Couple step out of comfort zone to tour world
They believe this to be the first round-the-world trip in a made-in-China plane.
Zhang explains the reason for choosing such an old plane was not to deliberately create a thrilling effect for the program but rather because it was "the only plane we could afford".
The new season has attracted about 300 million clicks online, and its rating on Douban, China's major film and TV review website, is 9.2 points out of 10.
The couple stopped at 45 stations in more than 23 countries during the trip and recorded their meetings with local people, including a soccer team in Sierra Leone, which comprised youngsters who had lost their legs in the blood-diamond war, and families separated by the wall erected on US-Mexican border.
"We take our stories to different places and bring local people's stories back," says Zhang.
The popularity of the couple's online show means it has also been a hit with sponsors. In a publicity slogan for the new season, the show was labeled as a promotion for made-in-China products.
As a result, there have been concerns that the couple will have to give in to sponsors' demands and will be unable to stick to their original style of travel in the future.
"We often remind ourselves that no matter how far we've gone, don't forget why we set off. We expected that some changes will come after our journey, but we'll keep this program as it is," says Zhang.
He says On the Road would be destroyed if there were detailed scripts designed for them to show products on screen.