10/06/2004 High wear on summer tires in winter use

Hanover, October 2004. Winter tires are essential for safe driving during the cold weather. And they are good for the wallet, too. Anyone driving summer tires through the winter has to accept that his mileage performance will be up to 20% lower. This is revealed by a new study carried out by Continental, Europe's market leader for winter tires. The substantially higher wear is caused by the compound in summer tires freezing at temperatures below 7 degrees. The subsequent higher mechanical stress and material fatigue means a considerably lower mileage performance on summer tires driven through the winter. Motorists who switch to winter tires in good time not only invest in their own safety, but also lighten the load on their wallet.

The press release can be downloaded as doc-file here (39 KB).

Summer and winter tires are becoming increasingly specialised. In particular tires for more powerful, sporty cars need compounds which offer optimum grip, high-speed stability and mileage performance during the warmer weather. However, this type of compound has a drawback - at low temperatures it hardens and provides less grip, and it is precisely this grip which is desperately needed to effectively transmit those forces to the road that occur in dangerous situations.

One drawback with modern summer tires is their substantially reduced mileage performance in winter use: "A new study has revealed that there is substantially greater wear on summer tires driven at low temperatures" comments Dr. Holger Lange, winter tire developer at Continental. "The reason for this can be found in the conflicts of objectives which we have to resolve when developing summer tires." These conflicts of objectives occur particularly between driving performance in the wet and in snow, between characteristics in the wet and rolling resistance, as well as between driving characteristics on dry roads and on icy stretches. "The compound used on summer tires freezes up quickly at low temperatures" explains Dr. Lange. "As a result, the material hardens and loses elasticity." This means substantially higher wear - and thus lower mileage performance.

Describing the process Dr. Lange says: "Wear occurs when the chemical bonds in the tire tread dissolve. The forces occurring during driving lead to breakages in the polymer chains. The very great mechanical tensions cause the polymer chains to tear, and increased tire wear is the result."

The vehicle itself with its drive concept, weight and engine power also contributes significantly to tire wear. The greater the weight and engine power applied to the road, the greater the tire wear. "On a Citroën 2CV, for example, there is little wear" explains Dr. Lange. "With its 28 horsepower (20 kW) and a weight of 600 kg, the 2CV suffers little wear when driving. On the other hand, on a Mercedes E-Class with its 177 hp (130 kW) and 1,700 kg weight, driven in a sporty manner, there is far greater wear on the tires. Top of the list in terms of wear are sports cars like the Porsche Carrera 911. Although at 1,400 kg this super sports car is relatively lightweight, its 320 hp (235 kW) wrench at the tires so much that there is bound to be extreme wear on them." Rough road surfaces and a sporty driving style further aggravate tire wear. If, in addition to this, the temperature falls below seven degrees, the wear on summer tires rapidly increases.

"Modern tire compounds show the lowest wear when they are

used in the temperature range for which they have been designed" is how Dr. Lange summarises the results of Continental's latest study. "It is generally known that winter tires forfeit around ten per cent of their mileage performance if they are driven in the summer. However, with summer tires that stay on the car throughout the winter, the fact that the compound freezes means that wear is substantially higher. Our tests here have shown up to 20 per cent more wear than in summer use."

Dr. Lange's advice is to systematically switch between summer and winter tires: "This means greater safety and, as we have seen in our study, extra mileage performance. By switching to winter tires you also do your wallet a favour."

"The continuing trend towards specialisation in tires has very positive benefits for the motorists" comments Dr. Lange. "These include safer driving characteristics on wet and dry roads, short braking distances and low rolling resistance. In their respective temperature ranges, summer and winter tires offer optimum performance and thus the lowest wear."

The Continental Corporation is a leading supplier of tires, brake systems, chassis components, vehicle electronics and technical elastomers. Consolidated sales in 2003 amounted to €11.5 billion and employees currently number approximately 73,000 worldwide.

The Tires division is an Official Partner of the 2006 FIFA World Cup GermanyTM. Further information is available at www.conti-online.com and www.contifanworld.com.