Teenager crusades for proper tire pressure.

ODESSA, Fla. - When you're 13, like Savannah Walters, and the world is your oyster, you can do more than try to become an Olympic equestrian ? you can also try to change the world. "The future is what I'm worried about," says Walters, "the future of all wildlife, all people and our planet." Walters was shocked to learn how careless American motorists are: Of 300 million tires produced here annually, the Rubber Manufacturers Association says an estimated 85 percent are driven with too little air.