Electric vehicle tire challenges in winter
Electric and hybrid vehicles are being built and sold, worldwide, in increasing numbers, but their heavier weight compared to conventional vehicles is a challenge, particularly in winter conditions.
Electric and hybrid vehicles are being built and sold, worldwide, in increasing numbers. They have many advantages over gasoline and diesel-powered vehicles, the most important of which is no or lower greenhouse gas emissions and atmospheric pollutants.
However, electric and hybrid cars have some disadvantages compared to conventional cars, one of which is their much heavier weight. The battery pack accounts for a significant proportion of the extra weight. For example, the battery of a Tesla Model S weighs about 1,200 lbs. (544 kg). The car itself weighs about 4,940 lbs. (2,241 kg), so the battery pack is 24% of the car’s mass. Fortunately, the battery pack is in the base of the car, keeping the center of gravity low, which greatly assists handling.
Curb weight is the total weight of a vehicle and its standard equipment, but not including the driver, passengers, cargo and (sometimes) fuel. Gross vehicle weight is the total weight of the vehicle, including passengers, cargo and fuel. Curb weight includes batteries, wiring and electronics. Electric and hybrid cars have lots more wires and electronics than gasoline or diesel-powered cars. Tesla’s vision system uses a series of eight cameras and 12 ultrasonic sensors to enable semi-autonomous driving.
In general, electric vehicles also weigh more than similar gasoline-powered models. The Ford F-150 Lightning weighs about 1,598 lbs. (725 kg) more than a similar gasoline- powered F-150 truck. Similarly, the electric Volvo XC40 Recharge weighs about 992 lbs. (450 kg) more than a gasoline-powered Volvo XC40. The heaviest car on a list of almost 70 electric vehicles is the Mercedes- Benz EQV luxury passenger van, which is not far from 6,614 lbs. (3,000 kg). The Audi e-tron 55 SUV weighs 5,997 lbs. (2,720 kg).
Weight is a big issue for electric cars—the heavier the car, the less energy efficient it is, which directly affects its range. The car is more expensive since it must have more powerful brakes, suspension, wheels and tires. In general, a heavier car also is less environmentally friendly, because the brakes and tires wear out more quickly.
Reducing electric vehicle weight
Vehicle manufacturers are constantly looking for ways to reduce vehicle weight. Many electric and hybrid cars have an aluminum body attached to a titanium alloy chassis. Titanium alloys are light but sturdy, allowing protection for the lithium-ion battery pack, although more expensive. Any foreign object that punctures a lithium-ion battery would almost certainly cause a fire. An increasing number of car manufacturers are either using or developing composite materials that are both lightweight and strong. They also are becoming easier to produce, although they may be more difficult to recycle, unlike aluminum, titanium and steel.
Of the many factors which are affected by the weight of a car, its tires are very important. Tire manufacturers are responding to the increasing market demand for electric and hybrid vehicles by creating tires specifically designed for them, with an emphasis on specific features. The extra
weight leads to more rapid tire wear, so electric vehicle tires have stronger sidewalls and more robust rubber compounds. The greater mass and increased inertia mean a longer braking distance, so a focus is placed on optimal grip. The instant torque provided by an electric motor also increases tire wear and requires extra grip. With increased weight and lower emissions, never have there been greater requirements for minimal rolling resistance, so electric and hybrid vehicle tires focus on offering a smoother and more energy-efficient ride.
But probably the most little-recognized problem for tires arising from the additional weights of electric and hybrid cars involves driving in snowy and icy winter conditions. It turns out to be much easier for a driver to lose control when accelerating, steering or braking in an electric vehicle on slippery roads. Winter tires fitted to electric and hybrid cars need to have additional frictional grip compared to winter tires fitted to gasoline or diesel-powered cars.
In many northern countries, motorists usually change the tires they use in summer for tires designed to be used in winter when the roads are covered in snow or ice. In the spring, they change back. Some motorists are finding that the winter tires they have used on their gasoline or diesel-powered car are not quite suitable for their new electric or hybrid car. Although there is no category of winter tires designed specifically for electric vehicles currently, tire manufacturers have started to design special winter tires for electric cars.
Reprinted with permission from the January 2022 issue of TLT, the official monthly magazine of the Society of Tribologists and Lubrication Engineers, an international not-for-profit professional society headquartered in Park Ridge, Ill., a CFE Media and Technology content partner.
Original content can be found at STLE.
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