Kristen Stewart leaves “Twilight” far behind in a sexy, adventurous performance in “On The Road,” based on the iconic Jack Kerouac novel, where she “pushed herself” hard, she told the media at the Cannes Film Festival on Wednesday.

In the film directed by Walter Salles (“The Motorcycle Diaries”) Stewart appears topless and close to fully naked in several scenes. She plays Marylou, the wife of one of the writers who joins them on their road adventures.

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In one particularly raunchy scene, she is sitting in the front of the car between the Kerouac-like character Sal Paradise (Sam Riley) and her husband Dean Moriarty (Garrett Hedlund). Filmed from behind, all three are topless with the implication is they are all naked.

“I wanted to do it,” she said when asked about it at the news conference. “I love pushing, I love scaring myself.”

Brazilian director Walter Salles spent eight years trying to bring Kerouac’s free association prose to the screen, criss-crossing the U.S. for over 60,000 miles.

It’s a movie that Kerouac himself tried to make in 1957, when he wrote a letter imploring Marlon Brando to buy his book and play the character of Dean Moriarty, based on the legendary Neal Cassady, opposite him.

‘On the Road” by Kerouac was one of first unbridled expressions of rebellious youth culture in post-war America. The Beats – with Allen Ginsberg and Kerouac as their leaders – paved the way to the cultural rebellion to come later in the century.

The film is atmospheric rather than plot-driven, featuring endless, languorous scenes of people smoking cigarettes, Paradise sitting at his typewriter and Paradise hugging his buddy Moriarty.

Salles explained at the news conference that he organized a month-long beatnik “boot camp” for the cast in Montreal in 2010 to familiarize his twentysomething stars with the Beat Generation, a time as unfamiliar to some of them as the Edwardian era. 

But given the 30-plus years that have elapsed since Francis Ford Coppola bought the rights in 1978, the boot camp was not just a smart idea, it was a necessary one. 

The normally truculent Stewart, who plays the freewheeling, sexually adventurous Marylou, spoke passionately about the experience.

Like co-stars Riley and Hedlund, she was so committed to the film that they all agreed to stay on even after the production was delayed by several years.

"It all started in Montreal,” she said. “I'm usually self-conscious about running around town with my face hanging out. But I got to live more in those four weeks than I ever usually do in my life.”      

Salles rounded up Beat scholars like Kerouac biographer Gerald Nicosia, who brought hours of audiotapes, and persuaded Cassady’s son John and the daughter of Luanne Henderson to speak to the cast. He also screened movies like “The Exiles,” which was shot in 1958, and documentaries with jazz greats like Charles Mingus to give the cast a sense of the time period.

 “This is not a story about the Beat Generation,” Salles said. “It’s about the story that precedes it. It’s the beginning of a social and political awakening in what was then a very conservative country. We have a lot of images from the Beat Generation when they were all in their 30s but those are misleading.  We’re seeing them when they had completed their journey. This film shows them going from their youth to early adulthood.”

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Hedlund also took a trip to San Francisco with Salles to interview John Cassady.

“I took a notebook and listened to him talk,” said Garrett. “It was very beneficial.”

Kirsten Dunst, who plays Cassady’s second wife, Carolyn, and Viggo Mortensen, who plays a character based on William Burroughs, were cast too late to attend the Montreal boot camp. Dunst said she read Carolyn Cassady’s memoir, “Off the Road” and “based my choices on that.”

Mortensen said he re-read “On the Road” after first reading it at the age of 17. “It made me realize how pertinent it is today,” he said. “We may have had to wait 30 years to bring this book to the screen but I think it was worth the wait. It’s a great time for it to come out.”

The movie screened in competition, and will be released in the fall by IFC Films and Sundance Selects.