2019 rezulteo test: safety of worn tyres
Michelin invited us to Vienna to test its commitment for tyres offering long lasting performance right up to the legal wear limit. While regulations on this subject are about to change, the French tyre manufacturer took the opportunity to praise the action of authorities to guarantee wet safety with worn tyres.
A new regulation in preparation
“Wear can reduce the overall performance of a tyre by 20 to 50%”, claims Pierre Robert, Research and Development Director for the Michelin Group. This is an alarming fact for drivers looking for a safe ride. The problem is that today, there is no way of knowing how a tyre will handle after 10,000, 30,000 or even 50,000 kilometres. “All our studies show that there is no correlation between the performances of new tyres and those of worn tyres”, continued Pierre Robert. “A good tyre when new is not necessarily when worn”. This is why Michelin invited us to Vienna to present its objective and demonstrate the importance of testing tyres when they are new but also when they are worn.
At European institutions, a new general safety regulation is due to be adopted in autumn 2019. The principle of a mandatory test on worn tyres has already been introduced and more technical aspects are currently being discussed. An initiative welcomed by Michelin who supports the implementation of a minimum threshold for wet braking when tyres are worn. Motorists can then feel safe even when tyres are worn and not be tempted to change them before the legal wear limit. A good habit which would economise the production of up to 128 million tyres in Europe, due to tyres being changed too quickly, and save up to 6.6 million tonnes of CO2 emissions and up to 6.9 billion euros per year.
Wet braking test
To support its opinion, Michelin allowed us to drive in test conditions similar to those used to approve new tyres. The test was conducted at the ÖAMTC (Austrian Automotive, Motorcycle and Touring Club) at Teesdorf near Vienna.
A first braking workshop to decelerate from 80 to 20 km/h in wet conditions with 1 mm of water provided a quick check on performance differences. On one hand a Volkswagen Golf equipped with Michelin Pilot Sport 4 tyres worn down to 1.6 mm of tread, and on the other hand, the same car with entry level sports tyres, also at the legal tread limit. If Michelin’s comments are not intended to establish its superiority over competitors, the exercise demonstrated the significant difference in braking distances between two tyres, with a similar positioning, in the worn state.
If the car fitted with Michelin Pilot Sport 4 tyres took approximately 52 metres to decelerate to 20 km/h, the distance for competitor tyres was closer to 73 metres. Over and above pure grip, the road handling of the PS4 and its stability did not seem to be affected by wear. It is just the opposite for its counterpart which gave a real feeling of insecurity. It was subject to slight aquaplaning on the first metres, and then once the tyre was in contact with the track, the rear axle pulled and threatened to take the vehicle out of its trajectory. We finally came to a standstill off the wet track due to lack of space.
Wet track handling test
The second demonstration was conducted on a partially wet track, mainly in corners. Behind the wheel of an Audi A3, we discovered the differences in grip and handling at a standard cruising speed of around 50 km/h. A first car equipped with Michelin Pilot Sport 4 tyres worn down to 1.6 mm of tread proved to be safe and at no time were we in danger despite alternating between wet corners and dry sections of the track.
A second car equipped with the same entry level tyre as in the previous workshop, also with a tread depth of 1.6 mm, did not provide the same conditions. From the first wet corner, road handling became unbalanced causing excessive oversteering. With these tyres, the track became a skating rink even on the dry where we switched between over and understeering.
Although Michelin’s demonstration is a contest between two tyres which do not necessarily have the same price positioning, and by extension, performances which are behind their state when new, it has the merit of highlighting the current problem of worn tyres. With the future implementation of regulatory tests on worn tyres in wet conditions as well as a minimum threshold for performances, consumers would have a clearer idea of the performance of their tyres over time. This would also help reassure drivers about the safety of tyres throughout their service life.
Now it is up to authorities, and in particular the working group set up at the United Nations Economic Commission for Europe (UNECE), with participants coming from countries such as France, Italy, Spain, China and Japan to define the procedures for these new tests. By 2024 at the latest says Michelin.