As the cable cars that connect downtown Medellín – Colombia’s second city – to the hillside slums pass overhead, a band of teenage cyclists have gathered at the side of the road. Vallejuelos is a downtrodden neighbourhood, rife with crime and unemployment, but “gravity biking” is helping some kids escape their troubles.

As the name suggests, gravity biking involves steep descents. Enthusiasts strip a typical bike to its frame and build it back up from scratch. To improve descending speed (which can reportedly reach up to 77 mph), riders weld weights to their contraptions. Pedals are superfluous: to climb the hills riders hang on to passing trucks, sometimes using homemade hooks on a line.

Estiven Hurtado is an avid gravity cyclist and has lived in Vallejuelos his whole life. “We live for gravity biking here,” he says, lugging his modified bike behind him, emblazoned with the visage of the drug lord Pablo Escobar, Medellín’s most infamous son. “It’s a way of life for anyone who lives up in the communes.”

Gravity biking can be found across Colombia, but it is most popular in Medellín and surrounding towns owing to the steep Andean mountains. But the nascent sport is as dangerous as it sounds, and last year one nearby town, La Ceja, banned it outright.

Pablo Escobar is a popular leitmotif for Medellín’s gravity cyclists.

“Given the grave danger, the decision was made to prohibit the circulation of bicycles modified by hand for this sport throughout the territory,” said La Ceja’s council at the time.

Hours after meeting the Guardian, Hurtado is left injured at the side of the road after colliding with a motorcyclist on a tight bend down the hillside. Almost everyone who practices gravity biking at some point ends up in a similar situation.

“It’s the risk we run around here, but we get used to it,” says Marlon Muñeton, who at only 16 is seen as a leader among the gravity biking community. Shortly after the BBC published a video of his exploits last month, he had an accident, narrowly escaping serious injury and doing irreparable damage to his bike. He had twice before been gravely injured after crashing, nearly dying both times. His shaved head carries several scars.

His mother, Jessica, speaks for much of the community. “They are fools the way they hurtle down the highways,” she says in her ramshackle single-room home overlooking the city. “Just look how many scars they all have.”

The pastime has exposed fault lines in the neighbourhood where crime and unemployment are rampant. Criminal gangs and drug traffickers control much of Medellín’s slums, and Estiven Hurtado’s bike was confiscated by one of their members after his crash.

“These kids often come from broken homes, and often fall into drug abuse,” says Natalia Montoya, a psychologist at the local school. “It’s a self-destructive way of escaping the reality of their lives.”

Three cyclists from Vallejuelos have died this year, with accidents a regular occurrence. Montoya’s school, where most of the children in the neighbourhood study, engages in campaigns to encourage rider safety, donating helmets. One particular issue is the practice of pillion riders, who are at more risk due to not being in control. Lights are almost never used.

Biker Juan Pablo Morales, whose face bears the scars of a recent high-speed wipe out. “It’s not the first and it’s not the last,” he says.

“If done safely, it is a good outlet for all of the stress that they have,” Montoya says. “But there is still a lot more to do.”

Riders prefer night-time as the roads are less busy, allowing them to pick up greater speed.

Despite the risks, and despite regular altercations with the police who patrol the highways, it looks like gravity biking is here to stay.

As night falls, one group of riders waits at the roadside for a truck to latch on to. Among them is Juan Pablo Morales, who just a week earlier fell from his bike, badly grazing his face and chin. The accident has done little to dissuade him.

“It’s not the first and it’s not the last,” he says, grinning broadly. “It’ll take the most serious accident possible to stop me.”