It takes less than a minute after Tim Duncan pulls up to the entrance of his car customization business in San Antonio, BlackJack Speed Shop, to realize that this isn't the same mild-mannered Tim Duncan in a Spurs uniform.

Stepping out of his blue Porsche 911 Turbo with gold-finished Pur Wheels—one of his nine customized cars—Duncan opens the front door wearing sunglasses, army cargo shorts and a T-shirt with the ThunderCats logo of the animated TV series. He greets his BlackJack business partner and friend for 18 years, Jason Pena, with a special handshake, only reserved for the two of them. They give each other three slaps with their right hand, a creative touch you wouldn't see from the no-nonsense basketball version of Duncan.

Then he grabs a yellow-canned Red Bull in a mini-fridge by the front desk and leads two people—his older brother, Scott, an Emmy award-winning filmmaker and photographer, who rode with Duncan to the shop, and a writer—upstairs into BlackJack's main office. He leans back in a reclining chair at the desk and sips his drink, then turns around and jokingly knocks on the huge glass window overlooking the car manufacturing area to get his staff's attention below.

Duncan is the boss in this uniquely fun world for The Big Fundamental, far removed from his structured and subdued persona in the NBA, avoiding the public eye with no social media and few appearances. The 39-year-old likes discipline and concentrated effort in hoops and training, which includes Muay Thai, kickboxing and swimming. He even cooks for himself, usually grilling ribs, steak and chicken, without the use of a personal chef as many superstars have. Basketball to Duncan is his job with no fanfare.

"We have an unspoken family tradition of just get it done, work hard," says Scott, who has worked for NBA Entertainment and captured his brother after his different championships, in addition to traveling the world shooting documentaries and other projects. "A lot of eyes are on him in basketball, and he knows he's got to really get the job done."

Duncan also hardly travels in the summer because he feels he already does so much during the season. His girlfriend, Vanessa, and two kids—son, Draven, and daughter, Sidney—are his focus. About three trips are good enough for Duncan: visiting his alma mater Wake Forest and to see his sisters in the area, Cheryl and Tricia, heading back home to St. Croix and traveling to Puerto Rico—tropical places he enjoys for the ocean, fishing, surfing and body boarding. He was going to try kite surfing in St. Croix this summer, but when he was told the training session would take several hours, he says, laughing, "I don't have four to five hours to waste."

Where Duncan really lets loose is in the hot-rod car culture.

"This is just a different world, and I think that's the fun part about it because I play with control and precision on the court, but out there it's different playing with my cars," he says. "I'm not really a flashy guy anywhere else—I don't dress flashy or anything else—but I like to keep my cars nice and I like to customize them. I can do things a little flashier and a little faster, and with a little bit more thought. This is kind of the release part of basketball."

Scott sees his brother's car escape connected to their island background, and, indeed, Duncan enjoys San Antonio for its similar relaxed pace and vibe.

"It's yin and yang. He has a balance going on between basketball and this car element," Scott says. "Off the court, he has dry humor, jokes and pranks. BlackJack is really almost like in our young early days, just vibing out on the island or playing on the beach or something. Really, there's no stress, it feels really good. And I think Timmy's style comes through here as well. He's a smart businessman while enjoying his success. When he's here, he's got that feeling of 'Aaah'—a little breath, extra air, a little island breeze coming through kind of thing."

The relaxed feel extends to Scott—with his long dreadlocks—but also to Duncan's right-hand men, Pena and BlackJack's manager Glen Smith, who have funky facial hair, multiple tattoos and dress low-key, wearing cargo shorts and creative T-shirts like their 6'11" friend. On this day in August, Pena's shirt reads "Bangin' Gears, Hurtin' Ears." Also, Pena has invited his close friend from Arizona, popular tattoo artist Chris Escobedo, to come to the shop and give the three of them, including Duncan, each tattoos. Duncan describes his tattoo as a "car part yin yang, mechanical meets spiritual."

"We've got some personalities. It's a fun group," he says. "It's work and everybody's pushing each other and they're trying to get their job done, but we're just having fun."

Even while I'm talking to Duncan in his office, at one point Pena and Smith walk in with Escobedo to check out his tattoo designs on a computer. After they open the door, Duncan greets his friends as "legends" and loosens the atmosphere of the interview.   

"You're good, man," Duncan says to his crew, making it clear they can stay and won't interrupt things. "We're just talking bulls--t. We're talking all about you," demonstrating his dry humor.

Later, when Duncan starts describing how he met Pena years ago, his close friend interjects, "You were much younger."

"I was much younger," Duncan says.

"You're more handsome now," Pena says.

"I was gonna say. I've gotten better looking over the years," Duncan says.

"You're like fine wine," Pena says.

As Scott points out later, "They're all super happy to work together."

And together, they've built an institution in San Antonio—even attracting customers from out of state—all stemming from Duncan's car passion that started in college.

Revving Up

Duncan didn't get his driver's license until his sophomore year at Wake Forest. Growing up in St. Croix, he says, "I just never had anywhere to go or anywhere to be, and I had friends that drove. It wasn't a stress for me."

It wasn't until Duncan tested out his college friend's Mitsubishi 3000GT that he got hooked.

"That was a fast f--kin' car for the first car to really drive, and it was stick," he says. "It was fun for me, and I've always enjoyed that part of it. Nowadays everything is going away from stick, and I hate that part of it. I enjoy learning driving on manual, and that was a hell of a first car just to be able to fool around in. I didn't have my first car until after the end of my senior year. I got a Yukon Sport."

After Duncan was drafted by the Spurs as the top pick in 1997, his All-Star teammate Sean Elliott took his sports car interest to another level. Elliott would drive Duncan around in his BMW M5 and teach him about high-end cars. Elliott also introduced Duncan to Pena, who's four years younger and was working at a different car shop at the time. Then, about two years into his NBA career, Duncan bought a Porsche 911 Turbo and customized it with new wheels.

"As Tim got comfortable, he started metamorphosing into the car guy," Pena says. "He's well-rounded in respects to the automotive industry and selection of cars per se—big trucks or Mercedes or exotics, like a Nissan GT-R and stuff like that. He's got a good grasp of what and why he's buying the car when he buys something. It fits a specific need."

Duncan states simply, "If I have my kids, I drive something with four doors. If I don't have my kids, I can drive whatever I want."

He now has nine cars, ranging from a 1949 and a 1950 Mercury (his dream cars) to an Audi R8 to a newer GMC Yukon, with a six-inch lift and 22x12 tires. "It's a pretty progressive lift kit and wheels and tires package on that thing," Pena says.

Pena adds about his friend's collection, "He's not ever been the one that needed to have the flashy Ferraris to fulfill some kind of status quo, which is another thing that I respect greatly about him, because obviously he can afford whatever he wants."

Duncan's GT-R was actually featured last year at SEMA, arguably the biggest motor show in the country. The car was nicknamed "Gaijin" (Japanese for "foreigner") because it had rare Japanese parts. The car, sporting the license plate 2L8NOW for "Too late now," can max out at 167 mph in a half-mile distance.

All of Duncan's classic cars feature the same exterior but have chassis upgrades done by BlackJack's crew, including model engines and transmission. In addition to friends' influences, his second-biggest inspiration for old-school cars comes from movies, notably The Transporter, Gone in Sixty Seconds and The Fast and the Furious.

"Like every other car guy, I've watched The Fast and the Furious and I want to go out and race and drift, and all the crazy stuff," says Duncan, who would love to witness a car chase scene on a movie set one day. "Another one of my favorites is Cobra. That's where I got my love for the Merc, where he had the one that had the license plate that said 'AWSOM 50.'"

So what is it like to drive with Duncan, who has done some closed-course racing? Also an amusing time.

"I'm more of a comedy guy," he says. "I just scan all the comedy channels on Sirius. I like to sit there and be amused. But if I'm with somebody, they're the DJ. If I'm with my kids, they're the DJ. They tell me what they want."

Shifting into High Gear

When the NBA lockout started in the summer of 2011, Duncan knew he had a "crap load of time." That's when he wanted to act on a vision he had from driving every day past the Automotive AC shop about 15 miles northwest of downtown San Antonio on the way to the Spurs' practice center.

"My practice facility was like a mile away, so driving by here all the time I swear that I said a hundred times, 'That would be a cool building right there to have if that ever came available,'" he says. "So [the owner of Automotive AC and I] were talking and he's like, 'The building's available.' I was like, 'Absolutely, [I'll take it].'"

Duncan hired Pena to run the shop, and together they came up with the BlackJack name, representing the future Hall of Famer's No. 21 jersey number. Their company's niche would be car customization for speed and performance, with some restoration projects. "We have the motto, 'I just want to go fast,'" Pena says.

They knocked down Automotive AC's entry walls to keep the entrance spacious and friendly, like being back in Duncan's native islands. Inside, customers can hang out in a lounge area with a couch and refreshments or roam around exploring different tires and car appliances while mingling with some of the staff members.

"I want people to walk in there and feel at home and sit down and just be a car community," Duncan says. "People enjoy it. I see guys who are regulars here come in and just chill and feel relaxed enough that they can just hang out with us. Sometimes I sit behind the counter and just sit with [my colleagues] for hours and just mess around with them. That's the kind of vibe I want."

Around town, Duncan says "the word is out" that he's the owner of BlackJack. But he still gets some expressions of surprise from the occasional fan: "I didn't see you driving that. That doesn't seem like it fits your personality."

While he's not around the shop much during the season, he's there almost weekly during the summer in the afternoons after his morning workouts. His involvement is mostly tied to the staff's expansion—there are now 20 employees—and the day-to-day business operations. Sometimes he'll lend insight on a project, but don't expect to see him working under a car.

"He's gotten dirty a couple of times. He's done some welding and other stuff," Pena says. "He's not afraid to mix it up, but we try not to let him get too involved with stuff. We need to just make sure he doesn't get hurt. That's the only thing we're worried about."

On the Spurs' side, they've expressed no concerns and have even offered to help promote the shop, but Duncan doesn't want it to just be about him.

"I didn't name it 21's Car Place," says Duncan, who was named this summer by his fellow NBA peers as the Twyman-Stokes Teammate of the Year, recognizing his leadership, selfless play and being a role model. "I want to have it stand on its own, one, and not be driven just by me."

Amid the backdrop of Texas' big truck culture, the shop has done well enough to open a second branch across town, heading toward Austin. BlackJack's appeal also comes from many of Duncan's current and former teammates who are clients.

Currently, the shop is working on LaMarcus Aldridge's next car, a 1968 Chevrolet Chevelle, which will resemble Duncan's classic creations (same exterior, new chassis). Aldridge is the latest Spur to work with BlackJack, joining the likes of Boris Diaw, Manu Ginobili, Kawhi Leonard, Patty Mills, David Robinson and even GM R.C. Buford.

As for Gregg Popovich?

"We've done tires for Pop. That's about all we're allowed to do," says Duncan, laughing.

Duncan himself has become so well-versed in car mechanics that he can break down an entire car's parts, which he did during a tour of the manufacturing area on this particular day with hip-hop music blasting throughout. He knew each car being worked on—none of them his—and its development process.

"Immense," says Pena, referring to Duncan's car knowledge evolution. "He's so far into it now with us it's ridiculous. He's into drag racing. He's fully submerged in the sport."

Scott is not surprised by Duncan's attention to car details, as he likens his craftsmanship to how he approaches adventure video games.

"He's just a great master of that kind of puzzle piece putting together," Scott says. "He kicks my butt at video games really bad. He likes going to different worlds. Adventure games, Call of Duty, Batman. He's really great, super in-depth."

Racing Ahead

Duncan plans to make BlackJack a full-time priority after his NBA career, with the potential to open a third location in Austin.

"I plan on keeping busy doing this once I'm done playing," he says. "I hope once I have more time, I'll invest more time in here and be around more, and hopefully these guys get sick of me," adding in a hint of sarcasm, with his colleagues standing around him.

While Duncan continues to rev up his many engines, the Spurs have done the same this offseason with arguably their best free agency ever, re-signing several of their core players, including Duncan, and bringing in Aldridge and David West.

"Wow, it's unbelievable," Duncan says. "I would not have imagined it would turn out this way. We've got a bunch of very unselfish guys and guys that know how to play the game, and I think LA and D-West and all those guys kind of fit into that category, so it's not going to be reinventing the wheel. We're going to keep our system the same as we have over the years and plug in new parts and see how it works."

In assessing how he'll mesh with Aldridge, Duncan says, "I'm not worried about him benefiting my game; I'm going to worry about me benefiting his. I'm going to let him do his thing and just see where I can fit in and help. I'm going to ride his coattails and I'm going to push him."

As Duncan reflects on his legacy, he notes that his biggest defining moments are the ones "ending in trophies" and credits Popovich for managing his minutes well every season to play as long as he has. With Duncan turning 40 next April, that timing could mean everything: motivation to continue playing or celebrate retirement.

"I'm going to avoid thinking about [my age]. I've been getting slower, but I still think I'm getting a little better," he says, laughing. "I've been blessed that I've been playing for this long and have been healthy and part of winning teams. There's not really much more to ask for."

There is an incredible ending to Duncan's basketball story approaching, but whenever that time comes, he'll still remain the centerpiece in San Antonio. It will just be in another type of paint: his car shop.

"I'll take full and total credit for being the glue guy," he says, with a smile.

Jared Zwerling covers the NBA for Bleacher Report. Follow him on Twitter and Instagram.