Electric Cars Have a Big Tire Conundrum
[Stay on top of transportation news: Get TTNews in your inbox.]
The Lucid Air Dream Edition travels up to 520 miles on a charge, more than any electric vehicle on the market by a wide margin. If a buyer chooses the larger, 21-inch wheels, however, 39 of those miles vanish — a 7.5% range penalty.
To be fair, the bigger shoes do look cool, and they’ll still take you nonstop from New York to Cleveland. But when it comes to wheels and tires — where the rubber literally meets the road on electric vehicle range — there’s an escalating battle between physics and aesthetics. More often than not, the latter is winning, as the people who buy EVs (and the people who make them) choose bigger, stickier, “spokier” options that prize looks and performance over efficiency.
“Everything is about range, so the slipperier you make it, that’s great,” says Richard Scheer, exterior design director at Chevrolet. “But even in the EV world, people will trade off range for cool wheels.”
The physical recipe for an ultra-efficient tire is pretty simple: skinny (so it blocks less air), small circumference (so it takes less energy to turn), a compound that doesn’t stick overly much and a hub cap that is mostly covered (to cut down on air turbulence inside the wheel).
But auto executives and engineers must layer in a dizzyingly complex series of compromises when outfitting a car in reality. For every bit of size and/or stickiness, the vehicle sacrifices mileage and efficiency. That’s also true for gas-burning machines, but electric cars are typically far heavier than similar-sized internal-combustion cars, meaning their tires have to withstand more pressure and wear. They are also far quieter, so tire engineers agonize over noise — going so far as to pump acoustic foam into the rubber cavity.
“You get into a complicated balance,” said David Van Emburg, executive vice president of automotive original equipment global sales at Michelin.
In short, a tire built for range looks a lot like the one that comes standard on the Chevrolet Bolt — a Michelin Energy Saver on a 17-inch wheel with a swirly center of spokes — and nothing like the massive, knobby tires on the GMC Hummer EV that Scheer helped design. “Those are just cool wheels,” he explains. “We’re showing that when you get to EV, you can still have fun products.”
The North Star for tire efficiency is something called rolling resistance, which is exactly what it sounds like — a measure of how much the circle sticks to the ground (picture a bowling ball and a medicine ball racing across a gym floor). An increase in tire size can actually lower resistance, as it spreads the weight of the car more widely and “squishes” less, but supersizing presents another, often greater problem: The increased mass requires more energy to get going.
The BMW i4 M50, for example, a souped-up version of the marque’s newest electric sedan, travels 271 miles on a full charge with its standard 19-inch performance tires. On high-performance 20-inch wheels, however, it makes only 227 miles — a 16% handicap. Ford likewise concedes that its Mustang Mach-E would go slightly farther if it chose tires that didn’t corner as well, and its F-150 Lightning could stretch a few more miles on rubber less suited for off-road driving.
“Those big tread patterns squabble — they move around — and don’t return all the energy you give them,” says Chris Allard, chief engineer of Ford’s underbody systems engineering. “You’re making a conscious trade-off there.”
For now at least, the no-compromise strategy is what car buyers want, particularly as the EV market transitions from early adopters to the mass market. Across Lucid’s spectrum of models, customers generally opt for the bigger wheels, shortening their time between charges by up to 9%. Four out of five customers for Hyundai’s hot new Ioniq 5 opt for the larger wheel. Similarly, 40% of folks sliding into Volkswagen’s ID4 choose the 20-inch rims over the 19. At Polestar, only about one-third of buyers opt for the standard 19-inch wheel with a summer tire; the rest check the box for a 20-inch wheel that sacrifices about 5% of the car’s range.
Siamak Azmoudeh of SkyBitz discusses the rise of the smart trailer and why the industry standard is shifting toward more sensors, more data and more business intelligence. He joins host Seth Clevenger to explain the evolution of trailer telematics. Tune in above or by going to RoadSigns.ttnews.com.
“It’s kind of a look,” says Polestar engineer Glenn Parker. “We’ve seen tires get bigger and bigger and bigger over the years. ... And as a performance brand you can’t just say ‘What’s the most efficient tire we can put on the car?’ ”
Ford wanted to instill a notion of “no trade-offs” with its Lightning F-150 pickup truck, so the rig comes standard with rugged tires, even though they aren’t the best for range.
Tire longevity isn’t entirely out of drivers’ hands. Ford’s Allard says it’s important to pay attention to the tire monitoring gauge and keep tires filled to the right air pressure. “If you’re a cheap guy like me, you keep that screen up,” he says.
But Big Tire is also hustling to make larger, stickier tires stretch a little farther on the road. In the past 20 years, Michelin has managed to improve tire efficiency by 20% without sacrificing stickiness and performance, according to Emburg. To get there, its engineers tinkered with tread patterns, the thickness and chemical composition of the rubber and the patterns of steel belts holding the whole package together.
“I’ve been in the game 34 years and we’re still looking at major steps in technology,” he says. “We’ll optimize every part of the tire for its mission.”
Car companies are iterating, too. At the moment, the hub of the Polestar 2 wheel looks a little bit like a four-leaf clover, but it has been reworked for next year’s model. The new version has far less open space, with five triangles poking toward the center like pieces of aluminum pie. The result: an extra two or three miles of range, even on the 20-inch wheels.
Want more news? Listen to today's daily briefing below or go here for more info: