Michelin sets record straight over tyre wear…

There’s a big debate on in Europe at the moment about possible law changes around minimum tyre tread depths.

Some believe a minimum tread depth of 3mm, instead of 1.6mm, will improve safety.

And while this would undoubtedly drastically increase tyre sales, Michelin isn’t supporting the calls for the change.

The tyre manufacturer says changing tyres before they’re fully worn is nothing more than a waste of money…

The Truth about Worn Tyres (according to Michelin)

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.

Changing tyres early does not guarantee greater safety.

Dry Braking Performance

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.

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% 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.

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.

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.

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.

These findings show 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.