Michelin : Changing Tyres At 3mm Unnecessary
By Kyle Lindsay
Thursday, May 18, 2017 - 12:30
Michelin is rejecting calls from parts of the tyre industry to increase the minimum legal tread depth from 1.6mm to 3mm.
The manufacturer says there is no link between tread depths at 1.6mm and increasing accident rates. In addition, changing tyres at 3mm would cost the motorist money and increase carbon emissions – especially as a tyre becomes more fuel-efficient as it wears.
An Ernst & Young report commissioned by Michelin found that changing tyres at 3mm instead of 1.6mm would cost European Union drivers an extra E6.9 billion a year in unnecessary tyre purchases and additional fuel consumption.
Instead, Michelin is calling for a change to the tyre testing regime to reflect wet braking performance at 1.6mm.
The Truth about Worn Tyres
Tyres do not perform the same when new – and as a tyre wears, and the tread depth reduces, the difference in performance will change, and differences may be accentuated. This is because tyre performance is affected by many individual characteristics; casing design, materials used, rubber compounds, tread design, shape of grooves and sipes etc. Modern tyre technology makes it possible to provide high levels of performance and grip from new, and through all of the tyre’s life down to the legal tread wear limit.
With this in mind, changing tyres early (i.e. before they are fully worn) does not guarantee greater safety, and no current studies have established a direct link between accident levels and tyre tread depth. Suggesting that tyres need to be changed early (before the legal limit / tread wear indicator is reached) is akin to enforcing a form of planned obsolescence. A consumer would not throw away his shoes just because they need cleaning, or the tube of toothpaste which was half full, so why would he do this with tyres if he can be convinced that it is safe to do so? Premature removal reduces the useful life of the product and would increase the frequency at which tyres are replaced. Not only would consumers have to make unnecessary purchases, but this would also have an adverse impact on the environment.
Changing tyres too early would result in 128 million additional tyres being used a year in Europe – which would cause nine million tons of additional CO2 emissions every year. In addition to the environmental impact, replacing tyres before they are fully worn also represents a significant and unjustified increase in costs for consumers; Ernst and Young estimates an extra 6 billion euros in Europe alone.
All tyres are not born equal in terms of performance, and this is even truer when the tyres are worn; but how do consumers know that the tyres they have bought will maintain a high performance level throughout their lives? How do consumers ensure they do not change tyres too early? At present, tyre tests are carried out on new products, but there is no consideration given to how their levels of performance will change over time. Michelin is now raising this issue – the fact that the only factor for safety is tyre performance – NOT tread depth. ‘The truth about worn tyres’ is calling on industry test bodies and consumer organisations to start comparing and testing tyres when they are worn to the legal limit.
The Truth about Worn Tyres – DRY BRAKING
When consumers reflect on road safety, they generally think about emergency braking in wet conditions – and with reason as braking distances increase in wet conditions. However, throughout Europe the road conditions are predominantly dry. In London, roads are dry for 71 per cent of days per year (106.5 days)* and with half the number of rainy days, the South of France has dry roads 85% of the time! Therefore, dry braking performance is important as these are the most prevalent conditions for all the vehicles throughout Europe.
The good news for motorists is that as long as tyres are not damaged in any way, the safety on dry roads actually improves as their tyres get worn. As seen on race circuits around the world, in dry conditions the ‘slick’ is the tyre of choice; and similarly for the ordinary motorist, levels of grip in dry conditions increase as the tyre tread depth reduces. A worn tyre will stop a vehicle more quickly in the dry than the same tyre when new.
Although the differences in stopping distance are not huge, demonstrations on the test track at Ladoux show a definite improvement, a shorter stopping distance on worn tyres in the dry.
Another surprising improvement in performance of a worn tyre over a new one is fuel consumption. As tyre tread depth reduces, the fuel economy of the vehicle will improve, and with one tank of fuel in five being used to simply overcome the rolling resistance of the vehicles tyres, this is a welcome benefit. The rolling resistance of a tyre at the point of removal at the legal tread limit is 80 per cent of that tyre in a new state. Therefore, keeping a tyre on the vehicle until the legal tread wear limit increases the time when it is in its most fuel efficient state, and reduces the motorist’s fuel bill.
Since tyre labelling, the awareness of tyre noise levels has increased – particularly in urban environments, and another benefit of worn tyres is that the noise level reduces as the tyre usage increases.
Michelin believes that consumers should think carefully before changing tyres earlier than the legal tread limit as they will be removing the tyre when the dry braking performance and fuel efficiency will be at their peak.
*UK Met Office data over a 30 year period shows 106.5 days of rainfall per year on average. Marseille has 53 days of rainfall per year on average. (Day of rain is 1mm of rain or above).
The Truth about Worn Tyres – WET LATERAL GRIP
When demonstrating tyre performance, comparing different tyre brands and different stages of a tyre’s life, it appears that the majority of testing is basic straight-line braking. Why do we not see more lateral grip demonstrations?
The simple reason for this is that it is relatively easy to measure, replicate and to quantify performance from wet braking tests, whereas the measuring of lateral grip and stability is very subjective and difficult to quantify. The good news is that wet lateral stability and wet braking are correlated. It is the same quality that is being tested, only the direction of the tyre travel that changes – one sideways/ laterally, the other in the direction of travel/ longitudinally.
Demonstrations at Ladoux confirm that a better tyre in wet braking, is also a better tyre in wet cornering.
The Truth about Worn Tyres – WET BRAKING
Michelin tests at Ladoux have shown that on wet roads, some worn tyres can perform as well as some new tyres, and that although the remaining tread depth is a factor in wet braking, the performance of the tyre, at all stages of its life, is more important.
Tyre performance is affected by many factors; casing design, materials, rubber compounds, tread design, shape of grooves and sipes etc. and these all affect how the tyre performs throughout the tyre’s life – right down to the legal tread wear limit. All tyres do not perform the same when new – and the differences in performance are more accentuated when that tyre is worn, according to their design.
Tyre labelling and European regulations have brought in minimum standards for tyre performance, and particularly for wet braking – one of the criteria measured by tyre labelling. Whilst all tyres legally sold in Europe meet this minimum standard when new, Michelin tests have shown that the wet braking capabilities of some tyres reduce quickly when worn, and may fall below this ‘minimum standard’ requirement. However, some premium products not only meet the criteria when new, they do so when worn to the legal tread wear limit.
Michelin workshops at Ladoux have shown that a premium tyre, worn to the tread wear limit can perform as well as a brand new lower performing tyre.
With these findings that wet braking distances and lateral wet grip depend on the performance of a tyre and not solely the tread depth, Michelin is calling on industry test bodies, and consumer organisations to start comparing and testing tyres when they are worn to the legal limit; then consumers will start to discover the truth about worn tyres.