2. 47th PMP IWG Meeting – Ispra (IT) – 17.05.2018
EXPERIMENTAL INVESTIGATION OF TREAD WEAR AND PARTICLE EMISSION FROM TYRES WITH DIFFERENT TREADWEAR MARKING
Theodoros Grigoratos1, Mats Gustafson2, Olle Eriksson2, Giorgio Martini1
1 European Commission, Joint Research Center, Sustainable Transport Unit
2 Swedish National Road and Transport Research Institute (VTI), SE Linköping, Sweden
47th PMP IWG Meeting – Ispra (IT) –

3. Outlook Background Scope of the exercise Methodology
Results & Discussion
Wrap up

4. BACKGROUND
June 2013: The PMP IWG started looking into non-exhaust traffic related particle emissions
i. Why did the PMP IWG get involved into this research?
There was a request from the Russian federation towards the UN GRPE group to investigate tyre wear emissions
DG-GROW (DG responsible for emissions legislation in the EC) requested to extend the research also to other non- exhaust traffic related sources (i.e. brakes, clutch, resuspension)
March 2014: Publication of a JRC Science and Policy Report (JRC-89231)* which summarized the situation regarding non-exhaust particle emissions *

5. BACKGROUND
January 2015: The PMP group separated tyres and brakes research
June 2016: The UN GRPE approved the new ToR which for tyres foresee the continuation of monitoring on-going projects and published data
ii. Why did the PMP IWG follow a different approach for tyres and brakes?
The issue of tyres’ emissions proved to be more complicated compared to brakes. Many fundamental questions were not (and yet have not been) answered
Different views from the tyre industry compared to already published data (small contribution to air pollution, no significant risk for human health, nature of abrasion particles, etc.). PMP agreed to keep under review and revisit and develop an action plan before the end of the 3 year mandate period

6. SCOPE OF THE EXERCISE
The aim is to explore the relevance of expected tyre durability expressed as the Treadwear Rating (TWR) for total tyre wear as well as for PM and PN emissions from the interaction between the tyre and the road surface.
iii. What is the Treadwear Rating (TWR)?
The Treadwear Rating (TWR) provided by tyre manufacturers on the sidewall of summer tyres is a marking intended to inform the customer about the expected durability of the tyre (USA – “49 CFR Uniform tyre quality grading standards”)
TWR uses numbers from 100 to about 700. The higher the number, the higher the mileage that the customer can expect to drive before reaching the minimum allowed tread depth

7. SCOPE OF THE EXERCISE
v. Why was this approach decided?
The investigation of all open issues would require a full-scale project which was not possible with the limited resources available within the PMP group
JRC decided that it would be faster and easier to explore whether the number and size of tyre wear particles correlate with their mass as well as with the mass loss of the tyre over its lifespan
If this hypothesis would have been confirmed particle emissions from tyres could be controlled through the mass loss of the tyres during their lifespan and therefore through the Treadwear Rating value

8. METHODOLOGY
The road simulator consists of four wheels that run along a circular track with a diameter of 5.3 m
The wheel axles have different lengths thus positioning the wheels in different distances from the centre
Any type of pavement can be applied to the simulator track
Pavement made of 14 asphalt pavements of stone mastic asphalt with different max aggregate sizes

9. METHODOLOGY
Number
Tyre (205/55 R16)
TW Rating (TWR) 1 A0
180 2 B1
300 3 C1 4 D1 5 B2
400
Five summer tyres (205/55 R16) were chosen to study variation in wear and particle emission
Tests were performed under normal environmental conditions (20°C) over a constant speed of 70 km/h
A total of 210 km was run for the purpose of investigating total wear of the tyres (weighting)
PM10, PM2.5 (TEOM, DustTrak) and PN (APS, SMPS) studies were conducted over 3 days based on a statistical optimal sequence

10. TYRE TREAD MASS LOSS – COMPARISON WITHIN THE SAME BRAND
RESULTS AND DISCUSSION
TYRE TREAD MASS LOSS – COMPARISON WITHIN THE SAME BRAND
There is a substantial (not statistical significant) difference in the mass loss between the two tyres of the same brand (B)
The tyre with the lower TWR (A0) showed lower mass loss compared to 300 TWR tyres

11. RESULTS AND DISCUSSION
TYRE TREAD MASS LOSS – COMPARISON OF TYRES OF THE SAME TWR
There is a substantial (not statistical significant) difference in the mass loss between the tyres of the same TWR (300)
B1 tyre showed much higher mass loss compared to the other tyres of 300 TWR
No prediction of the mass loss can be done based on the TWR
Tyre Number
Tyre
TWR
Mean mass loss per tyre (g)
Loss per km and car (mg) 1 A0
180
2.9 55 2 B1
300
11.3
214 3 C1
3.2 61 4 D1
4.6 87 5 B2
400

12. RESULTS AND DISCUSSION
PM10 CONCENTRATION
The PM10 quasi-stable levels reached for different tyres are close to 20–30 µg/m3 (DustTrak) and 40–50 µg/m3 (TEOM)
B1 tyres seem to reach a slightly higher quasi-stable PM10 level compared to B2
A0 (TWR=180) tyre seems to have low PM10 emissions and in any case not significantly higher than the rest of the tyres

13. RESULTS AND DISCUSSION
PM2.5 CONCENTRATION
The PM2.5 levels reached for different tyres are close to 10–15 µg/m3 (DustTrak)
Approximately 50% of the emitted particles (by mass) fall within the size range of PM2.5 (measured DustTrak – calculated APS)
Due to the relatively low level of the PM2.5 it is difficult to reach a conclusion regarding the effect of TWR on PM2.5

14. RESULTS AND DISCUSSION
PN CONCENTRATION
PN concentrations were generally low and revealed a complex pattern from day to day (Figure shows Days 1 and 3, respectively)
No particular conclusions can be drawn regarding the effect of TWR to PN concentrations

15. MASS SIZE DISTRIBUTION
RESULTS AND DISCUSSION
MASS SIZE DISTRIBUTION
Bimodal mass size distribution (not very distinct) was observed
There is a very wide peak at the coarser size range (4-7 μm) confirmed over all days and another at approximately 1 μm
TWR does not seem to have any effect on the mass size distribution of the different tyres

16. NUMBER SIZE DISTRIBUTION
RESULTS AND DISCUSSION
NUMBER SIZE DISTRIBUTION
Very low particle number concentrations in most of the cases
Unimodal PN distributions with the peak being at the Ultrafine particle size (20-30 nm)
TWR does not seem to have any effect on the number size distribution of the different tyres

17. WRAP-UP
There is no general relation between TWR and measured tread mass loss or PM10, PM2.5 or PN concentration
Tyres of different brands and same TWR display different wear as well as PM10 and PM2.5 concentrations, thus not allowing a categorization based on the TWR
Within the subset of two B tyres the one with lower TWR has higher tread mass loss and PM10 emissions. Further research with more tyres of same brand and different TWR is required to confirm the feasibility of categorization within the same brand

18. WRAP-UP
Approximately 50% (by mass) of emitted PM10 fall within the size range of fine particles
Particle mass size distribution is bimodal with one peak falling to the coarse size range and another to the fine size range
Particle number size distribution is unimodal and is dominated by ultrafine particles most often peaking at 20–30 nm
The total tread mass loss was found to be 3-11 g/tyre resulting in a calculated wear rate of mass loss between 55–212 mg/km per vehicle*
*This does not refer to PM emissions factors BUT total mass loss of the 4 tyres

19. Any questions?
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20. NEXT STEPS
June 2016: According to the ToR the PMP IWG should provide GRPE with a report for consideration in Jan 2019 on the investigation status (on-going projects) and recommended next steps
vi. What is the current status concerning tyre wear particle emissions?
There have not been substantial changes with respect to the situation back in There are still fundamental questions which have not been answered
A full-scale investigation of all open aspects related to tyre wear emissions would not be compatible with the limited resources available within the PMP IWG
Not many groups worldwide are currently dealing with this issue and most of the information come from the TIP Project

21. NEXT STEPS
vii. Which could be the next step to tackle tyre wear particle emissions?
A possible solution could be the development of a definition for tyre abrasion (wear rate) and of a commonly accepted methodology to measure it
The knowledge of the tyres’ abrasion would allow to rate different tyres on the basis of material released into the environment. Need to confirm the relationship between the amount of the released material and the impact on air quality
The knowledge of the abrasion rate of the tyres might be useful also for other parameters such as microplastic emissions, durability of the tyres, etc.
The development of such methodology has been mandated at the EU COM level in the IA accompanying the proposal for the regulation on labelling of tyres expected to be approved

22. NEXT STEPS