Electric vehicles produce less non-exhaust particulate than ICEs

Motoring organisation RAC has moved to “set record straight” following controversial remarks from Environment Secretary George Eustice that electric vehicles (EV) may not be as green as people think. In order to do that the RAC, which wants to speed up EV take-up, commissioned battery electrochemist Dr Euan McTurk to address the suggestion that EVs produce more particulate from brake and tyre wear than their petrol and diesel counterparts.

Here’s how the controversy came about. In 2019 government advisory body The Air Quality Expert Group published research suggesting that as electric vehicle (EV) take-up increases, the proportion of particulate matter emissions (specifically PM2.5 – which includes those generated by brake and tyre particulate) will increase. Since that part of the report referred to particulate matter as opposed to carbon dioxide and nitrous-oxide emissions – which of course internal combustion engines (ICE) will always emit to one degree or another, but tyres don’t. It was a logical observation to make, but seems to have been illogically seized upon by subsequent reports published by third parties.

For example, Emissions Analytics suggested that particulate matter pollution from car tyre wear is 1,000 times higher than car exhaust emissions, and that car tyres may produce as much as 9.28 grams of particulate matter per mile. However, according to the latest RAC report “some common-sense calculations show that this couldn’t possibly be the case”.

The problem is that by early February 2022, Environment Secretary George Eustice told MPs on the environment, food and rural affairs select committee that the environmental gains of moving from ICE to battery-powered EVs, “may be less than some people hope”. His argument was that since electric vehicles can weigh up to 30 per cent more than an equivalent petrol or diesel car, their usage would result in greater wear of EV brakes and tyres and thus more particular: “The unknown thing,” he said, “is how far switching from diesel and petrol vehicles to electric vehicles will get us. There’s scepticism, as some say that [due to] wear and tear on the roads, as these vehicles are heavier, the gains may be less than some people hope, but it’s unknown at the moment.”

Non-sensical calculations

Here’s how Dr McTurk counter that suggestion in RAC’s report: “A typical 16-inch family car tyre weighs around 9 kilograms, so four of them on a vehicle gives a total

weight of 36 kilograms. That’s not just the tread, but the full tyres. If the car really did shed 9.28 grams of particulate matter per mile from the tyres, then the car tyres would physically have disappeared – and the car would be running on its alloys – in less than 4,000 miles.

“In reality, the tread of a tyre is about 35 per cent of the tyre’s total weight, so the tyres would be bald in less than 1,358 miles, or two months’ worth of driving for the average UK driver. Chances are that the Emissions Analytics study was accidentally measuring particulate matter emitted by other cars, that had settled on the road and then been kicked up by the tyres of the test car, rather than what was being shed from the tyres of the car undergoing the test.”

And thus this particular conclusion found in the emissions analytics report can be dismissed. But if electric vehicles are heavier than petrol or diesel cars, do they wear out their tyres faster? Here’s Dr McTurk’s answer:

“Firstly, modern electric vehicles aren’t actually that much heavier than many modern petrol or diesel cars, especially with the recent trend towards bigger and heavier SUVs…[and secondly] very soon we will likely start to see a move away from stuffing more battery capacity into the same space, towards offering the same capacity but in a lighter, cheaper battery, resulting in a lighter, cheaper car.”

In order to address the EV tyre wear point, the RAC’s report spoke to James Rooney, fleet engineer at British Gas, which currently operates 800 electric vans, but will soon run thousands. For obvious practical reasons these electric vans are large, heavy vehicles with traditionally tyre-chewing front wheel drive. However, even these have achieved 15,000 miles and not needed tyres or brakes replaced from wear. And therefore they have gone nearly three-times further than the emissions analytics data suggested they should.

In addition, the RAC offered a second example relating to Ryan Todd’s fleet of Nissan LEAF electric taxis. These come fitted with Michelin tyres that usually last between 30,000 and 36,000 miles on the rear wheels, with the fronts lasting 20,000 miles. Ryan noted that his diesel taxis do tend to get an extra 5,000 to 10,000 miles of lifespan out of their front tyres (LEAFs are not just front wheel drive).

However, the 30,000 to 36,000-mile lifespan of the rear tyres on his LEAF

taxis is about the same as the rear tyres on his diesel taxis, since they aren’t propelling or steering the vehicle.

Since most of the braking in electric cars is done via regenerative braking where the electric motor works in reverse, (resulting in vastly reduced brake wear) and since the studied EVs offer similar tyre wear on the rear wheels in particular, the situation actually bodes well for controlling particulate matter pollution.

Remapping the throttle of EVs to reduce the aggressiveness of the power delivery, would also help to extend tyre life.

In addition the report notes that tyre manufacturers are also tuning tyres to electric vehicles. “This includes both big name tyre brands and new companies, like Enso, that have been set up specifically to tackle pollution from tyres.”

And therefore, the environment secretary is just plain wrong. As the RAC report concludes “electric vehicles already vastly reduce particulate matter from brake wear, and claims of tyre wear contributing 1,000 times the particulate matter pollution of petrol and diesel exhausts are greatly overexaggerated”. Rather, with the currently technology fleets are already seeing brake lifespans increased fourfold and tyre wear broadly on par with petrol and diesel cars. Future advances in EV propulsion and tyre design is only likely to improve this.

You can download the complete RAC report here.