Lance Armstrong, rising gasoline prices, and America’s love affair with the body beautiful have helped to launch a boom in bicycle sales while the number of cars sold has slumped.

Sales of speciality bicycles have soared by 10% so far this year while car sales are down by 9.5% in the same period. As if to confirm the apparent new trend towards eco-friendly transport, the energy secretary, Samuel Bodman, outlined a national oil conservation campaign yesterday.

Americans were asked to rein in their gasoline consumption to compensate for disruption to oil supplies caused when Hurricanes Katrina and Rita roared through the Gulf of Mexico.

Mr. Bodman issued his plea only days after President Bush, himself a keen mountain bike rider, urged the country’s motorists to share cars and drive less.

Even before the latest campaign, Americans bought almost as many bicycles (19 million) last year as they did during the 1973 oil crisis (20 million).

The increase in petrol prices by almost 50% over the past year has been the main reason behind the switch from four- to two-wheels. But it is not the only explanation for the change.

“Above all, it’s the higher price of gas,” the owner of Scooter Commuter in Bethesda, Md., Paul Gaiser, said. “But also it’s concern for the environment and the cost of another car.

“Our sales have quadrupled in the last two months. I think it’s a major paradigm shift. It’s here to stay.”

The pedalling boom brought sales of more than $5 billion in 2004, mostly in the cheap hybrid road bike sector in which the Wal-Mart and Kmart chains specialize.

The bicycle is also becoming increasingly popular among those concerned by America’s obesity crisis. With 130 million Americans overweight, anything that tightens the waistband is commercially appealing.