In the race for medal supremacy this summer the U.S. has tried to stave off the competition by creating a world-class practice course at the Olympic Training Center in Chula Vista for riders in bicycle motocross (BMX). That event makes its Olympic debut in Beijing and features races among eight riders who bump, jump and knock elbows for position on a quarter-mile rolling, banked dirt track.

Since Americans often dominate the sport, the Chinese designed and began their Olympic training on a so-called supercross course, far gnarlier than ones on the international circuit. The start hill, a six- to 12-foot drop on a regular BMX track, will be 30 feet high in Beijing. Speeds will reach 40 mph at the bottom of the course, almost twice as fast as on a more traditional layout. "It's jaw-dropping," says U.S. rider Donny Robinson, a 2006 world champion, who won the Beijing test event last August. "Unless you know what you're doing, you're seriously out of your element."

After seeing the Olympic course, the USOC and USA Cycling constructed a $500,000 run with identical specs at the Chula Vista center, a 150-acre site just south of San Diego that is a training ground for archers, canoeists, softball players, track and field athletes, and many others. Though BMXers have competed on temporary supercross tracks over the years, the Chula Vista course, which opened in January, is one of three permanent ones in the world.

The U.S. riders appreciate the help to prepare for some wild rides in Beijing. "On a regular BMX course, you can sort of roll through a jump," says Kyle Bennett, the current world No. 1. "With [the Olympic course], you're committed to [flying off] the jump because of the height and speed. Fans will trip out when they see it."

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