Losing their grip

摘要

At the Frankfurt motor show in Germany last September, Michelin trumpeted its "low rolling resistance" (LRR) tyres, which allow a car to use less power to move. Overcoming rolling resistance accounts for one-fifth of a car's CO_2 emissions, and Michelin claims that sales of its LRR tyres so far -570 million tyres in 15 years -amount to a reduction of 2 million tonnes in CO_2 emissions through a saving of 9 billion litres of fuel per year. But the idea also rings alarm bells because lower rolling resistance should mean lower friction - and longer stopping distances.