In 1845, somewhere between inventing a system for detonating explosives by electricity and the refillable fountain pen, Robert Thomson, a Scottish engineer and entrepreneur, patented the first pneumatic tire—a then wondrous, now everyday item that has been gradually evolving ever since.
Now, in the era of electric vehicles, they are more in focus then ever before. On the one hand, while passenger safety remains a priority, the right tires can have a significant effect on efficiency—and thereby the range of your EV—but on the other they’re also a source of noise and pollution.
Since the traditional global tire market is worth well over $200 billion, and 2.5 billion tires are sold a year worldwide, manufacturers are rubbing their hands at the coming death of pure combustion cars, and gearing up for a battle to fashion the ideal balance of eco credentials, performance and efficiency that will create the perfect EV tire. Whoever wins will secure quite the prize.
Rolling Resistance or Longevity?
Range optimization has been the primary concern so far. According to Michelin, the efficiency difference between good and bad tires can be as much as 7 percent. Better tires reduce rolling resistance, meaning a car will coast further before coming to a stop. It will therefore need less energy to travel the same distance. A 7 percent increase in efficiency will give an EV that much more range—so, if it could go 300 miles with a poor tire, it will travel 321 miles with a good one.
“There are several tire components that can influence rolling resistance,” says Thomas Wanka, principal technology development engineer at Continental, a company that has been exploring EV tire design through its association with electric motorsport series Extreme E. “These include the rubber compound and the tread.”
Manufacturers are experimenting with nanomaterials in their tires, such as nanocarbon and nanosilica, to improve performance, traction and durability. There is also research into bio-based alternative compounds such as guayule and dandelion rubber.
You can reduce rolling resistance by reducing tread depth, but this also means the tire won’t last so long and produces increased noise. Continental, however, thinks it has the answer. “We have developed special soft rubber compounds that allow us to reduce rolling resistance and noise at the same time without sacrificing mileage,” says Wanka.
“The tire industry often argues that improving one metric, like efficiency, means sacrificing another, such as durability or wet grip,” says Gunnlaugur Erlendson, CEO of ENSO, a startup tire company focused on optimizing for EVs. “But the huge differences between premium and budget tire performance prove that the technology already exists to make tires better overall. The transition to EVs has made improving efficiency, durability, and tire pollution more critical than ever.”
The Problem With Particulates
Pollution has also come into focus with the growing concern about the environmental impact of transportation. Electric vehicles produce no tailpipe emissions, but that doesn’t mean they produce no emissions whatsoever. While the theory that their additional weight increases brake dust is a myth (braking typically comes through regeneration rather than friction on EVs), tire particulates from wear are a different matter. Research by Michelin claims that, on average, EVs have 20 percent more tire wear than comparable internal combustion engine vehicles.
This data has been immediately seized upon by those looking for reasons to denigrate EVs, claiming that electric cars could be worse for the environment than diesel-powered ones. Michelin argues that its figure of 20 percent more tire wear in EVs comes from their extra weight, greater motor torque, and the way regeneration tends to reduce the amount of coasting. But manufacturers hope to counteract the particles deposited by tires by making them last longer.
There can be a huge variation in durability between tire brands, which affects how much rubber they lose in use. According to Michelin, a set of four of its CrossClimate 2 tires sheds 1.5 kg of material during 20,000 km of travel, whereas the industry average is 3.5 kg, and the worst brands can produce as much as 8 kg. Michelin claims that this is because of the “self-adapting technology”of CrossClimate 2 tires, which is designed to adjust to road temperature. The company has also devised a more resilient compound, while the tread pattern itself distributes pressure across the tire surface contact area, again reducing wear.
However, it’s tricky directly comparing the pollution from particles shed by tires to exhaust fumes from an internal combustion engine. Even though 1.5 kg of rubber particles still sounds bad, there is a significant difference between particle sizes. The major culprit for public health is NOx, which causes smaller particulates in the “PM2.5” category (meaning the particles are 2.5 microns in diameter). For tires, only 1 percent of particulates are below PM10 (10 microns), and 0.2 percent PM2.5 or below. Most PM2.5 pollution in urban areas still comes from vehicle exhaust NOx.
Unfortunately, there is scant research into the health effects of tire particulates. One of the few comprehensive studies was completed more than a decade ago, in 2012. “At that time, it was not decided that it was the priority subject,” says Gary Guthrie, SVP, Michelin. “The priority subject was more understanding the fate of particles in water and how they degrade.”
“Studies sponsored by the Tire Industry Project (TIP) of the World Business Council for Sustainable Development (WBSCD) have indicated that tire and road wear particles (TRWP) do not pose risk to human health,” says Wanka. “Inhalation studies suggest that TRWP is unlikely to pose risk to humans through airborne exposure.”
“Tire pollution and NOx emissions are different,” says Erlendson. “NOx is a gas byproduct of fuel combustion, while tire particulate matter is a solid pollutant, akin to dust from wood burners. Unlike NOx or CO2 from tailpipes, however, there are no global regulations currently in effect that specifically limit tire pollution.”
Are Biodegradable Tires the Answer?
Biodegradable tires look like a potential solution to tire pollution. However, there are some paradoxes with this idea. “Tires are safety relevant,” says Wanka. “They are the only contact between a vehicle and the road. Hence it is crucial that no degradation of a tire occurs until the end of the use phase.” For many tires, the lifespan could be five years or more.
“While the tire industry is increasingly exploring bio-based materials, such as natural rubber, tires themselves, and the pollution they generate, are not yet biodegradable,” says Erlendson. “A tire that biodegrades on the vehicle would not be good for durability. However, it would be beneficial if the tire particles that shed during driving could biodegrade in the environment, preventing them from accumulating in our air, land and oceans.”
“Our focus is on the front end rather than the back end right now,” says Guthrie. This means using more recycled materials in manufacturing, aiming for a degree of circularity. “What we would prefer to do is to be able to take the tire at the end of its life and make a new one from it, because that is even better for the planet than being able to just put it on flowerbeds. That way, we don’t have to take raw materials out of the Earth to make the tires in the first place.”
Michelin has indeed been working on biodegradable tire material, which could benefit the entire industry. However, if successful it’s unlikely that such an innovation would be made available to other manufacturers. “Sharing intellectual property is not exactly part of the Michelin culture,” says Guthrie. “What we try to do in terms of the wider purpose is to meet regulations, for example the understanding of how TRWP biodegrades in the environment. When we think something is good for the planet, and it’s not too competitive, we will share.”
A Better EV Tire Is a Better Tire
The focus on tire efficiency has concentrated on EVs, because of their need to get as many miles as possible from expensive batteries in a world where the charging network is still inadequate. But the benefits are not exclusive to electric cars.
“There is basically no difference between a conventional tire and a special tire for electric vehicles,” says Wanka. “It is more the case that certain vehicle models or classes have specific tire requirements.” Better service life, rolling resistance and rolling noise have been particularly beneficial for electric vehicles. “But all vehicles—regardless of their drive type—benefit from the technological advances.”
“A good tire should perform well regardless of the vehicle,” says Erlendson. “The tire industry increasingly wants to market its products as ‘EV capable’, but the reality is that there is not enough regulation and consumer awareness to enable consumers to make informed decisions about what’s best for their vehicles. We know that EVs place specific demands on tires. But the better technology that already exists isn’t being universally deployed for all tires, particularly in the aftermarket, which makes up 90 percent of total sales.”
Tire manufacturers are improving durability all the time, which could benefit all vehicle types. “With our new AllSeasonContact 2, Continental has been able to increase mileage by 16 percent compared to its predecessor, and at the same time reduce rolling resistance,” claims Wanka.
The competition between manufacturers to improve their tires is so fierce that during motor races where teams use different brands, companies scour the track after the event looking for rubber fragments. They then take these back to the lab to analyze, in the hopes of finding the secrets of another brand’s compound material.
However, some of the big problems with tire sustainability come from poor consumer habits, rather than the tires themselves. According to Guthrie at Michelin, many drivers remove their tires long before they legally need to. The primary concern revolves around the safety implications of a tire supposedly near the legal tread limit, such as longer stopping distances in the wet. The result is a staggering 50 percent of tires are removed before they hit 3 mm tread depth, let alone the 1.6 mm legal limit. This means 400 million tires are scrapped prematurely every year.
“Innovations are already making tires more efficient, durable, and quieter,” says Erlendson. “The technology to make better tires already exists, but it’s not being deployed universally because the industry has not been incentivized to do so.” Aside from safety, regulations so far haven’t extended to tire efficiency, longevity or noise, so only premium or specialist manufacturers are foregrounding these aspects. Cheaper brands major on value instead.
Whether EVs become the dominant type of vehicle or not over the next few years, the focus on building better tires could benefit every vehicle type. “If you can make a tire last longer, it would still last longer if you put it on a combustion vehicle,” says Guthrie.
Source : Wired
