Do Car Tyres Cause More Pollution than its Exhaust?

The pollution caused by tyre abrasion on road surfaces could be more than 1,000 times greater than that which is emitted by exhaust pipes, according to a new study from Emissions Analytics. The research, which was published at the end of January 2020, tested out a popular make and model of family car, running on brand new tyres that were inflated to the correct pressure.

Their findings revealed that the test vehicle was responsible for over 1,000 more emissions per kilometre than regulated exhaust pipe emissions. What’s more, the organisation predict that this problem will only become more pronounced as road users transition to environmentally friendly forms of transportation such as electric vehicles (EVs), which are carbon neutral in terms of their tailpipe emissions.

However, the report has provoked something of a backlash from key players in the industry, who insist that it is fundamentally flawed and provides a skewed view of tyre-tread emissions. In any case, Emissions Analytics have certainly opened up the discussion on the subject of tyre-derived pollution, given that the focus normally falls on exhaust pipes alone.

Concerning reading

In order to quantify just how big a problem pollution caused by tyres really is, the authors of the study selected a popular family hatchback (a 2011 VW Golf) and tested its emissions in worst-case scenario conditions. This included using new but low-quality tyres, loading the car heavily, driving on average road surfaces and at high speeds on a track containing sharp turns and bends.

All of these factors perhaps contributed to the dismal results produced by the test, but they still make for concerning reading regardless. Driving the circuit for 320 kilometres resulted in emissions of 1,844g, which translates as 5.8g/km. By comparison, tyre exhausts are not allowed to exceed 4.5mg/km, meaning the tyres could be responsible for as much as 1,000 times more pollution than the exhaust pipe.

This tallies with previous research, which has found that much of vehicular pollution comes from non-exhaust means. Our ever-advancing capacity for monitoring particulate matter (PM) and black carbon means that we are now able to say with confidence that 60% of PM2.5 and 73% of PM10 produced by road-based transport comes from the brakes and the tyres, as opposed to the exhaust pipe as has been traditionally assumed.

The case for the defence

The report has provoked a strong response from industry bodies, which claim that it is deliberately misleading and inflammatory. “Making sensationalist claims based on testing of a single-vehicle is not credible and, quite frankly, irresponsible,” commented Mike Hawes, who serves as the chief executive for the Society of Motor Traders and Manufacturers (SMMT).

“Emissions from safety-critical brakes, tyres and road surfaces are very difficult to measure, and a challenge already taken seriously by the sector, governments and a UN global group, which are working together to better understand, and agree, how to test them in a scientific way.” Meanwhile, the European Tyre and Rubber Manufacturers’ Association (ETRMA) were similarly unconvinced by the report’s findings, although they did welcome more research on the topic.

“Our analysis of the tyre wear rate results of Emissions Analytics’ driving test found that they do not reflect normal driving conditions and go far beyond the toughest realistic driving behaviour,” said a spokesperson. “The test conditions used a vehicle that was fully loaded with low-quality tyres. The test design incorporated high speeds and excessive cornering and underscores the unrealistic nature of the driving test and its results with an extreme driving behaviour.”