In 1971, the Academy Award–nominated documentary On Any Sunday captured the then-uncharted world of off-road motorcycle racing. Watching it today, it's impossible not to crave those classic-looking dirt bikes scrambling across the Baja desert or careering up tree-lined Spanish trails; even the deep thrum of their engines sounds better than the whine of today's insect-like machines. Between revs, you might even recognize the film's eternally stoked director and narrator, Bruce Brown, who also made the surfing classic, The Endless Summer.

Bultaco bikes tended to be at the head of On Any Sunday's pack. Founded by the late Francisco Bultó in Barcelona in 1958 (and folded by him in 1983), Bultaco revolutionized the off-road industry, producing fast, lightweight bikes with incredible handling. A former racer himself, Bultó guided the company with the philosophy, "Sales follow the checkered flag," and it was at competitions like the International Six Day Trials in El Escorial, Spain—the setting for this clip from Brown's film—that Bultaco earned its winning reputation.

Although this segment focuses on the legendary American racer Malcolm Smith and his trusty Husqvarna, most of the Spanish riders (in the canary-yellow helmets) are astride Bultacos. It was on El Escorial's trails that Oriol Puig Bultó, a company engineer and Francisco's nephew, honed his riding skills. He would become Team Bultaco's winningest motocross rider.

"The spirit that was in Bultaco has never been duplicated," Oriol recently said.

Whether you're watching an 'Old Bull' on the charge or admiring the bike's fluid beauty as it rests, quiet and riderless, between races, you would be hard-pressed to disagree.— MICHAEL MRAZ