Their sarcastic personalities and love of fishing, not to mention the fact they're both from Indiana and made their way to the Sprint Cup Series through the USAC Series, make this seem like a perfect match.
But their relationship hasn't always been this good.
In 2006, Stewart was leading at New Hampshire on Lap 91 when Newman, two laps down, refused to pull over and let him pass. The two ultimately got into each other, causing Stewart to crash and fall out of the top 10 that at the time qualified for the championship Chase.
Afterward, Stewart was openly critical of the driver he'll now put into the No. 4 car next season.
"There are guys that are really good at give-and-take and there's guys that aren't," said Stewart, who ultimately failed to make the Chase the year after winning his second title. "Ryan's one of those guys that's not good at the giving part. He's really good at taking.
Newman disagreed, saying he was faster and Stewart should have given him room.
"I guess he's not a giver," he said. "Bottom line is we were in a position to take and rightfully so. We had fresh tires and he was on old tires and he didn't give."
Neither gives a rip about those times now. They're united for a common goal, and that is to win races and ultimately championships for an organization that has never been to Victory Lane.
They're ready to put whatever differences they had on the track aside just as points leader Kyle Busch put his somewhat tumultuous relationship with Stewart aside when he joined Joe Gibbs Racing this season.
"Like everybody said, Tony and I were going to blow up when we were put together," Busch said before practice at Michigan International Speedway. "We've been better working together than facing each other."
And so it will be with Stewart and Newman.
The two will be good for each other, particularly during tough times -- which there are bound to be in turning around an organization that doesn't have a car inside the top 35 in owners' points.
Stewart seemed just as excited for what Newman will bring to him off the track as he will on it.
"Ryan likes to fish. I like to fish," he said. "We both raise baby deer. We have a lot of common interests. This is something that we'll have a lot of fun doing.
"The competition side will probably be rougher with us going fishing, anyway. The first time he gets me in a boat and gets me out about 50 feet and says, 'OK, we're fishing for paychecks today,' I'm swimming back."
Newman laughed. Stewart laughed.
Everybody in the room laughed.
Will they be laughing eight months from now if neither driver has a win or even a top-10? It's too early to say how good this combination will be. It's not ready to challenge Jeff Gordon and Jimmie Johnson at Hendrick Motorsports or Kyle Busch and Denny Hamlin at JGR even though they'll be driving with HMS engines and chassis.
But this tandem has a lot more potential than most of the garage, and Stewart-Haas general manager Joe Custer is almost drooling.
"It's overwhelming in a lot of ways," he said.
Getting Stewart and Newman definitely was a coup for the Haas organization, although it was more of a no-brainer for Stewart since he was given 50 percent of the company.
But getting the right people to surround them will be even bigger.
The thing that impressed me the most about Ryan was he asked all the right questions from day one. We've still never spoke about a dollar and a contract.
-- Tony Stewart
"Those guys are talented drivers," Brian Vickers said. "They're unique personalities. But that doesn't mean they'll be successful. That group is going to need a strong leader to direct that team.
"This sport is about chemistry. It's got to be the whole picture. You can't just drop two drivers in and all of a sudden they're going to win races."
"It's going to take some time to build that organization to where Tony might want to see it in a few years," he said.
Kurt Busch, Newman's teammate at Penske Racing, said from a personality standpoint Newman and Stewart appear to be a good fit.
"Now will it fit from the racing side?" he said. "That's what time will tell."
The good news is top talent from other teams apparently are lining up to join the organization. Chances are there'll be a complete overhaul in personnel before the Daytona 500 in February.
"The flood of personnel that have come over and wanted to join the team since we made the announcement has been huge," Stewart said of his deal with Haas. "With the addition of Ryan coming on board, it's even going to make that list grow larger."
Newman was impressed enough with the possibilities that he left a well-established organization at Penske Racing to join one that has one top-5 since it began in 2002.
He left in part because he felt management at Penske suffered with the retirement of team president Don Miller and in part because he likes the thought of having an owner like Stewart who will be at the track all weekend, every weekend.
"That is extremely important to me to have somebody that understands the driving part of it, the ownership part of it, the teammate part of it, the personnel part of it, which is extremely important now," Newman said. "I still have a lot of respect for Roger, and I look forward to the rest of the season and fulfilling my obligations.
"But I definitely see the true racer and potential future businessman in Tony Stewart."
In Newman, Stewart sees a driver who has the same passion for winning that he does.
"The thing that impressed me the most about Ryan was he asked all the right questions from day one," he said. "We've still never spoke about a dollar and a contract. From day one the questions were all about how are we going to win races, how are we going to win championships, how are we going to get the right people in place to do the job."
And all it took to convince Newman to join him, Stewart joked, was four days of sedation and subliminal messages.
"We're going to have a lot of fun with this," Stewart said. "It's hectic and busy, and as tedious as the schedule keeps getting every year to have somebody like Ryan on board that we know we're going to have fun with, that makes you look forward to going in there and doing the work each day."
David Newton covers NASCAR for ESPN.com. He can be reached at firstname.lastname@example.org.