How electric vehicles impact tire design | 2021-05-07

The United States is the world’s third largest electric vehicle (EV) market behind China and Europe. More than 1.74 million plug-in light electric vehicles have been sold in the United States since 2010. Electric vehicle registrations in the United States reached a record market share of 1.8% in 2020, according to IHS Markit.

While still representing a relatively small percentage of all personal vehicles sold in the United States, the number of electric vehicles on American roads is expected to multiply over the next several years as governments and automakers pursue electrification, while the historic barriers to widespread acceptance of electric vehicles – including “range anxiety” and high retail prices – are diminishing in importance. (IHS Markit estimates that electric vehicles will account for 3.5% of light vehicles sold in the United States by 2021 and more than 10% by 2025.)

This change presents challenges for tire dealers, who will need to know how to maintain electric vehicles, and for tire manufacturers, who design and manufacture tires specifically tailored to the design and performance of electric vehicles.

The differences between current electric vehicles and traditional gasoline vehicles are significant. Electric vehicles are generally heavier than their counterparts equipped with an internal combustion engine. They generate more torque and less noise. And the range of electric vehicles is not always comparable to what a gas tank can provide, although OEMs are working hard to extend range limits. (General Motors announced last month that it was developing an all-electric version of the Chevy Silverado pickup that will have a range of 400 miles.)

MTD recently spoke with tire manufacturers who have an original equipment presence in the United States to find out how electric vehicles impact the design and construction of tires.

A matter of weight

Electric vehicles are generally heavier than comparable gasoline cars. (The Tesla Model 3 sedan tips the scales at around 3,500 pounds. The Honda Civic sedan, a similarly sized car, weighs around 2,900 pounds.)

“Due to the weight of their batteries, the overall weight of the electric vehicle tends to be heavier,” says Richard Smallwood, CEO and President of Sumitomo Rubber North America Inc. fully – but today the weight difference is around 15 to 20%, depending on the vehicle model.

“As we know, heavier vehicle weight negatively impacts tire life and the handling characteristics of the tire / vehicle combination,” he says.

Robin Wilkes, vice president of original equipment, Pirelli Tire North America, says tire manufacturers “must ensure that tires of the same size have the capacity to carry the extra weight” of electric vehicles. “Sometimes this can be done by changing the size of the tire. But beyond that you have the designation of high load capacity (tire), which is spreading in Europe and which we really didn’t need in the past.

“Electric vehicles push the boundaries of tire design in terms of load capacities,” says Mauricio Mendez Sotelo, head of technical product management, research and development, passenger and light truck tires, Continental Tire the Americas LLC .

“The tires have to be able to withstand higher loads and require higher inflation pressure to support that load. Original equipment manufacturers are asking, “How can we make tires with the dimensions we currently have that can withstand a higher load, without building bigger tires?” ”

“The vast majority of EV tires on the market are currently in XL sizes to accommodate the increased load,” says Ben Patel, senior vice president and chief technology officer, Cooper Tire & Rubber Co. “And some manufacturers have announced their intention to start manufacturing Tires designated “HL” for even more capacity. This requires a more robust and heavier construction.

Instant torque

“Another interesting thing about electric vehicles is the instantaneous torque ‘they create’ and the fact that electric vehicles can generate 100% of their torque at zero rpm,” says Dale Harrigle, chief engineer for the development of products, consumer replacement, Bridgestone Americas Inc.

“There is a lot of work going on on tire wear – first of all, understanding the implications of electric vehicles on wear and also how we adjust the construction and models of the tires to give customers the longest life. life they are used to.

“In addition, the braking characteristics (EV) are slightly different from those of conventional vehicles equipped with conventional brakes,” he says. “We need to understand how all of these factors affect wear over the life of the tire. I think a lot of things will depend on the material technology and the tread technology. ”

Thomas Kenny, senior director of research and development at Yokohama Tire Corp., says that a 20% loss of tread wear “is not uncommon” with high torque electric vehicles.

“Tires used for EV applications will require a paradigm shift in the way they are designed if they are to perform at a level comparable to their non-EV counterparts. This includes a stiffer tread block design, the use of a more rugged construction, and in some cases new compound technology.

Cut the noise

The lack of gasoline engines and all the sounds they make mean EV tires have to be designed to make even less noise than usual.

“Weight and torque are definitely the issues you hear about the most” when EVs are discussed, says Aaron Neumann, director of product development at Nexen Tire America Inc.’s technical center.

“But those are probably not our two main concerns. As we develop tires for electric vehicles, we place more emphasis on noise and vibration. If you’ve had the chance to drive an electric vehicle, you’ll know how smooth and quiet it is.

“The electric motor doesn’t produce near the vibration of the internal combustion engine, which has masked noise and vibrations from other parts of the vehicle for quite some time,” notes Neumann. “Any noise or vibration from the tire is more pronounced” in an electric vehicle.

“Noise is probably more annoying” for electric vehicle owners than for traditional car owners, according to Rodrigo Uso, senior account technical director and technical sales team leader, North America, Hankook Tire America Corp.

For EV drivers, “tire noise is becoming very important and manufacturers look at noise from a different perspective,” he says.

Some unique technologies have been introduced to electric vehicle tires, including a foam absorber – roughly a piece of foam that is attached to the inside of the tire that will help absorb noise from the cavity.

Within reach of

Low rolling resistance tires are normally associated with gasoline vehicles. But in order to maximize battery life, electric vehicles also require low rolling resistance tires, according to Rick Cunat, general manager of Kumho Tire USA Inc.’s technical center for the Americas.

“For tires, the main source of drag is rolling resistance. In addition, the aerodynamics of the tire contributes to the overall drag of the vehicle.

“There are many ways for tire manufacturers to approach rolling resistance through innovative materials and the shape of the tire cavity to maximize all of the performance attributes demanded by electric vehicles. “Consumers” are looking for range and tire life. That’s the whole game.

“The focus on tire performance has been high” by electric vehicles, says Steve Calder, technical marketing manager, Michelin North America Inc. “Typically with an internal combustion engine, about 20% of fuel consumption of fuel is used to overcome rolling resistance. of the tire, so any improvement we can make in rolling resistance has a direct impact on the vehicle.

The same principle applies to electric vehicles, he adds. “You can (gain) range if you put on a tire with very low rolling resistance compared to a traditional tire. “

Down the road

As tire manufacturers continue to perfect the technology and design of today’s electric vehicle tires, they also look to the future.

“If you look at how the tires perform today compared to 20 years ago, we’ve made huge gains,” says Smallwood of SRNA. “The thresholds continue to climb. Twenty years from now, electric vehicle tires will likely be better than our most maneuverable tires today. ”

Tire dealers should also be aware that the number of EV tires available in the replacement channel will increase over time, says Conrad Galamgam, vice president, product planning and technical services, Toyo Tire USA Corp.

“With the proliferation of electric vehicles over the next decade, it will be more important than ever to monitor new tire sizes, higher load capacities and ideal performance to meet the demands of these new vehicles and improve performance. electric vehicle experience. ”

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About Mohammed B. Hale

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