David and Dennis Head enjoy living the high life. After a long day at Head Inc., a 60-employee manufacturer of custom brass fittings -- a family business they run with their uncle Mike -- the 35-year-old identical twins often tug on helmets, hop aboard their matching dirt bikes with 250cc two-stroke engines, and fly off around their own motocross course. Fashioned by a professional track builder, the four-tenths-of-a-mile circuit features small spine-jarring bumps called rockers and a takeoff ramp that rockets them into the air. "It's like skydiving," says David of the four seconds of hang time, "except without the parachute."

The entrepreneurial daredevils have long been extreme sports lovers. As teenagers, David served as Dennis's one-man pit crew at motocross races -- one of which left Dennis with a fractured skull, another with broken vertebrae. These days, the life insurance policies backing their stakes in the business, which is based in South Elgin, Ill., prohibit them from competing in sanctioned races (not to mention skydiving and bungee jumping). But the policies don't bar going airborne on their own property and busting such X Games moves as the Superman, where they stretch out horizontally from the handlebars, stomach on the seat, legs extended behind them. Nor do the twins feel they must pass up an annual snowmobile race across a 500-foot-wide span of the nearby Fox River -- a race held in autumn, months before the river freezes. Dennis says his extreme pursuits are actually quite tranquil. "If you're golfing, you're maybe talking about work," he says. "But when you've got a two-stroke revving, you don't talk. You don't think. It's relaxing."