Sooner or later, the cars in the Fast & Furious movie franchise will go out of this world.

This has become the running joke among its producers because every new movie in the franchise has consistently one-upped its previous instalment with its action stunts - from cars dropping out of military planes in the air to racing a Dodge Charger down the streets with a massive bank vault attached to the back.

In the eighth and latest instalment of the series, Fast & Furious 8, which opens in cinemas on Thursday, a submarine pursues in icy waters a Lamborghini and a tank, among other vehicles.

How could the film-makers top this in the next movie?

Chris Morgan, who has written every movie in the franchise since the third instalment, Tokyo Drift (2006), says with a grin: "People have said it as a joke probably once at every meeting, that we should have cars in space or something. But it has not happened yet."

Jokes aside, he is insistent that audiences continually turn up in droves to watch the movies not just because of the outrageous vehicular stunts.

"The reason audiences keep accepting these stunts in our movies is because they care about the people inside the car. You're worried for them, you're excited for them and you're with them. Spectacle will get you only so far."

And audiences care for the characters, he adds, because of the franchise's oft-repeated theme of family.

"What Dom has been preaching in the films is family, family, family - that's the code you stick to, no matter what. People respond to that," he says of lead character Dominic (played by Vin Diesel).

Producer Neal Moritz concurs, saying: "We're very careful when we make a new movie that we're not saying, 'Oh, let's just do bigger stunts.' If the stunts don't come out of the characters, or are organic to the series, then it's wrong and will just destroy the franchise."

They were speaking to The Straits Times and the regional media at an interview session held in Beijing, where they were promoting the film alongside director F. Gary Gray, British actor Jason Statham and South African-born Oscar winner Charlize Theron.

In the new movie, which is called The Fate Of The Furious in the United States, the actress plays Cipher, the first female villain in the franchise.

Although she is never seen driving the fast cars, she has the power to remotely control almost any machine or vehicle.

In one scene, she uses a tablet computer to send hundreds of stationary cars flying out of a multi- storey carpark and crashing onto the streets below. This is a nightmare scenario for countries around the world on the cusp of self- driving cars going mainstream.

Portraying Cipher has made Theron, 41, more wary of technology than before, she says.

"I've been paranoid about technology for a very long time. Technology in the wrong hands can be very dangerous.

"It's a good thing that I'm not from the generation whose whole life has to be on the computer. If you hack me, you'll just find a lot of pictures of food and of my kids playing with each other," says Theron, who is single and has two adopted children aged five and 11/2.

Her role of Cipher is just one of several tough-as-nails characters she has taken up recently, along with fierce warrior Furiosa in Mad Max: Fury Road (2015) and slick super spy Lorraine in the upcoming action thriller Atomic Blonde.

Theron, who won an Oscar for playing a serial killer in Monster (2003), says, however, that she sees them as a lot more complex than just lean, mean fighting machines.

"They're all somewhat broken in a real sense in order to do such crazy or unthinkable things. And I like that about these characters.

"They allow you to play on a much bigger field and on a much bigger scale. I'm not taking away from anything I've done in the past, but I'm definitely enjoying this new phase, exploring a different kind of storytelling and utilising my body in a way that I haven't done since I was a dancer," says Theron, who was a ballerina who had trained at the famous Joffrey Ballet School in New York.

She is intrigued by the character of Cipher despite not being able to explain the villain's motivation.

"I've actually talked to Chris a lot about this when we were developing the story and he said to me, 'Isn't it more frightening when you don't know why she does all these things?'

"And I guess that's right. People in good conscience always want to know what motivates someone to do something. But for someone like Cipher, who is a complete psychopath, she just wants to be a superpower and that's scary."

Besides Theron, another fresh name on the project is director Gray, who takes over the helm from Malaysian-born director James Wan (The Conjuring, 2013) and Taiwanese-American film-maker Justin Lin, who made some of the previous films.

The 47-year-old, who is known for making films such as action- flick The Negotiator (1998) and rap music biopic Straight Outta Compton (2015), says: "When I was first asked to join the movie, I was like, 'How fantastic', because I'm a fan of the series.

"And then I was like, 'Oh my god', because it's a big movie and it's such a massive responsibility taking over, given the franchise's global popularity."

Since the first movie in the franchise was released in 2001, the series has become one of the biggest hits at the global box office.

The previous film, Furious 7 (2015), is the sixth highest-grossing film in the world, with more than US$1.5 billion in worldwide ticket sales. In the mega film market that is China, where Hollywood is increasingly trying to make its mark, that movie ranks as the highest-grossing film there, with US$390 million in earnings.

To match up to those expectations, Gray had everything from a Lamborghini to a tank transported from the United States to Iceland.

He says: "You know, it was crazy, but it all came together. The team behind this film did the impossible.

"We were drilling the ice in Iceland every single day to check the depth, in case the ice collapses, because we were shooting racing scenes on the ice. The level of engineering and science is on a whole new level for this movie."

The film's leading man, action star Diesel, certainly appreciates what Gray has done with the film. At press interviews, Diesel, 49, has been telling journalists that he believes the director deserves an Oscar for his efforts here.

Gray bursts out laughing when he learns of this.

Many critics think he was snubbed at the Oscars last year because Straight Outta Compton, a biopic of rap pioneers NWA, should have earned him a nomination for best director.

Gray says: "You know what, I don't do these things for the awards. I don't look at awards and badges and that kind of thing.

"I just think about whether the audience can connect to my film. If we get the accolade, it's the icing on the cake. But it's not the cake."

•Follow Yip Wai Yee on Twitter @STyipwaiyee

•Fast & Furious 8 opens in cinemas on Thursday.