Pollution from tire wear can be 1,000 times worse than a car’s exhaust emissions, Emissions Analytics has found. Emissions Analytics is an independent global testing and data specialist for the scientific measurement of real-world emissions and fuel efficiency for passenger and commercial vehicles and non-road mobile machinery.

Harmful particulate matter from tires—and also brakes—is a growing environmental problem, and is being exacerbated by the increasing popularity of large, heavy vehicles such as SUVs, and growing demand for electric vehicles, which are heavier than standard cars because of their batteries.

Source: California Air Resources Board (ARB)

Vehicle tire wear pollution is completely unregulated, unlike exhaust emissions which have been rapidly reduced by car makers due to the pressure placed on them by European emissions standards. New cars now emit very little in the way of particulate matter but there is growing concern around non-exhaust emissions (NEEs).

Non-exhaust emissions are particles released into the air from brake wear, tire wear, road surface wear and resuspension of road dust during on-road vehicle usage. No legislation is in place to limit or reduce NEE, but they cause a great deal of concern for air quality.

NEEs are currently believed to constitute the majority of primary particulate matter from road transport, 60% of PM_2.5 and 73% of PM₁₀. In the 2019 report ‘Non-Exhaust Emissions from Road Traffic’, the UK Government’s Air Quality Expert Group (AQEG), recommended that NEE are immediately recognized as a source of ambient concentrations of airborne particulate matter, even for vehicles with zero exhaust emissions of particles—such as EVs. (Earlier post.)

To understand the scale of the problem, Emissions Analytics performed some initial tire wear testing. Using a popular family hatchback running on brand new, correctly inflated tires, it found that the car emitted 5.8 grams per kilometer of particles.

Compared with regulated exhaust emission limits of 4.5 milligrams per kilometer, the completely unregulated tire wear emission is higher by a factor of more than 1,000. Emissions Analytics notes that this could be even higher if the vehicle had tires which were underinflated, or the road surfaces used for the test were rougher, or the tires used were from a budget range—all very recognizable scenarios in real-world driving.

The challenge to the industry and regulators is an almost complete black hole of consumer information, undone by frankly out of date regulations still preoccupied with exhaust emissions. In the short term, fitting higher quality tires is one way to reduce these NEEs and to always have tires inflated to the correct level.

Ultimately, though, the car industry may have to find ways to reduce vehicle weight too. What is without doubt on the horizon is much-needed regulation to combat this problem. Whether that leads to specific types of low emission, harder wearing tires is not for us to say—but change has to come.

—Nick Molden, CEO of Emissions Analytics