A local businessman and his two brothers are hitting the road for a nearly 4,000-mile journey across the country. On bicycle. And for Bobby Jenkins, it's personal.

While all three are riding for charity to fundraise for causes they believe in, Jenkins is riding to honor the life of his late grandchild who suddenly and mysteriously died three years ago.

For months, Jenkins has left work, pulled on his biking gear and put mile after mile on the road.

"A lot of what I do is to ride rural from here," Jenkins said.

He's got the lightweight bike. Comfort matters when you're on the road for a long, long time. He was gearing up for the ride of his life.

"Seventy miles in a day is one thing -- 70 miles in two days," he said. "Seventy miles every single day ... that is where it does become a little bit of a grind."

And that 70-mile routine will continue -- every day -- for 3,500 miles.

Oh, and did we mention he's 58?

"I think people do think, 'Man at your age, 3,500 miles is a long way.' But I think they know where my heart is," Jenkins said.

Turns out he's right. His wife and daughter may give him a hard time, but they agree.

"It was just, for me, an overwhelming sense of love," said Jessica Jenkins, Bobby's daughter.

That's because Jenkins is riding this journey for a purpose very dear to their entire family.

Moss Jenkins, was a happy, healthy, thriving almost 15-months-old boy. One day, Moss, the first grandson in the family, was laid down for a nap.

"When I checked on him, I found him unresponsive during his morning nap," Jessica said.

"She started CPR right away," Bobby said. "My wife called EMS."

"After about 30 hours on life support, he then passed away. This was about three years ago," Jessica said.

In the midst of this family's worst moment, even more pain came their way.

"There wasn't any -- any cause that pointed to his death," Jan, Moss' grandmother, said. "And it's the same story with every family that we've met."

Doctors looked at the autopsy and, for the cause of death, could only say: "Unknown."

"I think when you have a sudden unexplained death, I mean we just can't accept that," Jan said.

The family couldn't accept that answer, and thankfully, didn't have to. A group in New York reached out with the first possible answer: SUDC, or Sudden Unexplained Death of a Child.

You may be familiar with SIDS -- Sudden Infant Death Syndrome -- but SUDC is completely different. It's diagnosed in children ages 1 to 17. SUDC does not explain what happened -- it's more of classification of any unexplained death that researchers are trying to determine.

Knowing researchers are looking into SUDC gives the Jenkins purpose.

"We've got to find answers as to what it is," Bobby said. "What causes it? What are there symptoms? What's it related to."

"We've got to find answers, and we've got a little angel on our shoulder helping us along," Jan said.

With his family at home supporting him, and the memory of his grandson pushing him through every mile, Bobby is riding from coast to coast.

To raise funds and awareness and to make sure no one else ever loses their Moss.

"People know my heart and my passion for my grandchildren and for Moss," Bobby said. "Every peddle along the way, I'm gonna be thinking about Moss."

We are keeping up with the Jenkins brothers on their journey, and you can too.

GO HERE for an interactive map of their journey.

They start Tuesday in Seattle and will be posting updates on their website, on Facebook, Twitter and Instagram until they hit New York.