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Michelin reveals all about worn tyres

Michelin reveals all about worn tyres

Chris Russon, 2017-05-15

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TALK of tyres can provoke hot debate and none more so than when it comes to road safety.

It's all a matter of grip and stopping distance, particularly in the wet.

Yet that has stirred up a hornet's nest with calls to increase the minimum legal tread depth by a significant margin.

Unnecessary, says Michelin claiming such a move will hit motorists in the pocket and damage the environment.

To debunk the myth that tread depth alone is critical, the tyre maker has just staged a demonstration at its Ladoux test track in France to show exactly how worn tyres perform.

Michelin says there is no direct link between accident levels and tread depth and has also flagged up a study by Ernst and Young which estimates that increasing minimum tread depth from the current 1.6mm to 3.0mm would cost motorists in Europe almost £5 billion.

According to Michelin, safety is all about general tyre performance, not just tread depth and the results from Ladoux were an eye opener.

Comparing budget-buy against mid-range tyres already worn to the legal minimum, the difference in stopping distance in the wet was astonishing.

Performing emergency braking from 60mph in a Volkswagen Golf the car took almost 60 metres to stop on budget tyres. On mid-range rubber it took 48 metres - a difference of some three car lengths.

On a skid pan circle - which replicates cornering performance - the fully worn mid-range tyres broke away at just under 40mph while on brand new budget tyres with a full set of tread the car started to skid at 35mph.

Straight line braking performance in the wet - this time using a Citroen C4 - also showed big differences between premium brand and budget-buy tyres.

Even in the dry, worn tyres can throw up some surprising statistics and deliver more stopping power than new ones.

From just over 60mph a Golf shod with new Michelin CrossClimate tyres came to rest in 37.5 metres, on worn rubber it stopped in 35.4 - think slick tyres on racing cars and it all falls into perspective.

Point taken then that better quality tyres out-perform cheaper alternatives at the limits and to back that up Michelin produced the results of tests it has carried out on 24 different sets of tyres showing the differences in stopping distances when new and worn.

"All tyres are not equal when they are new - and what our tests at Ladoux have shown us is that tyre performance is even less equal when worn," said Terry Gettys, Michelin's boss of research and development.

"In fact the differences are very much accentuated once a tyre is in the latter stages of its life. Quite surprisingly we have discovered that some tyres worn to the legal limit have a wet braking distance virtually the same as some new tyres."

That speaks volumes and the difference comes down to all round tyre construction and not simply the amount of tread. In fact, in all the tests we witnessed at Ladoux the cheaper tyres performed the worst.

The current regulations governing minimum tread depth were set out in the 1980s and motorists face a penalty of three points and a fine of up to £2,500 for each illegal tyre or even a potential ban.

On average a new tyre will come with some 7.0mm of tread and while no-one disputes that more tread makes for better all-round grip, Michelin is quick to point out that a tyre finds its ‘sweet spot' as it wears.

As the tread diminishes so does the rolling resistance which results in improved fuel economy and less road rumble - all characteristics flagged up on the EU Tyre Labels which have had to be fixed on new tyres since 2012.

With tyre performance accounting for some 20 per cent of a vehicle's fuel efficiency and the rolling resistance of a tyre with 1.6mm of tread being 80 per cent less than when new, increasing the legal limit of tread depth would also hit fuel consumption.

Michelin estimates that changing tyres earlier would result in 128 million additional tyres being used every year in Europe and that alone would increase continental CO2 emissions by a staggering 9,000,000 tons - that's the equivalent of 825,000 gallons of fuel, enough to drive an average car more than 1,000 times around the world.

"If tyres are changed early, before the legal limit, this reduces the useful life of the product, and consumers would make unnecessary purchases," said Mr Gettys. "This would also have an adverse impact on the environment.

"So, early tyre removal has a huge environmental impact and also represents a significant and unjustified increase in costs for consumers."

As well as keeping the legal requirements for tread depth at 1.6mm Michelin is now calling for changes to the labelling system to give motorists a bigger picture by showing how tyres perform when worn.

That, says Michelin, would reflect its workshops at Ladoux which show that a premium tyre, worn to the current tread limit can perform as well as some brand new budget tyres.

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