Beltway chatterers say Sen. Rob Portman is too boring to help presumptive GOP nominee Mitt Romney win the White House, but there’s one kind of trail on which the Ohio Republican defies conventional wisdom.

“Well, he’s not boring on a bike,” quipped Sen. John Kerry (D-Mass), one of the Senate’s most avid bicyclists.

Kerry practically serves as the chamber’s ambassador of cycling, arranging long rides from his Georgetown home past Mount Vernon and back at otherwise tense moments.

He and Sen. Scott Brown went for a ride after the Massachusetts Republican captured the late Sen. Edward Kennedy’s seat and broke Democrats’ filibuster-proof majority. The pair rode again on the day the Wall Street reform bill passed, with Kerry talking Brown into being the 60th vote to advance the bill.  And they reunited on a 110-mile leg of a charity race in the Bay State that same summer.

The bipartisan bike caucus expanded when Portman and Sen. Mark Warner (D-Va.) joined the group in the middle of the intense and ultimately unfruitful super committee deliberations. And while no one is saying that the bikers are the next “gang of six” seeking to solve the Rubik’s Cube of revenues versus spending cuts, at least there is a small number of Democrats and Republicans talking to each other outside of the Capitol.

The group hasn’t gotten together in a while. Brown is engaged in an entirely different sort of race, trying to defend his seat against Democrat Elizabeth Warren. Portman is deflecting a constant barrage of speculation that he could wind up as Romney’s running mate after successfully helping the former Massachusetts governor win key counties in Ohio’s March primary. There also was the logistical matter of winter.

“We’re planning it. … We’re going out soon, we hope. It’s time to go,” Kerry said when asked when the group would ride next. “It’s a way to get away from the Senate and have a normal relationship and have fun.”

Many of the bike caucus Members express reverence for their colleagues’ cycling skills, even if they diverge in politics. Several aides, who asked for anonymity so they might speak more freely on the matter, conceded they usually decline to ride along because their bosses are pretty good for old guys.

And even if the rides have become more infrequent, observers say the ritual hearkens back to a time when lawmakers went home less frequently and spent more time in Washington, D.C., befriending colleagues with whom they sparred during the day.

“It’s always good to be in a relaxed atmosphere where you can joke and talk about stuff. They’re all good riders. Scott Brown’s a serious rider. He does triathlons. Mark Warner’s a good rider,” Portman said. “I think it is valuable. You tend not to have much time.”

Portman, who has a kayak mounted on a wall in his Russell Senate Office Building suite, said the last time he went for a ride was last Thursday night. The Senator said he often rides at night after work, noting that it was a “big mistake” last Thursday when he went out at night with only “a little flashing light on the back.”

With the bike caucus, it’s always safety first, with serious national issues taking a back seat.

“We just talk about whatever comes up. Just trying to stay safe, first of all,” Brown said. “Hopefully we’ll have some time at some point. I’ve been pretty busy.”

With Brown’s re-election bid, and both national parties funneling serious cash into this cycle’s prize of Massachusetts, the Republican’s interaction with Kerry is even more interesting. Both Kerry and Brown have invested a serious amount of time developing a working relationship, beyond just on two wheels.

Kerry has said he won’t endorse a candidate until after September’s Democratic primary.

It’s a move that, on the surface, respects other Democrats challenging Warren, the frontrunner by far. But from a practical perspective, aides say, it keeps him from fraying ties with Brown, both in the time leading up to the general election and perhaps after if the Republican maintains his seat.

Brown has shown some independence from Republican leaders, breaking with his party on unemployment benefits, on jobs bills and, most notably, on Wall Street reform.

On the May 2010 morning that the sweeping legislation passed, Brown met Kerry at his home at 6 a.m. for a 40-mile bike ride. The two men talked about the bill extensively. Biking was one way the Senators first got to know each other.

“Absolutely,” Kerry said when asked whether the time on the bike trails has helped the two Bay State lawmakers get closer. “I think it’s important to build a relationship with anybody.”

But one real question remains: In a group of lawmakers, uber-competitive by nature, who would win in a good old-fashioned bike race? We may never know.

“I can’t reveal those secrets,” Portman said.