(FORTUNE Magazine) - Yellow has a mixed history in the Tour de France. The overall leader and eventual winner of the grueling, three-week-long, 2,700-mile bike race wears a yellow jersey. Yellow also signifies a seminal event in French product placement: The race's first sponsor in 1903 was a newspaper called L'Auto et Le Velo, or "Car and Bike," and the winner's sunflower-hued jersey and yellow bouquet matched the paper's yellow newsprint. But yellow also harks back to one of the race's less glorious moments: Dante Coccolo's urinary faux pas.

It was a sultry day in 1978, and the Tour's 100 racers were grinding through a 130-mile stage from Bordeaux to Biarritz. Most of the competitors were riding together in the peloton, the picturesque mob of competing teams that glides in formation across the French countryside every July. With little warning, but as sometimes happens during long stages, somebody called for a bathroom break. Many riders from the race's ten different squads pulled to the side of the road and hopped off their bikes to relieve themselves. Those who didn't stop slowed down.

But instead of extending that customary courtesy, French rider Dante Coccolo decided to attack. His goal: sprint while others were taking their respective breaks, thereby putting a large time gap between himself and the group. Perhaps he'd even snatch one of bike racing's most prestigious prizes, a Tour stage win. But Coccolo's gambit backfired: He had breached peloton etiquette. Again.

"He had a habit of attacking on bathroom breaks," says Paul Sherwen, a Tour racer who was in the peloton that day and who is now one of the world's best-known cycling commentators. "He thought it was quite amusing. It's not illegal, but if 20 or 30 guys stop for a break and you go off on an attack, you're going to make 20 or 30 enemies."

Peloton is an old French word for "big ball of yarn" and also, roughly, "platoon." But in a bike race the peloton is the scrum of cyclists (150 or so in the Tour de France) who race together to conserve energy during long stretches of each stage. And even though the polyglot group often boils over with international grudges and nuclear tempers, in Coccolo's case, the peloton had little problem coming up with a solution.

"When it was Coccolo's turn for his own bathroom break and he put his bike down on the grass verge," Sherwen says, "a couple guys slowed down and grabbed the bike. They wheeled it down the road for a kilometer or two and tossed it into a ditch. Everyone in the peloton was very happy about it."

When Coccolo emerged from the woods, his bike was gone. He had to stand by the roadside for about five minutes, spandexed and ostracized, alongside a few sunbaked, beer-sodden fans. His team manager showed up in a sponsor car, put Coccolo on the hood like an ironic hunting trophy, and drove him to retrieve his hijacked equipment. Coccolo finished second to last that year. He would never ride in the Tour again.

Nothing in American sports resembles the bizarre dynamic of the cycling peloton, partly because a stage race is less a sporting event than a commodities exchange on wheels. What appears to be a random mass of bicycles is really an ordered, complex web of shifting alliances, crossed with brutal competition, designed to keep or acquire the market's most valued currency: energy. Amassing it (i.e., letting as little of it as possible drain away) is the only way for a racer to survive the brutal physical strain of a Tour de France, the metabolic equivalent of running 21 marathons in 23 days.

Bikers save energy by riding together in a massive slipstream. Those who save the most energy can "buy" various goods - international glory, TV time, a bright-yellow jersey, attractive French girls. But here's the key: To thrive in the angry little swarm that is the peloton, enemies often have to stick together and make deals with each other. Cooperation across enemy lines is the centerpiece of a winning game plan. It's a weird concept to those accustomed to the zero-sum, us-them finality of the walk-off home run or the Hail Mary touchdown pass. Why play nice with someone who might beat you? Racers in the peloton are not pals; they're enemies without options. John Nash, meet Lance Armstrong.

The hierarchy in the peloton has another parallel: "It's basically a penitentiary," says Bob Roll, a former Tour rider and an anchor for OLN TV. "You've got your walking boss, you've got that sneaky little bastard who was in The Longest Yard, you have the honorable veterans, and then the guys who are just doing time, which is most of them. Nobody wants to be anybody's boy, but sometimes you have no choice."

The peloton can be divided into two main groups. First, there are 20 nine-man squads like Lance Armstrong's Team Discovery and Jan Ullrich's T-Mobile. Those teams fight during a five-hour stage to put their leader in a position to win that day or to win overall. Then there are the tiny, quickly formed and just-as-quickly dissolved "teams" of rivals that bond when race situations dictate. That can happen hundreds of times a day. "You have to have strange allies to get where you want to go in bike racing," says longtime tour commentator Phil Liggett. "You have to make friends of enemies. And just as quickly, enemies of friends."

The reason for the cooperation has its basis in physics: Wind resistance is a huge factor in energy use. According to studies done by Nike during its development of Lance Armstrong's speed suit, a bike racer consumes almost 80% of his energy cutting through the air and only 20% moving his bike. To overcome that resistance, racers employ "drafting" - tucking your front wheel just behind the rear wheel of the man in front of you, thereby gliding in his wind-free slipstream and greatly reducing the amount of energy it takes to ride.

Not surprisingly, there is an etiquette to drafting. Riders who draft too much without volunteering to slice through the wind for others are "wheel suckers." Italian riders say that a wheel sucker is furbo, or "clever," because he has managed to get away with something. However, if the rider gets caught wheel sucking and gets yelled at by members of the peloton, he is called furbo, or "not so clever." Sometimes foreigners don't have a different word for everything.

Pelotons are resource-rich environments for energy traders. With everybody crammed together, the tools for attacks, truces, breaks, sprints, food, and vengeance are all close at hand. Tactical moves can be made quickly to suit the situation. Last year, for example, with about eight miles to go in Stage 10, a strategically vital mountain stage in Courchevel, Team Discovery's Lance Armstrong and CSC's Ivan Basso managed to open up a big gap on the rest of the peloton, including on their mutual rival, one-time Tour winner and German T-Mobile star Jan Ullrich.

Both Armstrong and Basso were suffering, with the stage's hardest climb to come. According to Armstrong's coach Chris Carmichael, Armstrong turned to Basso and made a deal: They'd work together with a Spanish rider named Alejandro Valverde in the small breakaway group they had formed to draft off each other and save energy. Together they would extend the gap over Ullrich, maybe even knocking him so far back in the overall time standings that he'd be out of contention altogether.

The transaction was straightforward: Basso and Armstrong, archrivals, knew they could speed their ascent and cut their energy output while crushing Ullrich. And they also knew that even if Valverde beat both of them and won that stage, which he eventually did, his chances of winning the overall Tour were slim. How could they so easily discount Valverde's prospects? Because the two stars knew their respective teams were much stronger. There was no way Valverde's Illes Balears squad could carry the Spaniard to first place in Paris.

In fact, every team's leader depends on his crew to survive the three-week Tour's changing landscape. The best teams have specialists to help position leaders for a win. There are two or three speed specialists, or rouleurs, who can reel in enemy breaks on the flats by sprinting out together with their leader (who coasts in their slipstream) all the way to the breakaway group; domestiques, who get them all lunch and supplies and can ride protective shotgun on the leader's flank; and finally hill specialists, or grimpeurs, who can draft well into the mountains so that the leader is rested for the last, excruciating stretch to the summit.

Back in the peloton behind Basso, Armstrong, and Valverde, other riders would be striking different deals. Some would arrange to be leading the peloton when they rode through their hometown to bask in brief glory. Others would arrange to have the peloton let them go out on "TV attacks" - pointless but camera-friendly sprints designed to snag sponsorship cash.

Most of this dealmaking happens in the front third of the peloton. That's the high-rent district, or what the French call the tete ("head") of the group. The best teams try to stay up there - it's the best place from which to launch an attack.

A rider has to use his head in the tete, where battles for tiny swaths of territory are fought at speeds of up to 60 mph, knuckle to knuckle, with no margin for error. One rider will tuck his shoulder in front of another, and then another rider will regain the advantage by diving for a corner just before another rider gets there. It can be wild - and dangerous.

Riders who can't hack the stress at the tete get flushed to the peloton's tail, where conditions can be even more dangerous. "It's 'the projects' back there," says former Armstrong teammate and nine-time Tour finisher Frankie Andreu about the injured, spent bikers who tail behind. "The guys who are weaker or less experienced end up in the back, and when you're tired, you lose focus and make mistakes. That's when crashes happen."

With energy conservation such an important consideration, it's in everyone's interest to maintain a smoothly running peloton. The healthier the peloton, the more riders finish - remember, coming in first is only one of many paths to glory. (Just making it to Paris is one of the sport's biggest honors.)

Pelotons are healthiest when the opposing forces in them are free to attack one another. The market needs liquidity, in other words. And in the case of bike racing, liquidity happens when an alpha rider simultaneously reassures everybody that someone is in charge - and scares the crap out of them. For the past seven years the peloton's patron (the Italians say capo) has been Lance Armstrong, whose swagger and bluster were backed up by nearly superhuman performance. But it was his searing, even bizarre act of vengeance in the 2004 Tour that best reflects a true patron's power.

With three days to go before his sixth Tour victory, Armstrong had a commanding four-minute overall cumulative lead over the rest of the peloton. Nobody had a hope of making up the gap and beating him. But at the 32-kilometer mark of the 18th of 21 stages, a little-known rider named Filippo Simeoni left the peloton on an attack. Simeoni was in 114th place and posed zero threat to the man in yellow. Four racers of similarly anonymous stature were out in front, and Simeoni thought he might be able to catch them and even steal a scrap of glory by putting himself in a position to win the stage.

But the moment Simeoni accelerated out from the main peloton, one rider followed on his rear wheel - Armstrong. Within minutes Armstrong and Simeoni were riding with the small breakaway group, which openly asked Armstrong what he was doing there. Why was the man in the yellow jersey, only three days from his record- tying sixth victory, leaving the relative safety of his team and the peloton and risking all just to hang out with ... them?

In a word, etiquette. Armstrong explained (in French and English) as they rode: Simeoni had sinned earlier that year, insinuating to the press that drug use was widespread among professional riders. Forget about whether it was true; Simeoni had violated the first rule of the peloton, which is, Don't badmouth your fellow inmates. So Armstrong had decided to deny Simeoni the glory of a win. If Simeoni refused to abandon his effort to win the Tour's 18th stage, Armstrong would ride with them all the way to the finish. And he would win.

If there was silent contemplation of the offer, it didn't last long. "Get the hell out of here," Spanish rider Juan Antonio Flecha reportedly told Simeoni. And so Simeoni did, coasting back with Armstrong until the peloton caught up. "I was protecting the interests of the peloton," Armstrong explained later. "All Simeoni wants to do is to destroy cycling ... to destroy the sport that pays him. The other riders were very grateful."

Of course, if they weren't, nobody was going to tell Armstrong.

Paul Hochman is the Today Show's tech editor.