Auto racing has always been a passion of the men in the Ellis family.

Robert Ellis Jr.'s father loved to watch the fast and dangerous sport on TV almost as much as he loved tinkering with cars. His brothers dabbled in drag racing. He has always been fascinated by Formula One -- the European-style racing that uses long, winding courses instead of NASCAR's oval track -- but strictly as a spectator. He never raced, and he lacked his father's knack for auto mechanics.

"I remember one time saying, 'I need to make sure I make enough money so that someone can fix my cars, because it just doesn't look like fun to me,' " Ellis said.

But a year and a half ago, when his 13-year-old son, Bobby -- also a Formula One fan -- began racing go-karts and needed someone to build and tune up his karts, Robert had to develop an interest in auto shop. And like his dad, he discovered that working on cars is fun.

His role as "chief mechanic and bottle washer" elevates him from spectator to participant. Go-karting, Robert and Bobby agree, is a team effort. "The car is half of it, and driving's the other half," Bobby said.

The karts are small and compact -- about 6 feet long and 3 feet wide -- and have no roof. They sit just inches off the ground, so that when they weave around the course, they're practically slithering, albeit at speeds upward of 70 mph. The karts wear down quickly. After every race, Robert and Bobby replace the tires and rebuild the motor and the carburetor. The routine is part safety measure, part performance booster -- restructuring the kart so it's faster and more aerodynamic.

It helps that Bobby is good. Really good. Despite less than two years of driving experience, the Ashburn teenager hits speeds as high as 90 mph. He ranks in the top three of the junior level of the World Karting Association's national road racing series. In May, he beat scores of other area racers, ages 13 to 17, to earn a berth at the Red Bull run-offs in July in Boston, where he'll compete for a spot on the energy drink company's junior team, which grooms young American racers to break into Formula One.

The trip to Boston will be one of 16 road trips the father-son duo will have made this year. They have schlepped their kart as far as New Hampshire, Indiana and Florida.

When they're not traveling, they're at Allsports Grand Prix, an indoor track in Dulles, or plugging away in the family's garage -- long ago cleared of real cars to make room for go-kart parts -- rebuilding the kart so it will be better and faster for the next race.

"Quite frankly, I think that, at 13 going on 14, this is probably one of the few things that would have allowed us to spend as much time together as we do and not kill each other," Robert said.

Spending time together is kind of the point.

"Bobby was going through a phase and getting a little independent," said his mom, Pamela Ellis. He had always watched Formula One on TV with his dad, but go-karting required more commitment and prompted a sort of rebonding between father and son.

"Hanging out with mom at 13 just isn't cool, but hanging out with dad is fine," she said. "It's made them really close."

Plus, she said, "they've really learned to communicate with each other. It's pretty important when Bobby's out there on the kart and he gets off and needs to be able to explain to his dad what's going on with the kart."

That her husband has such open communication with her son -- both on and off the track -- is one reason Pamela tolerates a sport that sends her only child whipping around a race course at breakneck speeds. It scares her to watch, so she closes her eyes for most of the race until Bobby is heading safely across the finish line.

Robert gets nervous, too, but he's quick to point out that although Bobby is a terrific athlete -- before go-karting snapped up his time, he played basketball, baseball and football -- his relatively small size (he's 5-foot-3) makes him vulnerable in any contact sport.

"We used to watch him play full-contact football and just get hammered, and there's probably less risk doing this than there was doing that," Robert said.

Bobby, an eighth-grader at Belmont Ridge Middle School who will be going to Stone Bridge High School in the fall, is fearless.

"The first time I went out I was pretty scared," he said, "but I haven't been scared since. It takes a lot to jump in a kart, but once you do, it's a blast."

Three months ago, at a race in Atlanta, he nearly flipped over when he crashed into a kart that had spun out of control. The collision propelled Bobby's kart into the air, and he came down nose first and skidded several yards before landing right-side up. The accident didn't faze him.

"You can't have a fear of crashing," he said. "If you're gonna jump in the car, you have to take the risk or you won't be fast."

Doesn't that make him a bit of a daredevil?

The conversation paused as father and son exchanged glances, sheepish smiles on their faces. Busted.

"I told him not to use that word," Robert said, laughing. "But yeah, it's true."

That's why he thinks go-karting is such a good outlet for his son.

"He gets out all of that adrenaline stuff, young testosterone stuff. He has to stay focused and disciplined or he's not going to win."

By nature, Bobby is disciplined and focused, qualities that will bolster his talent, according to Francois Duret, a former Grand Prix driver and owner of the Allsports Grand Prix track where Bobby practices. Bobby is determined to do what he can to get better, so that someday he can follow in the tracks of his idol, Formula One world champion Michael Shumaker. He watches races whenever he can, studying the drivers' tactics, decoding their strategies.

"He's a very smart kid, and he always analyzes what he sees," Duret said. "This is why he's becoming good so quickly."

Success can sometimes be bittersweet when parents press their latent dreams onto their children and put unnecessary pressure on them. Not so with Robert and Bobby.

"They work very well," Duret said. "His father is pushing him, but not pressuring him, and there's a world of difference."

Besides, he said, "Bobby has enough drive on his own. He doesn't need pushing, or not much."

He does, however, need a literal push every time he sets down on the track. Robert is the designated jump-starter. He leans over and pushes the kart a few yards until the engine fires. Then he stands back, proud, and watches his creation go.

Bobby Ellis, 13, and his dad, Robert, of Ashburn, complement each other as driver and crew of a winning racing team. "It takes a lot to jump in a kart," Bobby says, "but once you do, it's a blast."