Fuel-efficient tyres

Manufacturers are using chemical additives to make greener tyres

JOHN DUNLOP had a son who complained that his bicycle was bumpy to ride. So he invented the pneumatic tyre in 1888. Various improvements have been made since then. In particular, Pirelli, an Italian tyremaker, introduced steel-belted radial tyres in 1973. These reduced the fuel consumption of cars fitted with them. Now manufacturers are trying to develop tyres that reduce that consumption still further.

Tyres account for about a fifth of the energy required to power a car. They provide friction, so that the vehicle can grip the road, but some of the power supplied to the tyres is then lost as heat. Indeed, Michelin, a French tyremaker, estimates that this “rolling resistance” accounts for 4% of the world’s carbon-dioxide emissions. Tyre designers have therefore sought to improve fuel economy by reducing rolling resistance. However, this not only reduces a tyre’s ability to grip, making drivers take corners sideways, it also wears out the tyres more rapidly.

Such disadvantages may now be overcome using chemical engineering and the clever design of new materials made from tiny structures just a millionth of a metre across—dubbed “nanocomposites”—along with elaborate structures known as “metamaterials” that let engineers build microstructures into tyres. Such innovations could, for example, enable the inner lining of a tyre to have a special coating that helps retain air longer, while the tread would contain a compound that lets it provide the right amount of traction where the rubber meets the road.

Over the past few years, some tyremakers have routinely added polyester, fibreglass and silica particles to the mix used to make tyres, in order to increase the durability of the finished item. A modern tyre contains up to 30 different materials, including synthetic polymers such as styrene-butadiene rubber, according to Forrest Patterson, Michelin’s technical director in America. A “durable security compound” incorporated into the treads of the company’s new Energy Saver tyre helps maintain the tyre’s rigidity, allowing it to grip the road. The performance of tread rubber depends strongly on the quality of the molecular bonds formed by the 14 individual ingredients that go into making the rubber, and Michelin claims to have perfect control of these molecular interactions. Mr Patterson says that the tyres will increase fuel efficiency by 8% compared to standard tyres, and will reduce a vehicle’s carbon-dioxide emissions by almost a tonne over the tyre’s lifetime.

Goodyear, an American tyre manufacturer, recently announced that the 2010 model of Toyota’s popular Prius hybrid car will be fitted with its Assurance Fuel Max fuel-efficient tyres, which also contain a special compound in their treads to help reduce fuel consumption. The company estimates that, over the life of a typical tyre, it will save its owner enough petrol to drive more than 4,000 extra kilometres (2,500 miles). The 2010 Ford Fusion and the 2011 Chevrolet Volt models will also be fitted with this tyre.

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Tags: fuel economy, fuel efficient tires, green tires, metamaterials, nanocomposites, rubber meets the road, styrene butadiene rubber

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