miles than its range estimate, even on the interstate, in part because it’s so aerodynamic. Teslas are on Moloughney’s naughty list: He says they consistently under-perform range estimates on the interstate by 10% to 12%.
The EPA admits that its oversight is imperfect. A spokesperson said the certifications were “a useful tool for comparing the fuel economies of different vehicles, but are not going to be an exact measurement”.
The agency’s tests also fail to capture a slew of other range-killers, including aggressive driving, off-road tyres, cold weather and heating and air conditioning use, to name a few. The EPA has an admittedly imprecise way to account for the handicaps: a blanket reduction of its final estimate, usually by around 30%.
Regenerative braking is another wild card. If a car has a default setting for regenerative braking, that’s what the EPA will use on its tests. Consequently, a driver who shuts the system off will see worse real-world results, while someone who dials it up may outperform estimates.
Rodgers, who has studied battery-powered range for more than a decade, offers straightforward advice for EV rookies: Trust the car. Range estimates displayed by the vehicle itself are likely to be more accurate than the EPA’s, and they also improve over time as the car’s algorithms build a data library of individual driving style and climate-control settings.
“Eventually, people usually just… make their own calculations,” Rodgers says.
Granted, none of this matters for the average commute. All but two EVs on the US. market have range ratings over 200 miles, meaning daily EV drivers don’t need to factor in a speed tax. Petrol-powered vehicles aren’t exempt from the laws of physics, either; they clock similar efficiency losses at speed and lose mileage in city driving as well.
But as EV adoption climbs, EV rookies are probably in for a road-trip surprise in coming months. Moloughney, for one, thinks it’s time for the EPA to overhaul its process and build a faster, more idiosyncratic regimen.
“I try to tell people not to stress too much, but I like them to understand how it all works,” he says, “because a few days a year, they’ll really need to.”
Bloomberg