The coming GMC Hummer EV weighs more than 9,000 pounds and can reach 60 mph in about 3 seconds. The twin electric motors in the Ford Mustang Mach-E GT make more torque than a diesel-powered F-150 and can propel the 4,500-pound vehicle to 60 mph in just 3.5 seconds. Tesla’s Model S Plaid can reach 200 mph and hit 60 mph in less than 2 seconds.
All three deliver torque numbers usually associated with high-output diesel-powered trucks. And they are shod with tires created specifically for electric vehicles.
In the EV era, almost no part of the automobile will go unchanged — including tires. With more than 100 electric models scheduled for launch in the next few years, tire companies are under pressure as they wrestle with conflicting demands for a new generation of tires.
These new tires need to be stronger to handle increased vehicle weight and substantially greater torque created by electric motors. But the tires have to be made as light as possible to help EVs drive further between charges. They also will need to provide greater grip to keep the vehicle stable during hard acceleration. But the tread patterns will have to be quieter and generate less friction, or rolling resistance.
In addition to handling greater torque and higher loads from electric powertrains, tires on vehicles that will have some autonomous driving features are also going to be collecting and transmitting information.
“What you are starting to see is intelligence coming. So, think about a tire that is sensing something and telling it to the car or telling it to you on your app,” says Steve Rohweder, vice president of technology development at Goodyear Tire & Rubber Co.
“Maybe it is simple stuff, like it needs to be inflated. But maybe it is more detailed information, like the tire is worn out. Or maybe it is information about the road and the fact that the traction has gone away or something the car needs to know to operate in the safest condition. We do a lot of work there with sensors and integration with the vehicle. As you start to move towards an autonomous vehicle, where there is not a human and a steering wheel, those systems have to handle what the human was doing before.”
Most of today’s tires are not optimized for EVs. The weight of a battery pack often exceeds that of a conventional powertrain, and the full torque arrives at the wheels instantly and is often far higher than on internal combustion engine vehicles.
Also, tires play a key role in the overall refinement of all vehicles. On gasoline- and diesel-powered vehicles, engine sounds often mask tire and other noises. But on EVs the sounds of the tire treads on the pavement get telegraphed straight into the interior. Early efforts to combat this are somewhat crude. Tesla’s Goodyear tires, for example, have an inch of foam glued to the inside of the tire to help tamp down those unwanted sounds. It’s effective, but tire engineers are looking beyond that low-tech solution.
Engineers at Goodyear, Cooper Tire & Rubber Co., Bridgestone/Firestone, Michelin and elsewhere are designing new generations of tires that run quieter and use new low-weight, eco-friendly materials.
France’s Michelin on April 1 launched its Pilot Sport EV, a line of tires designed specifically for high-performance EVs, such as Tesla’s Model S Plaid. They use technology gleaned from the company’s experience equipping Formula E electric race cars. Pilot Sport EVs have hardened sections in the center of the tread that enhance grip. The tire also has low rolling resistance that extends driving range, Michelin says, compared with regular tires.
Japan’s Bridgestone is one of the first tire companies to start delivering lightweight EV-specific tires to automakers. The Volkswagen ID3, a Golf-sized hatchback that went on sale in Europe last fall, debuted Bridgestone Turanza Eco tires that have Bridgestone’s Enliten technology. Weight is reduced by about 20 percent, or 4.4 pounds.
“Once you make a tire lighter, you can make it more fuel efficient because of the reduced amount of material involved. And that’s something we’re going to continue to expand,” said Dale Harrigle, Bridgestone’s chief engineer for replacement tires.
Bridgestone and other tire manufacturers are using 3D-printing technology to test new tire designs and tread patterns and to make molds for testing new ideas. Harrigle said Bridgestone is using 3D technology in part to test new designs for a tire’s sipes — the grooves cut into the tread that help improve grip and reduce noise.
The Turanza tires, Harrigle explained, have noise abatement technology in their grooves. “There are little protrusions in the groove of the tire which is designed to break up the sound waves. Those are the types of technologies that we will be bringing forward into battery-electric vehicles’ tire design.”
While some EVs use off-the-shelf rubber, creating tires for the new generation of rugged, off-road electric vehicles and super- high-performance cars and crossovers presents a challenge.
Ford, for example, spent three years with Pirelli developing the tires for the Mustang Mach-E GT. Rob Iorio, Mach-E vehicle engineering manager, said engineers at the two companies often worked side by side, driving test mules, collecting and analyzing data as they worked to create a tire that best fit the DNA of Ford’s fastest electric vehicle.
The collaboration started with Ford engineers meeting with Pirelli engineers to explain their targets for the tires — including wet performance, dry performance, longitudinal and lateral performance and wear, Iorio said.
During the Mach-E GT’s gestation, “we got submissions from Pirelli. They’ll say, here’s our first set of tires and they’ll share their data. It was about managing the torque, hitting the range and being very efficient,” Iorio told Automotive News.
“The GT is all-out performance. The full torque comes on in less than 500 milliseconds, so it comes on incredibly quick and it is a very high number. We worked very closely with Pirelli to ensure the tires will grip. What we call the longitudinal mew has to be tuned to that 0 to 60 time,” he said.
Huge electric trucks, such as the GMC Hummer and Rivian’s battery-powered delivery van for Amazon, are even tougher tests for tire companies.
“They present a bigger challenge because of the added weight of the battery pack,” said Goodyear’s Rohweder. “We are seeing higher and higher load indexes requested by [vehicle] manufacturers. They want the same functionality” as internal combustion engine vehicles. The tires also have to be super-strong to stay on the rim while taking the punishment of driving over rocks and stumps and through deep, jagged ruts.
“While EVs do present some unique differences over ICE vehicles, specifically the way torque comes on and the stress on tires, the overall development and testing for tires on any of our vehicles is very similar,” said David Cowger, General Motors’ engineering and technical leader for tires. “We work closely with our tire suppliers during the development process on the various performance metrics that need to be achieved, as well as the vehicle metrics itself. As you may have noticed on the GMC Hummer EV, we have an eight-lug wheel pattern, something that you would also see on our HD trucks which make a lot of torque.”
Since 1888, when Scottish veterinarian John Boyd Dunlop developed the concept of a pneumatic tire, the main ingredient in nearly all tires has been rubber.
That might not be the case in the future. One technology to watch is Michelin’s Tweel — an airless radial tire-and-wheel combination. It’s now in production for light-duty tractors, lawn equipment and off-road recreational vehicles. Poly-resin spokes are mated to what Michelin calls a shear beam assembly, basically a mechanical spring. The one-piece Tweel bolts on to the axle.
Two years ago, GM and Michelin began working together on a version of the Tweel, called Uptis, that could be on EVs by 2024.
Other companies are looking at plastics to replace rubber.
“I think you are going to see more and more of what we call non-pneumatics, something that’s made of more of a plastic structure and has a tread to it,” said Rohweder of Goodyear. “Those are still coming along as far as being able to carry the load, achieve the speed and develop the forces, but the intent there is to create a new way of carrying the load and transmitting the forces to the vehicle.”
Airless tires still have a long way to go.
“With non-pneumatics there’s a bit of a weight penalty there and there’s still a performance trade-off. It’s not quite the same, but that technology is coming,” Rohweder says. “Could it evolve into a wheel and tire that is better than what we have at present? Potentially in the future, yes.”