One of the most incredible runs in auto racing history centers on a number that means nothing to most people but was unfathomable to the only ones who understood it.
That was the fuel number Andretti Herta Autosport gave Alexander Rossi in last year's Indianapolis 500. It was the miles-per-gallon target (disguised with code) Rossi had to hit over the final 30 laps to have a shot at a career-defining achievement.
It was also, undeniably, crazy.
"It was more than crazy," Rossi said. "It was probably absurd."
Even to the number cruncher who proposed it.
"I was a little skeptical of whether or not it could happen," assistant engineer Nick Heinz said. "But we went for it."
And it worked — well enough, at least.
Rossi ran out of gas before Turn 4 on the final lap but coasted across the finish line to win the 100th running of the famed event, as a rookie, no less.
A career trajectory that had been uncertain three months earlier soared. Rossi became the IndyCar Series' top rookie. He finished 11th in points and earned another year in the series. He'll be a driver to watch when the season opens with today's Grand Prix of St. Petersburg.
All thanks to an absurd number and an epic victory Rossi never thought was possible.
"I went into it with the goal of winning, obviously," Rossi said. "But I was expecting to run out of gas."
Rossi didn't even expect to get to last year's Indy 500.
The California native left for Europe at age 17 to try to make it in Formula One. He did, becoming the third American to drive in the prestigious series over the last quarter century.
But things never progressed beyond Rossi's five Formula One races in 2015. With options drying up in Europe, Rossi went to Indianapolis last February to hear a pitch from team owner Michael Andretti. Rossi wasn't sure about the deal before the meeting but chose a spot in Andretti's No. 98 Honda over sports car opportunities.
"It was a no-brainer," Andretti said.
Even if Rossi admittedly knew nothing about the series, or its cars. Rossi had never even raced on an oval track before; the Indy 500 would be his first.
Just as it takes a rare breed of driver to set aside fear and get every ounce of speed out of a car, it takes a special talent to figure out how to finish faster by driving slower.
"It's a bit of reverse psychology, really," driver Max Chilton said.
And it's a necessary part of the sport, across series.
Drivers who find themselves in the back of the pack try to pit apart from the leaders. Save enough fuel, snag enough caution laps and find enough luck, and maybe you can skip a time-consuming pit stop and get in position to win.
When the gamble fails, defeat is unavoidable. But when it works, triumph becomes possible.
"Nobody says, 'Indy 500 winner because everybody else ran out of gas,' " former 500 champion Tony Kanaan said.
Rossi had a fast car last May, but pit problems put him behind and forced him to begin conserving fuel halfway through the race. With about 30 laps left, the team told him to save another 20 percent.
He had to hit 4.71.
"My whole world revolved around the fuel number for about 20 minutes," Rossi said.
Hitting that number wasn't hard on its own. The challenge comes from everything else.
Competitors zipped by at 200 mph in unusual parts of the track. Because others still needed to pit, Rossi never really knew if the car in his rear-view mirror was passing him for position. And because he couldn't waste any precious fuel, there wasn't much he could do about it anyway.
All of that on a 24-year-old rookie on IndyCar's biggest stage in a car expected to run out of gas on the backstretch of the final lap.
"To save that amount of fuel and go slow and be relaxed about it — there's not many drivers that can do that," driver Carlos Munoz said.
But Rossi did.
When Rossi's tank emptied around Turn 4 — a little after Heinz expected — Munoz was too far back to catch him.
"Holy crap," Heinz thought, "we're going to win this thing."
Rossi eased past the yard of bricks. He drank the celebratory milk. And eventually, once the shock wore off, the unlikeliest Indy 500 champion ever began to think about what comes next.
Rumors swirled about Rossi making another Formula One attempt, but he decided to stick with IndyCar — a potential rising star in a series craving elite American talent.
As successful as Rossi's rookie season was, he has more to accomplish. He entered the series with no knowledge of the cars, or the tracks. He didn't know the first turn at the Grand Prix went right until he showed up here a year ago.
Now Rossi knows the layouts and schedules and set-ups, and he's still riding the wave from last year's historic run at Indy.
"There was a lot of momentum to take forward," Rossi said.
Even if there's no fuel left to help him get there.