At the annual International Isle of Man TT (Tourist Trophy), motorcycles reach speeds of about 200 mph on twisting, narrow open roads.

The festival, which is often called the most dangerous sporting event in the world, has claimed the lives of more than 200 riders. At the time of writing, two motorcyclists – Bob Price and Karl Harris – have died riding in the 2014 TT fixtures.

The statistics do nothing to deter William Dunlop; this week marks the Northern Irishman’s eighth appearance at an event that many folks regard as nine kinds of crazy.

“Lots of people think it looks dangerous,” he tells me. “And lots of people say ‘Well, that’s just insane’. But horse-racing has as many deaths as road racing. People assume bikes are more dangerous because they look more dangerous. But when you look at the odds it’s not too bad.”

He couldn’t sound less afraid. But the people who enjoy base-jumping and bull-running and heli-sking probably say something similar. When William sees other extreme sports, does he recognise the dangers? Or is he an all-round daredevil?

“It’s a bit weird, like,” he laughs. “I would never jump out of an aeroplane with a parachute or anything like that. I couldn’t do it. It looks insane. But everyone to their own.”

You have to feel tickled by the contradiction: William has recently taken up Mixed Martial Arts training but doesn’t want to fight bouts “because it looks a bit sore”.

Is there a method to the TT other than ‘hang on’?

“At the Isle of Man you go as quick as you can right from the start. You need it for your confidence. It’s just the way of the race.”

William and his brother Michael are the second generation of Dunlops to excel at the sport. Their late father, Robert, enjoyed five TT wins and a record-breaking 15 North West 200 wins. Their uncle, Joey, was five times World Motorcycle Champion with 24 Ulster Grand Prix wins, 13 North West 200 wins and 26 Isle of Man TT wins. Both died in racing accidents.

Quick translation for the road racing illiterate: they are all awesome motorcyclists.

Was there ever a chance that William would do something else?

“Well, I was very late to start,” he says. “I was maybe 18 which is a good old age to start at this. I would love to have played football or something. But I just wasn’t good enough. So I thought I’d give the bikes a try.”

But those are some mighty big shoes to fill. It can’t have been easy to gear up for the first time with that surname attached, can it?

“It wasn’t too bad at the start. It wasn’t a bother because you’re learning as you go. And you’re learning a lot. There’s far more pressure now.”

The two generations of Dunlop brothers – William and Michael, Robert and Joey – are the subject of Road, a thrilling new film written, produced and directed by Diarmuid Lavery and Michael Hewitt.

There’s a lovely contrary alchemy about the project. The quiet, professional Dunlop family are all about keeping their heads down, both literally and figuratively. They are unlikely to ever be confused with the Kardashians. I wonder what the co-directors did to coax William and Michael in front of a camera?

“We didn’t think it wasn’t going to be the film it is now,” admits William. “We just thought they were going to follow us for a year. We thought it was just about the bikes. They went down a different route with the film. But I think they did a great job.”

Road arrives in cinemas with everything one could ask from a sports documentary. Mark Garrett’s splendid cinematography brings the viewer electrifying close to the tarmac. Bikes trill between snatches of Mark Gordon and Richard Hill’s compelling score and Liam Neeson’s narration. Joey and Michael Dunlop’s extraordinary rise from the back roads of Ballymoney, Co Antrim, to world domination in their field makes for an engaging sporting underdog narrative.

But the Dunlop story is defined by tragedy as well as success. Road recounts gruesome injuries and fatalities, including the deaths of Joey, who died in Estonia in 2000 while leading a 125cc race, and of Robert, who died at the North West 200 in 2008. Grieving family members, including William, provide poignant, sorrowful testimonies.

“There were some things I wish they hadn’t seen and I wish they hadn’t filmed,” says William. “But it turned out well because I think people sometimes just see you as millionaires or whatever. But when they see this and the hard time you have, just to get by, maybe they’ll think there’s more to it.”

In the hours following Robert Dunlop’s death, his son Michael retreated into the shed and starting working on his bike. He went on to win the North West 200. Tragedy seems to spur on, rather than deter the Dunlop boys.

“I wouldn’t say it spurs us on,” says William. “It doesn’t stop us I suppose. There’s no point worrying about it or crying about it. If it happens, it happens. And you just have to get on with it. There are plenty of other people who have had harder times than us.”

Unsurprisingly, a recurrent theme in Road is the need for speed. Neither Joey nor Robert seemed capable of quitting road racing. In the film, we see William talking about life at 200kph as a ‘life without worries’. Life in the off-season must get a bit dull, surely?

“Not anymore,” says William. “Since it became a job, I really enjoy off season. I’m happy to stay away from it. I’m happy to play a bit of golf. I’m happy to do different stuff. I enjoy the off season now more than the season itself.”

And when the next Dunlop generation decides – as they undoubtedly will – to straddle motorbikes in earnest, what will William say to them?

“It’s a good life,” he says. “Everybody sees the hard side of it, but it is better that than drinking around the streets every weekend and acting the maggot. There are perks. You get to travel. You get weekends away. You get to be in a documentary.”