Tour de France Tension Simmers on Twitter Last Updated, 8:35 p.m. After Thursday's race through the Alps seemed to signal that the defending champion is on the ropes, the Tour de France is starting to look like a battle between two British riders: Bradley Wiggins, a veteran of track racing from England, and Chris Froome, an emerging star born at altitude in Kenya. What made matters a little awkward near the end of Thursday's slog up the day's last mountain is that the two rivals are also teammates. The men race for Team Sky, a British-based squad ostensibly designed to help pace Mr. Wiggins around France in the yellow jersey of the overall race leader. That pecking order was on clear display late in the race on Thursday, when Mr. Froome, whose main job is to ride just in front of Mr. Wiggins, helping his team leader to conserve energy by shielding him from the wind, suddenly set up an attack on the slopes of the day's final climb to the ski station at La Toussuire. As Mr. Froome pedaled away from the rest of the pack, Mr. Wiggins was left behind, isolated and unable to keep up even with the small group of other contenders for the overall title struggling to respond to the sudden acceleration. Moments later, however, Mr. Froome appeared to get a radio message from his team to slow down and wait for Mr. Wiggins, which he dutifully did, allowing all his rivals for second place to gain time on him in the process. Such is the life of a support rider, even one who might have the legs to defeat his team leader. After the stage, Mr. Froome found himself besieged by questions from journalists who seemed to be encouraging him to try to beat his teammate. Although Mr. Froome knows his place, and is handsomely rewarded for putting his team's ambitions ahead of his own, there were signs after the stage that tension between the two men might be building. Shortly after the race concluded, a note appeared on Twitter from Catherine Wiggins, the cyclist's wife, in which she praised two of his teammates, but not Mr. Froome, for their "genuine, selfless effort and true professionalism." Apparently taking that as a slight, Michelle Cound, a sports photojournalist who dates Mr. Froome, responded: "Typical!" Ms. Cound also wrote that she was "beyond disappointed," presumably that Mr. Froome had not been allowed to race on to the end of the stage. Then she suggested, in an update referencing her partner's nickname, "Froome dog," that his loyalty was a good quality even if it was "being taken advantage of by others." The spat received more attention after another British cyclist, David Millar, who observed on his Twitter feed, "Oh SNAP! Sky have WAG WAR on Twitter," using the London tabloid acronym for the wives and girlfriends of male sports stars. A few hours later, Mr. Wiggins appeared to make an effort to calm the waters with a message on his Twitter account, in which he singled out Mr. Froome. That Thursday's minor altercation took place on Twitter was a reminder that, more than most professional athletes, cyclists appear to spend an inordinate amount of time on the social networking Web site. Perhaps because they spend a lot of time recovering from their exertions on team buses and in hotels, alone with their phones, many of the sport's top riders -- and their families and team support staff -- post frequent updates, bantering with their friends and rivals, and even responding to questions from fans. Just as they are on the road during races, professional cyclists are unusually close to their fans on Twitter. While riders see plenty of messages of support from fans, the online conversation is often dominated by questions about drug use. Given the sport's recent history of problems with performance-enhancing drugs, some of those questions are quite barbed, and it appears that even the leading riders have trouble blocking out the virtual taunts from fans who suspect them of doping. Thursday's intramural skirmish at Team Sky came just days after Mr. Wiggins had responded with a foul-mouthed tirade to a reporter who asked what he would say to cycling fans who suggest on Twitter that his improved performance this year might be explained by doping. "It's easy for them to sit under a pseudonym on Twitter," Mr. Wiggins said, in the one semi-printable section of his answer, "rather than get off their arses in their own lives and apply themselves and work hard at something and achieve something." Although Mr. Wiggins found support for his response from Mr. Froome, and from the leaders of an American team dedicated to drug-free riding, his use of two highly unprintable epithets to refer to skeptics on Twitter offended fans of the sport who use their accounts mainly to press for full transparency from the riders. Responding to Mr. Wiggins, the blogger who writes the Cycling Fans Anonymous Twitter feed, insisted that fans have every right "to ask questions about doping in cycling. The cyclist's attempt to silence critics even led to a wry response on the social network from Floyd Landis, the winner of the 2006 Tour who lost that title after failing a drug test (and now writes under the handle @FakeFloydLandis). The tirade also led several fans to press for an explanation as to why Team Sky, which was founded with a promise to support clean riders, now employs a doctor who worked for more than a decade for Rabobank, a Dutch team that reportedly tolerated systematic doping. As the volume of questions about the doctor intensified online after Mr. Wiggins's rant, Team Sky's director was eventually forced to explain the decision to employ someone associated with the Dutch squad whose leader was forced from the 2007 Tour, while leading it, after it emerged that he had dodged drug tests. Despite retaining that doctor, Sky's director insisted that all of this riders, including Mr. Wiggins, were now riding without the aid of drugs. The fact that Mr. Wiggins was once outspoken about doping, before his transformation from a support rider to a star, seems to have added to the disappointment of fans who want to believe that the spectacle they are watching is real, but have been burned before. As the crusading former cyclist Paul Kimmage observed this week, "He was so outspoken about doping before, and needs to keep doing that. And the press need to be asking questions, too. The greatest indictment of our profession at the moment is the fact that although Wiggins had this rant about Twitter, that is where the pertinent questions are being asked now: on Twitter.