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Comment by ratel | Hacker News Reader

Hold on:

The claim is this:

> "Using a popular family hatchback running on brand new, correctly inflated tyres, we found that the car emitted 5.8 grams per kilometer of particles."

It does not seem to be a mistake:

> "Compared with regulated exhaust emission limits of 4.5 milligrams per kilometer, the completely unregulated tyre wear emission is higher by a factor of over 1,000."

A tire might way up to 15 kilograms for a 20 inch type. Lets assume 10 kilograms for a normal tire which is on the high side. 4 tires is 40 kilograms. Even if we assume half of the particals are not coming from the tire (but from where?). That still leaves 40,000 / 2.9 = 13793 kilometers for the tires to be completly consumed (weighing nothing anymore). That is definitely not happening.

So without an explanation on where the matter is coming from this does not read right.

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They're torn up from the road and rubbed off from the tyres themselves. The majority is obviously coming from the road.

There's been studies done here in Sweden since we've banned studded winter tyres in some areas of Stockholm in an effort to reduce road wear and improve air quality. I don't know of any sources in English off the top of my head though.

The last time I read an article about it though (2+ years ago, during Diesel-gate), the findings was that the danger in the particles comes from their size with smaller particles being more dangerous for humans. And that road particles were something like an order of magnitude larger than exhaust fume particles from diesel engines.

We've since banned diesel engines inside Stockholm as well so the whole thing is moot here.

>They're torn up from the road and rubbed off from the tyres themselves. The majority is obviously coming from the road.

Not sure even that adds up to believable.

The Sydney Harbour Bridge is about 500m long between the pylons. It has "more than 150,000 cars per day" on it (according to the snippet from a google search). If all of that was from the road, that'd mean there's about 160 tons of road getting torn up per year. It looks to be ~30m wide on Google Sat view, and "google first hit" research indicates road base weighs 1.9tons per cubic meter. It's be losing almost 6cm of depth along the whole span every year if all those numbers hold, or 3cm per year if "only half" of that comes from the road and the rest from the tires. They don't resurface it anything like often enough for that to be true...

Let's test it with basic math! The claim is "...performed some initial tyre wear testing. Using a popular family hatchback running on brand new, correctly inflated tyres, we found that the car emitted 5.8 grams per kilometer of particles.

If the average tire lasts 40,000 Kilometers then multiply that by 5.8 grams = 232Kg. 232Kg/4 tire per car = 58Kg per tire of tread. The tread is about 35% of the tire so the tire would need to weigh 165Kg. The average tire weights 20-22Kg, so that's a damn big tire!

New Asphalt might get tour up and account for additional particulate matter, but my understanding is that process slows considerably once the aggregate (small rocks) is exposed.

Perhaps it’s mostly existing particles laying on the road that are thrown up by the next vehicle’s tyres as it passes?

That's a pretty long stretch from the claim: "we found that the car emitted 5.8 grams per kilometer of particles".

But is it a long stretch from the claim: "Non-exhaust emissions (NEE) are particles released into the air from brake wear, tyre wear, road surface wear and resuspension of road dust during on-road vehicle usage."

Resuspension of road dust is literally one of the 4 things they defined as the NEE they're measuring.

OK, I missed that bit.

But counting "resuspended road dust" as "emissions" seems pretty far fetched to me. Especially if that's a significant portion of the "5.8 grams per kilometer of particles", and you then push out a press release with the hyperbolic headline claim "Pollution from tire wear 1000 times worse than exhaust emissions."

And they then have the audacity to claim: "Emissions Analytics seeks to bring transparency to a confused market sector."

Pretty sure I know who's funding them now, without even bothering to google it...

Who's funding them? Radical balloonists? Big Rail? Maybe it's the Hovercraft Lobby! I never did trust them.

Fossil fuel industry.

(But if it _is_ the Hovercraft Lobby, I'm totally in!)

It might be due to different tires. People in Sydney are very unlikely to be driving tires designed for ice and snow.

That doesn't make sense to me either. Take a busy German highway (as I don't know the average load on US ones), easily 100k cars per day. There are parts of highways which don't get replaced for 20 years easily. Plus apart from tiny fraction of north europe (and maybe Canada?), nobody ever uses studs.

Back of the envelope math tells me 1 km of highway would lose some 730 tonnes of asphalt, per year (so 14,600 tonnes in 20 years). If we talk about normal car wear, this simply isn't happening on those unkempt roads. It would leave huge lanes of deeper surface where asphalt is lacking. There isn't visible wear on lanes that are used mostly by cars like that. Roads have mostly potholes.

What happens on those roads is, sticky asphalt is worn away (but not at the mentioned rate), and what remains are stones which basically don't wear, and tires touch only that. At least highway surface I saw was like that.

What damages roads greatly are trucks, especially overloaded ones (say limit is 15 tonnes, they take 22 tonnes and hope to not be checked... welcome to east european mentality).

Indeed, trucks greatly damage roads. For example a 2 tonnes car has 2 axles, hence a=1 tonne per axle. A 20 tonnes truck with 2 axles has b=10 tonnes per axle. Then, the road damage per axle increases by a power of four [1], i.e., by (b/a)^4=10000.

[1] https://de.wikipedia.org/wiki/Vierte-Potenz-Gesetz

A rough way to think about road wear is the weight over one axle to the fourth power times the number of axles.

That gives you a quantity of force^4. How does that translate to road wear?

Empirical studies apparently find road wear matches a power law. Although it seems the exponent varies.

Here's a survey https://www.nzta.govt.nz/assets/resources/603/RR-603-The-rel...

That's for rutting damage, which doesn't necessarily translate linearly to particulate formation/flaking.

People use studded tires the US, too.

And Eastern Europe, colder parts of Russia etc.

> "the danger in the particles comes from their size with smaller particles being more dangerous for humans. And that road particles were something like an order of magnitude larger than exhaust fume particles from diesel engines."

Exactly. It might look bad when you compare the mass of particles, but if you compare the particle counts, it's exhaust emissions that produce the big numbers - of really tiny (sub-PM2.5) particles.

The studs in tyres are small carbide rods, which will easily chew through a soft material like asphalt. A rubber tyre would seem to be quite a bit softer than asphalt in colder conditions, so I have a hard time imagining the rubber wearing the asphalt down so significantly.

Study mentions EU and source company has offices in Stokenchurch, UK and Stuttgart, Germany. I doubt they tested with studded tires and called it typical.

They did test with brand new tires - that's the likely source.

"Emissions Analytics .. [self proclaimed?] leading independent .. specialist for .. measurement of realworld emissions .. performed .. initial tyre wear testing. .. on brand new, correctly inflated tyres .. [and] found that the car emitted 5.8 grams per kilometer of particles."

I don't think you can call it a study. They say they performed, "initial testing".

BANG - thank you.

Brand new tires have a molding protectant layer on them. "Scrubbing" is common in auto racing, on a new set.

I have been wearing studded slip on crampons when walking my dog this winter. The ice has been ridiculous, I’ve fallen twice already when not wearing them. Not great for the sidewalks, I know, but the dog needs his walks or he would... get sad

I cannot believe a studded shoe would have any impact whatsoever on a concrete pavement. Human weight is nothing compared to that of a car.

Weight of a masonry hammer is nothing compared to the weight of a human, yet it can destroy concrete with ease.

I'd guess it depends on how and how much you walk on what kind of pavement with what kind of studded shoes. Damage can realistically be imperceptible or ugly.

There are a lot more cars, running on much greater speed, for a lot longer distance, with much greater weight, then humans walking on spiked shoes.

The masonry hammer runs on much greater speed, with much more force, a lot more often then the human steps on the peace of concrete being taken apart.

Concrete sidewalks are pretty fragile. Unless they're freshly laid, most that I see have cracks and pits to some extent (probably mostly attributable to cooling/heating and water). Some people also seriously drop their feet down hard when they walk, and if they've got little bits of metal sticking out from the bottom of their shoes, I imagine that damage adds up and doubly so if it slams down an existing crack.

The ground pressure of a human wearing studded shoes is an order of magnitude or more higher than the ground pressure of a car.

The ground pressure of a car is exactly equal to the PSI that you inflate the tire.

Take the weight of a human and divide by the surface area of of a started shoe you will find a significantly higher number.

>>The ground pressure of a car is exactly equal to the PSI that you inflate the tire

Wait, what? So if the tire is flat, the car exerts no pressure on the ground? :-P

I know you are joking but just to answer the question anyway, if the tires are completely flat then they are not supporting the car and you can't use them for measurement.

If the tires are partially flat then they are supporting the car and the PSI is correct and you'll notice the tire spreads out wider on the road so the ground force is lower because it's spread out over a larger area.

Technically you have to also include the springiness of the sidewall in the measurement not just the PSI of the air.

>>if the tires are completely flat then they are not supporting the car and you can't use them for measurement.

Run-flat tires are a thing though - you can drive on them even with no internal pressure, there can be a gaping hole in it and you can still drive on them. So what's the pressure the car exerts on the road when driving then?

A hint: the area of the tyre in contact with the road is in square meters, and the mass is in kilograms.

You'll find that, if you multiply the force of gravity by the mass, and divide by square meters, you'll have Pascals.

And there's your answer.

That's where the "springiness of the sidewall" I mentioned comes in.

Normally (with inflated tires) it doesn't play much part. But with flat tires it can come to dominate.

I've done that. They catch fire, after a while.

I can understand the car part (pounds per square inch) but why would a person's feet have more than 35 psi? If I have something like 60 (30 per) square inches of feet, and I weigh 180lbs, would that be 3 psi for my feet? Even if only parts of my feet were striking the ground at a time, how would that be more than a car?

High heels. Also in this specific case we are talking about metal spiked ice shoes.

Thanks, that makes it very clear.

All your posts are helpful.

For example, I never before considered the implications of tire PSI.

By your logic, water running across concrete wouldn't create any wear on the concrete, but in truth, it does.

Yeah, but there's a lot of water, and it can run over concrete for hours if not days at a time - of course it has an impact simply due to the sheer volume of it. Again, how does it compare to the miniscule impact of studded shoes?

We have not banned diesel engines in Stockholm at all?

If the particles were coming from the road then roads would wear in very visible ways.

But we don't actually see that kind of wear. Roads don't typically have grooves on them where the cars go that are lower than the middle which doesn't have tires driving over it.

Come to Sweden sometime.

I've driven down highways where you don't have to steer because the ruts are so deep.

If you look it's actually p clear where on a road (e.g. highway) cars are driving , wear patterns can definitely be seen.

Some discussion down-thread about this also, somebody runs the numbers for the road itself.

If the emissions numbers are right, it can't be matter that is being consumed or discarded, so it has to be matter that is being returned to the system and "emitted" again. Crap on the road itself meets this requirement -- a car drives by, throws up a bit of rubber off the tires, a bit of asphalt off the road, and a lot of junk from the road surface, and almost all of this stuff falls back on to the road to be thrown up again by the next car.

The article doesn't say how the measurements were done, so it's possible they sampled a small fraction of the air and measured the density, so having the junk available to the sensor doesn't necessarily rule out the recirculation idea.

But if the junk is mostly recirculating, then maybe the health threat is not as bad as if it's being emitted off the road and being lofted into the air with a long dwell-time?

Lots of things are possible and consistent with what the article states, evidently more research is needed.

Rubber has a density of 1500 kg/m^3, a tyre wears about 5mm before it needs to be replaced. If I say a tyre has a radius of about 0.3 metres and a width of about 0.2 metres and plug this into the equation for an annular cylinder I get about 2kg of material lost between new and needs to be replaced per tyre. I don't know how long tyres last for most people, but I would guess about 50000km. So I would expect about 0.2 grams per km from tyres...

I did the calculation in Freedom Units and converted to grams per km. Assuming tires last 60,000 miles or 100,000km and got 0.1 gm/km. So matches your analysis closely.

Notable I put 60,000 miles on my cars tires since I bought it. They are due for replacement kind of whenever.

I hadn’t heard the term Freedom Units before, seemed obvious what you meant, looked it up anyway.

Universal measurements of American awesomeness. It encompasses all types of units (temperature, length, area, volume, speed, weight, GDP, etc).

https://www.urbandictionary.com/define.php?term=freedom%20un...

Excellent use of back of the envelope math. I wonder if maybe the loss is non-linear, and a bit more is coming off because the tires are brand new. Perhaps there’s some coating on new tires before they ‘break in’?

Perhaps, but that would have to be a pretty steep curve, and one would expect that kind of falloff to have shown up in the data here (unless they literally drove the car once for only 1km, which...would be its own problem for credibility).

Not if everyone only reads the headline!

"Non-exhaust emissions (NEE) are particles released into the air from brake wear, tyre wear, road surface wear and resuspension of road dust during on-road vehicle usage."

Roads are filthy. Cody's Lab once did a video where he collected road dust from the side of a highway, and refined out all the precious metals from it. That's from one small section of highway, just imagine the scale of the pollution across the whole of the states. Concrete dust, rubber, metals, fuel, oil. Cars and car infrastructure is dirty business.

https://www.youtube.com/watch?v=v5GPWJPLcHg

If one are outside near any mountainous road here in Northern California, motor vehicles pass by with the odor of brake pad + brake disc (mostly brake pad?) near the bottom with a very strong, distinctive bitter sweet metallic odor and that's probably a tiny proportion of the material.

Not sure if this test was set up to measure this, but brake dust, which contains all sorts of noxious particles, is a huge component of automobile emissions. This probably doesn't answer your question, however, because brake pads themselves only weigh so much...

I thought brake pads use asbestos which contribute to the noxious particles.

I do think Vehicle-to-vehicle communications will eventually minimize the all the chicken necking, evening out the traffic and thus less breaking.

Brake pads have not used asbestos in several decades.

New pads on new passenger vehicles haven't, but it's still legal to use asbestos in aftermarket pads.

https://parts.olathetoyota.com/what-are-brake-pads-made-of

Fitting or sale of automotive products containing asbestos has been banned in the EU since 2004

https://www.asbestosadvicehelpline.co.uk/is-asbestos-still-u...

I live in the other 75% of the world, though.

Unfortunately, I do not believe that this is true. My understanding is that it's still quite common, and even more so in developing countries.

Electric vehicles have regenerative braking when not braking hard. This dramatically reduces brake wear.

Hybrids as well.

A study linked last time this came up on HN indicated most of the particulate pollution is "resuspension", or previously generated particles kicked up by the car passing. It makes sense to consider in some cases but I think it's misleading to quote those numbers in some contexts, leading to confusion like this.

I would guess the measurement is more like how much dirt and dust is involved with a car driving driving down the road. Like brake dust, tire stuff.. and then that stuff being kicked up from the road surface by other cars and so on.

And yes it's super filthy and gross. I live on a busy street (but not a main street, so not THAT busy)... and my bathroom windowsills turn black after about a month because of brake dust and other car grossness.

Could there be an alternate way to measure the rubber wear off from vehicles? By considering the average distance after which a particular Sedan/SUV/Hatchback needs to change tyre, and then comparing the lost weights of old tyres and averaging that?

I'm just wondering if there are any alternate ways to correctly measure this emission.

Hypothesis: New tires have some break-in where they wear more than after the break-in period. To test- how much do 1 yr old tires emit?

Most of it must come from the asphalt.

I agree. But tires do shed a lot. Consider a brand new tire has grove depth of about 8-10mm, and many drivers change tires when their groves are 0-2mm (yes, some idiots keep driving until they have slicks or "a pop").

Turns out you don’t need to measure air pollutants, you can just divide lost rubber by the distance travelled. It won’t be anywhere close to what was measured, but then again actual particles are a much more useful number because you can’t breathe a worn down groove.

Then budget tyres surely wouldn't make a difference?

Yep, I was going to say. I believe new tires may initially shed far material, the same way that they offgas for weeks.

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