Worn tyres: The REAL facts about replacement – and when

  • Controversial findings from Michelin research
  • Is current tyre-testing outdated for all weathers?
  • Too-early tyre changes can affect performance, fuel use

LONDON, England – Michelin has rejected calls from sections of the tyre industry to increase the minimum legal tread depth from 1.6mm to 3mm. Find out why here…

Such a tread-depth increase would, of course, been nice for the tyre-making business because it would mean the law requesting vehicle owners to replace their rubber more frequently.

Michelin doesn’t see it that way, and here’s why…

The French tyremaker says there’s no link between tread depths at 1.6mm and more road incidents. “Changing tyres at 3mm,” a media release sent to Carman’s Corner said, “would cost vehicle owners money and increase carbon emissions – especially because a tyre becomes more fuel-efficient as it wears.”

CHANGE NEEDED FOR TYRE-TESTING

An Ernst & Young report commissioned by Michelin found that changing tyres at 3mm instead of 1.6mm would cost European Union drivers the equivalent of R117-billion a year in unnecessary tyre purchases and greater fuel-consumption.

Michelin would prefer a change to the tyre-testing regime to reflect wet-braking performance at 1.6mm.

And here’s what Michelin says is the truth about worn tyres…

TYRES DON’T perform the same when new: as they wear and the tread depth reduces the difference in performance will change – and differences may be accentuated – because tyre performance is affected by many individual characteristics:

  • Their casing design
  • Materials used
  • Rubber compounds
  • Tread design
  • Shape of grooves and sipes.

“Modern tyre technology,” Michelin explains, “makes it possible to provide a high level of performance and grip right through the tyre’s life down to the legal tread-wear limit.

“With this in mind, changing tyres (efore they are fully worn) does not guarantee greater safety; no current study have established a direct link between accident numbers and depth of tyre tread.

“Suggesting that tyres need to be changed 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 a half-used tube of toothpaste, so why do so with tyres if it is safe to continue using them?”

R89bn BONUS FOR TYRE MANUFACTURERS

Premature removal, the statement adds, will reduce the useful life of the product and increase the frequency of replacement. “People would not only have to make unnecessary purchases but also adversely affect the environment.”

Such a legal decision would, Michelin research showed, would add 128-million tyres to the dump each year and generate nine-million tons of CO2 emissions every year. Not mention an extra R89-billion in Europe going to the tyre companies, according to Ernst and Young.

Tyre are not made equal in terms of performance, Michelin says. “This is even more true when the tyres are worn; but how do people know the tyres they have bought will maintain a high level of performance throughout their life?

How do people make sure they don’t change tyres too soon? Tests are done on new products but no consideration is given to how their performance will change over time. Michelin says the ONLY factor for safety is tyre performance – NOT tread depth.

The Truth About Worn Tyres’ wants industry test bodies and buyers’ organisations to compare and test tyres when they are worn to the legal limit.

The Truth About Worn Tyres – DRY BRAKING

PEOPLE reflectIng on road safety usually think about emergency braking on a wet road – indeed, such braking does take longer in both time and distance. Michelin again: “However, throughout Europe, roads are predominantly dry. In London they are dry for 71% of days a year (106.5 days)*.

“The south of France, with half the number of wet days, has dry roads 85% of the time so dry-braking performance is important as ‘dry’ is the prevalent condition for all vehicles throughout Europe.

QUICKER WET STOPS POSSIBLE ON WORN TYRES

Safety on dry roads, Michelin says, improves as tyres wear because more rubber in touchng the tar. Worn tyres, on a dry road, will stop a vehicle more quickly than the equivalent new. Although the differences in stopping distance are  not huge, demonstrations on the Michelin test track at Ladoux produce shorter stopping distances on worn tyres in the dry.

Another surprising improvement in performance of a worn tyre is fuel consumption. As tread depth decreases so fuel consumption drops. As much as one tank of fuel is in five is used to overcome the tyres’ rolling resistance.

The rolling resistance of a tyre at the current legal tread limit is 80% that of a new one so keeping a tyre on the vehicle until the legal wear limit increases the time when it is at its most fuel-efficient.

Worn tyres are also quieter – a benefit for cities.

So, Michelin believes people should think carefully if they are changing tyres before it is necessary.

*UK Met Office data over a 30 year period shows 106.5 days of rainfall per year on average. Marseille has 53 days of rain per year on average. (Day of rain = 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 seems most testing is basic straight-line braking. Why not more lateral (sideways) grip demonstrations?

The reason, Michelin says, is that it’s relatively easy to measure, replicate and quantify performance from wet-braking tests; measuring lateral grip and stability, however, is very subjective. The good news is that wet lateral stability and wet braking are correlated. It’s the same quality being tested, only the direction of tyre travel 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 some worn tyres can perform as well in rain as some new tyres and that though 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 each affects how the tyre performs throughout its life. All tyres don’t perform the same when new – and the differences in performance are more accentuated when that tyre is worn.

PREMIUM TYRES GOOD TO THE LIMIT

Tyre labelling and European regulations have brought in minimum standards for tyre performance, particularly for wet braking – a criteria measured by tyre-labelling. All tyres legally sold in Europe meet this minimum standard when new but Michelin has shown the wet-braking ability of some tyres reduces quickly when worn and may fall below this ‘minimum standard’.

However, some premium products not only meet the criteria when new but also when worn to the legal limit.

Michelin workshops at Ladoux have shown that a premium tyre worn to the tread-wear limit can perform as well as a new less-competent 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.

That way people will start to discover the truth about worn tyres.

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