PHILADEPHIA: As gasoline prices hit records on almost a daily basis, an increasing number of motorists in US are following a radical driving technique designed to eke out every last mile from a tank of fuel. Known as 'hypermiling,' the methods can double gas mileage, even in gas-guzzling vehicles. Promoted on a growing number of websites, hypermiling includes pumping up tires to the maximum rating on their sidewalls, which may be higher than levels recommended in car manuals; using engine oil of a low viscosity, and the controversial practice of drafting behind other vehicles on the highway to reduce aerodynamic...