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New Michelin tyres last longer, and save fuel without sacrificing grip

What do you think about car tyres?

 

Research suggests not very much, until you need a new set.

 

If I rack my brains I think life, economy, grip, comfort, noise, feel, puncture resistance, price. Add low temperature performance and no tyre can offer all nine. You need a different tyre for snow and ice than you do for summer.

 

But I only come up with nine attributes because I spend half my life answering questions about cars. When people are properly researched, the main factors they think about tyres are economy, safety and longevity.

 

And this is no idle research. It’s straightforward questions the answers to which are verified by a sophisticated cross-questioning “trade off “ technique that makes sure the respondents are revealing what they really think rather than what they think the researcher wants to hear.

 

Longevity remains Michelin’s prime attribute, usually meaning that the company’s slightly more expensive tyres cost less in the long run. Relatively low rolling resistance means they also save you money in fuel. But no driver puts longevity and fuel saving over safety, so Michelin’s tyres must also provide grip at least the equivalent of the competition.

 

And that is what Michelin set out to prove to us at the ADAC testing facility near Berlin.

 

Michelin tyres are tested not by Michelin itself, but wholly independently by DEKRA, based in Narbonne, South West France and by the respected German organisation TUV, that has been testing and certifying products generally for 140 years.

 

The tyres are all bought from different retail outlets in different European markets to prevent any ‘special’ tyres being supplied that could distort the results of the tests.

 

Economy

 

Tyres are responsible for 20% of a car’s fuel consumption (and 30% of a truck’s). Obviously all 20% cannot be eliminated by choice of tyre, but 5% can be. 5% of 50mpg is 2.5mpg. So worth saving.

 

Distortion and flexing increase tyre temperature and increase rolling resistance, so it is vital to run tyres at the correct temperature for the weight of the car and the load being carried. Tyre pressure can increase by 0.3 bar over the course of a morning, so that needs to be taken account of too. As must the compound of the tyre, a mix of carbon black and silica. But since both carbon black and silica are available in different compositions and the compositions of each affect each other differently, getting the right mix and mixing the mix in the optimum manner can make a huge difference to rolling resistance.

 

Rolling resistance that brings the direct benefit of fuel economy can be measured in a drum test by TUV, that conforms to ECE R1007 / SOO 28580 1srt edition 2009.

 

Tyres are rotated against a 3-metre drum driven by an electric motor. The braking effect, deceleration and the power drawn by the electric motor to turn the drum and the tyre are all measured.

 

In these tests of 175/65 R14s with Michelin Energy Saver as the 100% control tyre, the others scored down 81%.

 

Testing 225/40 R18s with the Michelin Pilot Sports as the 100% control tyres the others scored down to 88%.

 

And testing 205/55 R16 winter tyres with Michelin Alpin A4s the control tyre the others scored down to 89%.

 

We also took part in a physical test where three identical Golf diesels fitted with 225/40 R18 tyres were allowed to freewheel off a ramp alongside each other. The tyres were Michelin Pilot Sport 3, Continental Contisport Contact 3 and Bridgestone Potenza REO5A, all purchased by DEKRA in the marketplace rather than supplied by manufacturers. As we saw, the Golf on the Michelins rolled considerably further than the other two.

 

To verify the rolling resistance tests, three other Golfs were taken by DEKRA the same day on a 300 mile convoy run fitted with the same three tyres, rotated every 100km from car to car to eliminate any differences from different performances of the cars themselves.

 

At the end of the test, the Michelins had achieved 4.59 litres per 100km, the Continentals 4.7 litres per 100km and the Bridgestones 4.8 litres per 100km. Over 10,000 kilometres this is the equivalent of 686 litres for the Michelins, 706 litres for the Continentals and 720 litres for the Bridgestones. Over 10,000km (6,250 miles) that’s 34 litres, and at £1.20 a litre adds up to £40.80.

 

Longevity

 

To test longevity over 10,000 kilometres DEKRA has the cars driven in convoy by professional drivers who are rotated car by car to eliminate differences in their driving styles. The tyres themselves are swapped car to car in a daily basis, always going to the same corners of the cars to further eliminate external differences.

 

Testing 175/65 R14 Michelin Energy Saver on Peugeot 207s in this manner, and making the Michelin the control tyre at 100% showed a variation in longevity over 10,000 kilometres down to 66% of the Michelin result.

 

The same test pitting 225/40 R18 Michelin Pilot Sport on VW Golf 2.0 diesels showed a variation down to 71% of the Michelin result.

 

And the same test of 205/55 R16 Michelin Alpin A4 winter tyres on Audi A4 B8s showed a variation down to 51% of the Michelin result.

 

Safety

 

Front of mind with most tyre buyers is safety. How well a tyre grips.

 

The contact area of most tyres on the road at any one time while the car is moving is about the size of an adult hand. So not very big.

 

On a dry road, 75% of grip is achieved by adhesion, in other words the way the rubber tends to stick to the surface. The other 25% of grip is created by indentation, in other words the way the rubber distorts to match the road surface.

 

This itself is affected by the Macro roughness of the road surface (the size of the stones) and the Micro roughness of the road surface.

 

However, to grip on a wet surface, the tyre must evacuate the water between the tyre and the road so the tyre treads actually run on a dry surface. So tyres are designed like a boat to displace the water between the tread and the road. The sipes (or cuts) in the tread cut through the film of water. The grooves in the tyre take the water from the contact area and disperse it during the rotation of the tyre.

 

We physically pitted three tyres against each other in a wet braking test from 80kmh to 10kmh. They were Michelin Pilot Sport PS3, Bridgestone Potenza RE050A, and Continental Sportcontact 3, 225/40 R18. In this test, using eight different drivers, each driving the three different tyres, the Continentals actually won at an average of 26.5 metres stopping distance, the Michelins were an almost identical close second at an average 26.8 metres and the Bridgestones achieved an average 28.6 metres.

 

This was not quite reflected in TUV’s separate wet braking tests where, taking the wet braking performance of the Michelins at 100%, the Contis scored 95% and the Bridgestones 93%.

 

Yet in the TUV testing of 205/55 winter tyres, taking Michelin Alpin 4 as the control tyre at 100%, the Michelins were slightly outperformed by Conti Wintercontact TS830, at 101%; Dunlop SP Winter Sport 3D at 102% at 102% and Goodyear Ultragrip 7+ at 103%. So this was no whitewash for Michelin.

 

However when TUV tested the other characteristics of the tyres this showed that the Continentals and the Dunlops and in particular the Goodyears had sacrificed considerable longevity for slightly greater grip.

 

EC Directives

 

Soon every tyre will have to carry a sticker showing its rolling resistance (A to G, missing out D as the control 100%), wet braking (A to F) and drive by noise in dB(A).

 

The EC is also legislating for overall tyre performance in three areas: wet braking performance, rolling resistance, and tyre noise, and has laid down performance levels that all car tyres must meet from November 2012. Some of the detail of the testing methods and their calibration still needs to be confirmed and there will be no testing for longevity due to the cost and time required to test each and every tyre for longevity.

 

You can’t have absolute peak performance in every characterising in any tyre. But Michelin has demonstrated that for ordinary high profile tyres, for low profile performance tyres and even for winter tyres you can combine safety, fuel economy and longevity in the same tyre.

 

 

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