The Croisette is not the easiest street to negotiate during the Cannes film festival. The traffic crawls crossly between the long strip of grand hotels and the prom with beach beyond. Officials cordon off stretches for long periods, tourists hub around hotel doors in the hope of seeing a star, irate journalists and film-makers jostle and shove. Scooters, motorbikes, pedalos and segways add to the melee. Protesters, musicians, mime artists and a small motorised train don't help.

So it was a measure of the affection that The Expendables cast are held in that when they rode slowly down the Croisette on two massive Soviet-era tanks, completely clogging the thoroughfare, festival-goers simply cheered them on and took out their smartphones to take a photo.

The stunt contributed to the estimated $2m bill for this weekend's promotional push, and formed the filling in a day which began with a promo of clips from the movie, and concluded with a star-studded press conference at the Carlton hotel.

This audience featured almost all of the movie's leads, including returning heroes Sylvester Stallone, Jason Statham, Arnold Schwarzenegger and Dolph Lundgren, as well as new recruits Harrison Ford, Mel Gibson and Kelsey Grammar. A producer in the showreel declared them "the best cast assembled for any film ever", while Gibson spoke of a "pile of icons".

Director Patrick Hughes explained that the cast took much pride in doing as many of their own stunts as possible, despite their advancing years, with Stallone adding: "We put the pain in and it pays off."

Ford, Stallone and Gibson at The Expendables photocall Photograph: LOIC VENANCE/AFP/Getty Images

Asked if they eased up at all as they approached their seventh decades, Schwarzenegger conceded that these days he was slammed into a padded wall rather than the real thing. "When Sly was hitting me in the face, he was taking it easy. When Harrison Ford was shooting me with a gun he didn't use live ammo."

Stallone, who has breathed new life both into the genre and his own career with the franchise, said he'd know the time had come to retire "when you wake up in the morning and you turn around and your ass falls off". That time is unlikely to come soon, however. "We are children with arthritis," he said. "We are young forever."

The atmosphere was one of macho bonhomie, both from assembled press and veteran film-makers. Stallone opined that there have been only "15 action heroes – real serious ones – in history" meaning that at least a third of them have a place in his film.

"I think the hardest thing in the world is to find [an action hero] because it's an indefinable thing that what makes the audience like a person – it's not a matter of muscles. A lot of action heroes aren't particularly muscular or good-looking; it's something that's almost intangible."

The first instalment in the Expendables series took nearly $300m at the global box office. Stallone said on Sunday he felt the second (which just beat that total) had strayed too far into irony, endangering the audience's sense of real jeopardy. "But I believe we finally got it right on the third one – kind of like marriage."

Stallone, who has been married to his third wife since 1997, also admitted that his rivalrous relationship with Arnold Schwarzenegger at the height of their fame in the 1980s had been an aggravation as well as a spur. "We are very, very similar in many ways," he said. "It's almost like [Muhammad] Ali and [Joe] Frazier. We came along at the right time in the same business. Then you get older and wiser and you realise: thank God for Arnold – he made me work harder."

Added Schwarzenegger: "That competition developed organically. And then all of a sudden it was: who has bigger muscles? Who is using bigger guns? Who is killing people in the most efficient way? Who's killing most people in the movies? It was like: 'I killed 49 people, how about you?' 'Oh I just killed 78 people.' It was a competition."

Stallone, Gibson and Lundgren atop the tank. Photograph: YVES HERMAN/REUTERS

Other actors chipped into the conversation to cheerleading effect. Antonio Banderas highlighted his happiness at the fact he was playing one of the heroes, rather than the villain he suspected his accent would typecast him as when he moved to Los Angeles 23 years ago. "That a Spanish person like me got invited to be part of a movie which is kind of a hall of fame of action heroes means a lot to my community and to me."

Lundgren kept on-message by reporting that topics of conversation on set were "dumb-bells, tequila and Sheilas", while the sole female star, Ronda Rousey, said she hankered after the "leather-wearing gun-shooting guy", as opposed to "the guys that I see walking round in skinny jeans on their iPhones".

The Expendables 3 opens around the world in August 2014. The teaser clips screened earlier today showcased exploding helicopters, slow-mo tumbles, heavy demolition and leathery A-list faces grimacing as they operated heavy artillery.