Two months in, they reached Utah, and the trip almost came to an abrupt halt when Mike accidently drove the bike off the road and into a ditch.
"I was talking to him about having a baby over the microphone, and he lost concentration in a moment of pure terror," his wife said.
As days turned into weeks on the road, the Clears had their share of highs and miserable lows: delightful nights of tangoing and horseback riding, mixed with extreme weather changes and low blood sugar levels that took their toll.
And there were of course fights about directions.
"She lost a GPS in Las Vegas. Unbelievable," Mike exclaimed.
"Low moment, low," Alanna agreed.
Their spirits sank even lower when they drove closer to South America, and the region was in the midst of its tropical rain season. Rain would fill all around Alanna as she sat in the sidecar.
"We'd be driving through lightning storms, and we couldn't see anything and nothing dried because it was so wet," she said. "It was really unromantic."
The Clears love was further tested when they reached Peru and met with a man and his six wives.
"[It was] the biggest fight that we had, which actually challenged our core beliefs," Alanna said. "He talked about those women as slaves."
When the man told one of his wives to kiss his feet, and instructed Alanna to do the same to her husband, she refused and created an awkward situation.
"I said, 'I won't,' and he said, 'Well, then you don't love him,'" she said. "I said, 'Well, I'll do it for him if he does it for me first,' and there was a collective intake of breath from all the wives around the table."
Alanna said that afterward she demanded that her husband explain why he hadn't defended her, and cried for days.
Pushing forward, the trip came to a close in February 2010, and the Clears decided they had finally earned the chance to find out whether they had been in love before their adventure. Taking out Fisher's initial brain scans, the two reviewed the results and were excited about what they saw.
Their scans showed that both had been deep in love before their trip began: The romantic love centers of their brains appeared lit up like Christmas trees.
But now that the trip was over, would their brains still flare up in the same way? The second test followed a few days later, when the Clears found themselves back in Fisher's office. The second set of results would shock them both.
Find out what was in the second envelope and watch the Clears' full story tonight on "Secrets of Your Mind" at 10 p.m. ET