Then they must brake – hard – and take a ninety degree left, while conserving as much momentum as possible. It’s a dangerous, demanding obstacle and the centre piece of the Lisbon Downtown, mountain biking’s equivalent of the Monaco Grand Prix.

For Team G Cross Honda, the Lisbon Downtown offers a unique opportunity to bring the sport of downhill mountain biking to the people. The trees, dirt and rabbit holes that mark a typical course are replaced with stone walls, cobbled streets and the occasional pot plant. The riders race against the clock from the top of Lisbon’s beautiful old town to the bottom, and victory margins will most likely be measured in tenths or even thousandths of a second.

The paddock is situated at the bottom of the hill and is a mass of toned bodies and garish race suits. The lavish motorhomes of Formula One are missing, but the atmosphere is friendly, relaxed and convivial. No one doubts the intensity of the competition, but when the racing’s over, the riders will chat and high-five. Team G Cross Honda is camped in three paddock tents, pitched beside a van full of spares. The team’s lead rider, Greg Minnaar, is one of the favourites for victory today and there is a quiet air of authority as the mechanics go about their work. Martin Whiteley, the Team Director, is attending to the details and looking after his riders.

Last year, the team won the World Cup – the equivalent of the F1 constructor’s championship. This was a triumph made possible by the brilliance of the riders, the professionalism of the team and the performance of the Honda RN01 bike.

“It’s not just a matter of putting a sticker on an existing bike,” explains Whiteley. “Honda’s engineers looked at the sport and asked: ‘how do we do bikes?’” What began as a pet project for members of Honda’s motorcycle division in Japan has grown into a highly successful sideline that challenges and inspires the best engineers. “In Honda, the RN01 has a unique position,” continues Whiteley. “This is the only Honda without an engine. RN is for ‘Racing Nature’ and the G in G Cross stands for ‘gravity’.” This is a clean, green sport - the only carbon emissions produced during a race are those of a panting athlete.

The RN01 has pedals, wheels and handlebars, but that’s about all the RN01 has in common with a traditional push-bike. The gearbox, for example, is crafted from carbon fibre, just as it is on a Formula One car. Instead of a conventional derailleur, the RN01 locates its seven ratios in a carbon fibre box between the pedals. Gears can be selected without the rider having to pedal, which can prove invaluable on a downhill course.

“The riders can pre-select gears using a switch on the handlebars,” explains Mike Van Zyl, head team mechanic. “Our system is more reliable than a derailleur and there’s no chance of the chain jumping off.” No less impressive is the Showa rear suspension system, which features a form of launch control. Greg Minnaar takes over. “We can lock the rear suspension for up to ten seconds,” he says. “This prevents the losses associated with suspension compression.” Minnaar also talks me through the multifarious tyre choices available to the rider. Selecting the right tread and compound can be of critical importance.

Minnaar is cool, urbane and, in his own words, “pretty ripped”. Downhill racers might have gravity on their side, but they must also have an exceptionally high level of strength and fitness. In some ways the sport is similar to downhill skiing and no-one says they have it easy.

The South African is a double World Cup Champion – the equivalent of the F1 World Championship – and it’s fascinating to compare him with the team’s lunch guest, a certain R. Barrichello. Both are physically fit, wealthy and have been at the forefront of their sport for a number of years. Barrichello tries the ’bike and admits that there are “several drivers that I would like to run over on one of these.” He admits to being “more of runner than a cyclist,” but likes “anything to do with speed. My weekends are full of exercise and watching racing. I’ve been impressed by the tech of the bikes, but my contract wouldn’t allow me to do this sort of thing. These guys are crazy.”

The dangers of this sport are self-evident. In Lisbon, the riders will top 50km/h over jumps on cobbled streets where the only crash barrier is a solid stone wall. “I’m nervous because I want our riders to do well,” says Whiteley. “But I also want them to stay safe. They need to be able to compete for the rest of the season.”

Injury is an occupational hazard. The team’s third rider, eighteen year old Brit, Brendan Fairclough, is a frustrated spectator in Lisbon, having fallen and damaged the tendons in his right wrist. Matti Lehikoinen, the team’s Finnish rider, has had three operations on a broken shoulder, but is “90 per cent OK” and is competing today. In the early afternoon, Barrichello and I watch the semi-final and our attention is drawn to the so-called ‘hot seat’. The rider with the fastest time sits in a giant throne and wears a plastic crown. But the moment his time is beaten, he must vacate the chair. “That’s great,” says Barrichello. “They should introduce that for qualifying.” The F1 driver is also eyeing up the bikes. “I’ve been told there are only eight in the world, but I’d like to order the ninth,” he says, half-joking.

Qualifying goes well, with Minnaar second fastest behind Steve Peat, who has won this event for the past five years. The Honda rider reckons there is more speed to be found and as we gather to watch the final, there is a buzz of expectation. “C’mon Greg,” says Martin Whiteley, as if to himself.

Lehikoinen is the first of the Honda riders and puts in a personal best performance. It’s the quickest time thus far and he takes his place in the hot seat. But then his time is beaten and the focus of attention switches to Minnaar.

The TV director catches up with the Honda rider near the top of the run, just as he leaps an SUV, parked lengthways to the course. Minnaar lands neatly on the cobbled streets, swings left, dodges a traffic bollard and launches himself down some steps. “He’s at 110%,” says Whiteley, as Minnaar deliberately bounces his rear tyre off a stone wall to change direction. “This is everything he’s got.”

Minnaar rounds a tight hairpin – made possible only by performing an intricate wheelie – and pedals furiously to build up speed. “You need lots of power to do well here,” says Whiteley. “And it’s all about how you put the power down.” Needless to say, there’s no traction control. There is a flash of silver as Minnaar launches himself off the jump that doubles as a (literally) flying finish. Eyes focus on the race clock, which tells a heart-breaking story. Minnaar is several seconds off the pace. “Something must have happened at the very top,” says Whiteley. “He must have fallen.”

We wander back to the paddock to be greeted by a disappointed rider. Out of sight of the TV cameras, Minnaar made an error within the first few yards of the start and was projected over the top of his handlebars. It was a mistake from which he could not hope to recover.

It is a disappointing end to what has been a fantastic weekend of action. Downhill mountain biking doesn’t receive the media exposure it deserves. This is a proper sport in which, like Formula One, offers an intoxicating blend of courage and technology. Engine or no engine, this is a sport that will bring out the petrolhead in everyone.