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As cheap thrills go, we've always considered gravity racing to be just below watching the excrutiating creep southward, through traffic, of Manhattan's M5 bus. Having the lamest Cub Scout franchise in history, our Pinewood Derby meets were just the three of us, rolling Matchbox cars off the hood of some guy's '78 Malibu in the A&P parking lot. Soap Box Derby? Right. Shopping carts down Main Street. But now, there's a whole racing series devoted to sans-engine racers. And the car builders are more NASA than Mattel. In fact, Volvo created its conceptual 2005 Extreme Gravity Car to race in one such event, to be held this August 18 at Jack's Peak in Monterey, CA. Sporting a fiberglass body and steel chassis, the car will hit downhill speeds of more than 70 mph. A set of ceramic brakes make sure it won't fall off the hood of the Malibu. (Note: it also ran one in 2004.)