Michelin Makes case for Not Changing Tires at 3 mm

Michelin has declared that it sees little need to increase the minimum legal tread depth from 1.6mm to 3mm. The manufacturer has found no correlation between increase in accidents and tread depths at 1.6 mm. The company feels that increasing the minimum legal tire tread depth would only lead to greater harm to the environment with the negative outcomes being increasing carbon emissions and greater costs to the motorist. This is particularly relevant in view of the fact that tires generally become more fuel efficient as they are used for a longer time.

An Ernst & Young report commissioned by Michelin found that changing the minimum tread depth to 3 mm instead of 1.6 mm would cost motorists in the European Union an extra 6.9 billion euros on an annual basis in unnecessary tire purchases and additional fuel consumption. Instead, Michelin feels that it would be better to implement a new tire testing regime that would compare and reflect the wet braking performance of different tires at 1.6mm.

As a tire wears, and the tread depth reduces, the difference in performance will change, and differences may be accentuated. Tire performance is affected by many individual characteristics; casing design, materials used, rubber compounds, tread design, shape of grooves and sipes etc.It is pointless to change tires before they are fully worn as that will not increase safety. There are no current studies directly linking accident levels and tire tread depth. Replacement of tires before it is needed reduces the lifespan of the tire, increases the frequency of replacement, cost to the consumer and the adverse impact on the environment. All tires do not demonstrate the same level of performance, especially when they have worn a little. It is vital for customers to be aware of the performance of their tires as they wear out.

Currently, tire tests are carried out on new products, but no tests are required by law to assess how the performance of the tires varies as they age. Michelin is now trying to raise this issue and emphasizing the concept that the only factor that affects the safety of motorists, is the performance of the tires and NOT tread depth. The report ‘The truth about worn tires’ is calling on industry test bodies and consumer organizations to start comparing and testing tires when they are worn to the legal limit.

As long as tires are not damaged in any way, the safety on dry roads actually improves as their tires get worn. Even on racing circuits, in dry conditions the ‘slick’ is the tire of choice. For the ordinary motorist also, the grip of the tires increases in dry conditions as the tire tread depth reduces. It is easier to stop a vehicle in dry conditions if the tire is worn than if it is 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 tires in the dry.

When the fuel efficiency of a worn tire is compared to that of a new tire, the fuel consumption of a new tire is higher. As tire tread depth decreases, tires become more fuel efficient. Normally, 20 per cent of fuel is consumed to overcome the rolling resistance of the tires. Rolling resistance decreases as tires are used and at the legal tread limit is 80 per cent of the rolling resistance of a new tire. Hence, using tires till the legal tread wear limit increases the span during which the tire is in its most fuel efficient state, and lowers the overall amount spent on fuel.

Another factor to consider is tire noise levels, especially in urban environments. In the case of worn tires, the noise level decreases as the tire usage increases.

If tires are changed too early, 128 million additional tires would need to be used in Europe. Another adverse impact would be nine million tons of additional CO2 emissions every year. Ernst & Young estimates that consumers would be spending an extra 6 billion euros in Europe alone.

Michelin believes that consumers should think carefully before changing tires earlier than the legal tread limit as they will be removing the tire when the dry braking performance and fuel efficiency will be at their peak.

The Truth about Worn Tyres – WET LATERAL GRIP
Conventional tire tests compare different brands of tires and tires at different stages of usage, and there are very few tests of lateral grip. Most tests assess basic straight-line braking, as this is easy to measure and quantify during tests. Lateral grip and stability is very difficult to measure and quantify objectively. Wet lateral stability and wet braking are linked to each other. The Ladoux demonstrations proved that if a tire is better in wet braking, it is also a better tire in wet cornering. The only change with regard to the two parameters is the direction of the tire. In wet cornering, the tire travels sideways or laterally, while in wet braking, the tire is tested longitudinally or in the direction of travel.

The Truth about Worn Tires – WET BRAKING
Michelin conducted tests at Ladoux on wet roads, and these tests indicated that worn tires exhibited performance that is as good as that of some new tires. While the remaining tread depth is a factor in wet braking, it is the performance of the tire throughout its life cycle that is more important.All tires do not perform at the same level when they are new and as the tires are used more, these differences increase, based on their design.

Europe has minimum standards for tire performance, and especially for wet braking, which is used as one of the criteria for tire labelling. All tires sold in Europe meet the preset criteria when new, but when it comes to wet braking, different tires experience drop in their capabilities at different rates. Some quickly fall below the ‘minimum standard’ while some premium tires meet the wet braking requirements even when they are worn down to the legal tread wear limit. Michelin conducted tests at its workshops at Ladoux which proved that a premium tire, even when worn to the tread wear limit exhibits performance that is just as good as that of a lower performing tire that is brand new.

Based on Michelin’s findings, the leading tire manufacturer is now encouraging consumer organizations and industry test bodies to start comparing and testing tires when they are worn to the legal limit to verify whether they are still in a usable condition. Then, the truth about their condition will come to light.