Riding along with Boorman and McGregor

Actors Ewan McGregor and Charley Boorman knew they were putting their friendship to a strenuous test when they left London and began their motorcycle trek around the world in April.

The pair’s grueling odyssey is chronicled in “Long Way Round,” a six-part limited series premiering Thursday on Bravo.

“Oh, yeah, I knew this would either cement our friendship forever or we would come out of it never speaking to one another,” Boorman recalls several weeks later, a few days after the pair reached their destination in New York. “And I can tell you very confidently today: I’ll never speak to Ewan McGregor again!”

The 38-year-old Boorman breaks into laughter at his own ridiculous notion. He and McGregor, 33, best friends since they worked together on the 1997 drama “The Serpent’s Kiss,” say they are weary but thrilled after completing the three-month, 20,000-mile trek that took them through Eastern Europe, Ukraine, Russia, Kazakhstan, Mongolia, Siberia, Alaska and Canada, followed by a final extended leg across the northern United States.

“To tell the truth, I still can’t believe that we actually made this dream come true,” McGregor says. “I think there were times when both of us wondered whether we’d be able to keep going. Parts of it were just very, very tough -- but I’m really touched to the core when I think of some of the people and places we saw together.”

“Any excuse to spend that much time on a motorcycle is great for either of us,” Boorman agrees, “but as Ewan says, it was just the friendliness and overwhelming generosity of everyone we met that made this trip so unforgettable. That’s something we can’t forget, especially given all the trouble that’s going on in the world right now.”

The journey that ultimately would take the “long way round” from London to New York started out as McGregor scanned a world map, pondering a bike trip to China, where his wife grew up.

“Then I noticed when I got to Mongolia that if I turned and headed north into Siberia instead of going down to China, it wasn’t that much farther east to the edge” of Asia, he explains.

But what appears to be a short distance on a map can translate into exhausting, patience-testing days when that area is half-charted regions with roads that are crude at best.

“Mongolia was unbelievable,” Boorman recalls. “Great parts of it are completely untouched by modern development, but the roads, when you could even call them that, were terrible and we’d find ourselves on the wrong route without any warning. There were no signs to speak of, and we had to rely on our [navigating] systems.”

The first hour of the series chronicles the extensive preparation and training that McGregor and Boorman underwent in the weeks leading to their April departure. In addition to taking exercise sessions to improve their fitness levels, they also listened to daunting advice from a “hostile environment team” that spelled out the hazards the two men would face: crooked border guards, war zones, frigid temperatures, even bear attacks.

In an interview before the trip, McGregor told a reporter he was most worried about the danger that bears posed. What may sound a little silly now was actually a matter of serious concern, he explains later.

“They told us that we would be going through regions where bears outnumbered humans,” he says. “And some of the time the only place we had to sleep was right there on the roadway itself. You just feel very exposed.”

Halfway into that preparatory period, the project was threatened after one skeptical consultant contacted the motorcycle company that had offered to provide bikes for the trip and told the executives he expected Boorman and McGregor to fail on their journey. The company immediately withdrew its support, but BMW stepped in with its equipment.

At times, the logistics of the project threatened to overwhelm what McGregor and Boorman wanted to be an intimate experience between two friends.

To keep the experience as “pure” as possible, footage of the trip was filmed mainly by the two actors via cameras on their helmets and bikes, plus director of photography Claudio Planta, who traveled with Boorman and McGregor for most of the journey. The trio met with additional crew members at border stops, where they exchanged their used film for fresh stock.

“Claudio really was the person who made this whole thing work as well as it did,” Boorman says.

“He truly was the third cameraman, but he was never intrusive, so Ewan and I really did feel for a lot of the trip that we were alone together on the road.”

“We know this was a once-in-a-lifetime experience,” McGregor adds, “and I’m just totally thrilled that we have this really incredible ‘home movie’ of it.”

John Crook writes for Tribune Media Services.

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‘Long Way Round’

What: Six-part limited series

When: Premieres 10 to 11 p.m. Thursday; continuing weekly in that time slot.

Where: Bravo

Rating: TV-14