– There was no final straw, no outside influence, no personal trauma that led Tony Stewart to set an expiration date on his NASCAR career.

Instead, the three-time NASCAR champion simply decided enough was enough.

"I think deep down you know when it's time to do something to make a change," Stewart said Wednesday in announcing he will retire from Sprint Cup racing following the 2016 season to wrap up a storied 18-year career.

If there was any doubt Stewart was at peace with his decision, he proved otherwise with a wide smile and his self-deprecating humor during a news conference that lasted nearly an hour at Stewart-Haas Racing.

He called the decision "100 percent" his choice, said the only pressure he received was from those trying to talk him out of it, and he dismissed the idea that his personal struggles the past three years factored into his choice.

Stewart also tried to ward off any sort of retirement tour in 2016 like the one currently going for four-time series champion Jeff Gordon.

Gordon is feted at nearly every track with gifts to commemorate his career, and he visits with reporters almost week to answer questions about this farewell season. Stewart isn't interested in the same treatment.

"Let's establish this right now: I will not be coming to the media center every week to talk about it," he said. "You can save your gifts. I've got enough rocking chairs at home. I'm not really that kind of guy. I'm content to go race and be around the racing community and the racing family and be around our fans. They can just send me a note from the track president and say, 'Hey, thank you,' and that'll be sufficient for me."

Stewart, who deeply loves dirt track racing, isn't getting out of the car for good, though. He said he will still race in some capacity after 2016, and with a soft smile answered, "Maybe. Probably," when asked if he'll get back into a sprint car. Stewart has not raced a sprint car since August 2014, when his car struck and killed a young racer, Kevin Ward Jr., at a dirt track in upstate New York.

His planned departure is not a surprise. Stewart will be 45 next season, he hasn't won a race in over two years and has been privately working on finding a successor for the No. 14 Chevrolet all year.

Clint Bowyer, released from his contract with Michael Waltrip Racing because the team is folding at the end of the season, will replace Stewart in 2017. Bowyer has been looking for a one-year deal while Stewart runs his 18th and final Cup season. SHR also fields cars for reigning series champion Kevin Harvick, Kurt Busch and Danica Patrick.

The past three years have been trying for Stewart. The fatal incident with Ward last year took a toll on him and he still faces a wrongful death suit from Ward's family. He missed the final third of the 2013 season because of a broken leg suffered in a sprint car crash.

He is 25th in the points standings and failed to qualify for the Chase for the Sprint Cup championship for the third consecutive year.

Eddie Gossage, president of Texas Motor Speedway and a close friend of Stewart's, said: "I think he always viewed Cup racing as a job that helped him fulfill his passion for racing on dirt tracks, running world-famous Eldora Speedway or owning the All Star Circuit of Champions Sprint Car Series," Gossage said. "I don't know anybody that loves racing more. He's a sure-fire, first ballot shoo-in for the NASCAR Hall of Fame."