NASHVILLE -- Darius Rucker is a fan of Old Crow Medicine Show, but says he didn't really get what was so infectious about the string band's signature hit "Wagon Wheel" at first.

Then he heard the faculty band at his daughter's school play the song and it all started to open up for him.

"I'm sitting there listening to it and I say to myself what I always say to myself, 'I want to cut this song,'" Rucker said. "I say it all the time but I never end up cutting anything. But with this song it was, 'All right, let's try it.' I didn't know how big it was until after I cut it, until after it was a single. I didn't know that every college student south of the Mason-Dixon Line in the last eight years knows this song. I had no idea. I thought it was just another Old Crow song until I recorded it and realized it wasn't just another Old Crow song."

So far, Rucker's version of "Wagon Wheel" is the most successful song of his country career. The cut from his third Nashville-recorded album, "True Believers," out this week, has sold nearly 1.2 million copies and sat atop the country charts for three consecutive weeks earlier this year.

It's another interesting chapter in the history of a song that's slowly working its way toward American classic status. Like "House of the Rising Sun" or "Good Night, Irene," it's now a pop song with a long back story that tantalizingly trickles out before you reach the wellspring.

Ketch Secor of Old Crow Medicine Show first encountered the song when his friend and future bandmate Chris "Critter" Fuqua brought home a Bob Dylan bootleg from a trip to London that contained an outtake from the singer's "Pat Garrett and Billy The Kid" soundtrack sessions called "Rock Me, Mama." It wasn't so much a song as a sketch, crudely recorded featuring most prominently a stomping boot, the candy-coated chorus and a mumbled verse that was hard to make out.

Dylan didn't claim authorship of the song. He cited Arthur Crudup's "Rock Me, Mama," but Crudup said he got the song from Big Bill Broonzy, who recorded it as "Rock Me Baby." Broonzy didn't claim ownership either and the trail dissolves there, lost to history.

A few months after first hearing "Rock Me, Mama," Secor was away from his native Virginia attending school in New Hampshire and feeling homesick for the South. He sat down and wrote a song about hitchhiking his way home full of romantic notions put in his head by the Beat poets and, most of all, Dylan.

"I listened to Bob Dylan and nothing else," Secor said. "Nothin' but Bob for four years. It was like schooling. Every album and every outtake of every album and every live record I could get my hands on and every show I could go see live. I was a teenager who was really turned on to Bob."

The song was an early entry in the group's catalog when it formed a few years later and was officially released twice, on an early EP and on its second album, 2004's "O.C.M.S." The song's popularity grew with each live show as fans enthusiastically sang along with that catchy chorus and with each fan video posted on the Internet. In the-little-engine-that-could style it attained gold status in November 2011, seven years after it became available digitally.

The story gets better. Over the next 13 months the song would go platinum as the band gained more popularity, thanks to years of hard work on the road, championed by Mumford & Sons and Rucker's decision to cover "Wagon Wheel," and has now up to 1.2 million copies sold and counting. Combining sales for Rucker and Old Crow's version, that's nearly 2.5 million copies sold.

"It's like having four aces in your pocket, that song," Secor said.

While the recorded version is rousing, nothing beats the sound of thousands of voices raised during a live concert. The chorus works its way into memory immediately, making it easy for even the newest of fans to join in.

"I find that the number of singers in the chorus makes it all the more exciting," Secor said. "That's what folk music is and this is a folk song. I think the thing that's interesting about 'Wagon Wheel' is that a folk song could be really popular in 2013. Every strike is against it. All the odds are against folk music, particularly one song rising up and having an impact."

The proof of a song's universality is its ability to jump between genres. Already presented in blues and folk versions, Rucker changed it yet again to fit his silky baritone and traditional country and classic rock influences. He invited in the trio Lady Antebellum to provide backing harmony, again changing the song in unexpected ways.

"It's such the perfect country song," Rucker said. "When we were cutting it, all we had (to model it on) was this perfect bluegrass song. I couldn't do it as a bluegrass song. It's just not me. So if we were going to do it, we had to make it a 1950s country song. I'm not shocked at how successful it's been, but I didn't expect it."

As the song itself inspires fans to raise their voices together, it's inspired Rucker and Secor to collaborate. OCMS recently joined Rucker on the Grand Ole Opry, where they got a standing ovation. And Rucker says when it's time to start working on country album No. 4, Secor's the first guy he's calling.

Secor thinks that kind of cross-pollination is an important legacy of the song as well and hopes the powers that be in mainstream country music are paying attention.

"Country music has made it damn near impossible to get a song like 'Wagon Wheel' into the arena," he said. "We're sitting out there on a side stage out in the parking lot somewhere. But this song managed to seep in somehow. As someone who's interested in seeing country music come around and look at its parentage and be a little more respectful to it, I'm really pleased that this song is helping to do that kind of work in Music City."

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Online:

http://dariusrucker.com

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