Exclusive: ‘Rush’ Trailer Features a Drastically Slimmed-Down Chris Hemsworth

The opening of the cockpit for a Formula 1 racecar is required to be a maximum of 850 millimeters long (about 33 1/2 inches) and 520 millimeters wide (20 1/2 inches). So how are you supposed to fit a Norse god inside one of them?

That was the problem faced by Oscar-winning director Ron Howard in making his new movie, "Rush," the true story of a rivalry between two F1 drivers that electrified motorsports fans in the mid-1970s. To play the tall, blond, and brash British racing legend James Hunt, the director cast tall, blond, and brash Australian actor Chris Hemsworth, best known to audiences as the hammer-swinging Marvel hero Thor. But to turn the god of thunder into a titan of speed, Hemsworth had to trim down his world-famous "Avengers" physique.

"[Chris] is the height of James Hunt, and they’re both 6-3," Howard said in a phone interview with Yahoo! Movies earlier this week. "But he had to slim down drastically. And in kind of a no-muss, no-fuss way, he put himself through a pretty remarkable regimen, and got himself to James Hunt's size."

That meant Hemsworth went quickly from the bulked-up size he was at for "Marvel's The Avengers" (topping out at a reported 235 pounds) to James Hunt's slimmer build (the real driver weighed in at around 175 pounds).

The effort worked, and Hemsworth was able to slip into the narrow confines of an actual F1 car to drive it on film. "We did nothing to the car to make it so that he could fit in," Howard said. "He just got lean and like an F1 driver."

Watch the exclusive trailer for "Rush" below, and keep reading to see how much race driving Hemsworth actually did himself, and just how dangerous filming actually got.

"Rush" reunites Howard with screenwriter Peter Morgan, who wrote the Oscar-nominated "Frost/Nixon," and this is another true story set in the '70s about a bitter rivalry that turns into begrudging respect. Except this one takes place at 180 mph.

The film is set during the 1976 F1 championship season, as controversial Brit Hunt (Hemsworth) battled with German driver Niki Lauda (played by "Inglourious Basterds" star Daniel Brühl) for supremacy. But at that year's German Grand Prix, Lauda had a horrific accident, suffering severe burns on his face. Still, within weeks Lauda was back on the track, dueling with Hunt all the way to the final finish line.

Howard said to prepare for their roles, both Hemsworth and Brühl attended intensive driving schools to learn how to handle real racecars. Then they spent another two weeks rehearsing on the track to master the moves they would need to recreate on camera.

"Of course, those things are dangerous," Howard said, "And the scenes we were throwing them into were particularly dangerous." So the scenes that called for top speeds were done by stunt drivers. But, Howard explained, the actors "had to get good enough so that they could come tearing into the pit stops and then accelerate out. And that’s around people, and that’s harnessing the power of those machines in a situation that really requires precision." He said that Hemsworth and Brühl did get their cars up to speeds around 100 miles per hour, but "the cars go 180."

Howard said filming fast cars and breakneck action reminded him of his directorial debut, the 1977 Roger Corman-produced "Grand Theft Auto," though safety standards have definitely improved over the course of his four-decade career. "I had flashbacks of those Roger Corman days," Howard said, "And thank God we didn’t flip any cars and/or T-bone anything like we did in 'Grand Theft Auto.'" Howard noted that while no one got hurt on his first film, its stunt coordinator, Vic Rivers, did die in an on-set accident the following year, "so none of this is to be taken lightly."

Howard said that the high-risk environment of filming "Rush" recalled another fiery flick of his, 1991's "Backdraft." "I remember heaving a tremendous sigh of relief when we wrapped 'Backdraft' and there were no serious injuries, and I felt the same way about 'Rush.'" That wasn't to say the shoot was entirely without incident. "We had some mishaps," Howard said. "We had some spinouts and a couple of light moments where there’s some contact and things could’ve been a lot worse but they weren’t."

The filmmaker revealed that the driving team they assembled for the film was so good, in fact, they were able to capture much of the racing action with real cars and not special effects. He said they filmed more precision driving -- "dangerous overtakes and hairpins… wheel-to-wheel bumps, [and] touching" -- than he ever expected they could ever do safely. "And I’m glad to be able to underline the word 'safely' because [there were] no injuries.'"

Hunt, the driver played by Hemsworth, died in 1993 at the age of only 45 after a sudden heart attack. But Niki Lauda is still alive, and he even took Howard out for a spin on the Ferrari test track. After Hunt retired from racing, he became a popular racing commentator in the U.K., and Howard said that Hemsworth poured over tapes to capture both the real racer's accent and his attitude.

"Every once in a while Chris would improvise a line, and I'd say, 'That's hilarious,'" Howard recalled. "And he'd say, 'No I just got that from the documentary. James said that.' So he had a little list of James comments that were hilarious and raw and sexy that he was always trying to work into the script."

You'll be able to see the slimmer and much faster Hemsworth on the big screen when "Rush" opens on September 20.