Gap, France ? Through the picturesque countryside and the strenuous mountain climbs, suspicion rides along with the cyclists at the Tour de France.

Despite the largest anti-doping sweep in years on the eve of the fabled race’s start, there are those who still believe the sport is tainted and at least some of its athletes are cheaters.

“It’s not because there was a big kick to their ant hill that we can let ourselves think it’s finished and that everything has been solved,” said Jerome Pineau, a French rider with the Bouygues Telecom team.

The house-cleaning right before the July 1 start removed some of the top favorites from the first Tour of the post-Lance Armstrong era. But some experts don’t believe the recent doping expulsions will remedy the sport’s doping culture revolving around suspect doctors, unscrupulous team coaches and riders hoping for an extra edge.

And if there’s any time when riders may be tempted to rely on blood doping to boost performance, some experts say, it’s now – as the Tour heads into the final mountain stages with several cyclists still in contention for the famed yellow jersey.

The practice of blood doping consists of an athlete having blood drawn weeks or months before a competition and then passed through a centrifuge to separate the oxygen-transporting red cells. The red-cell-rich blood, put back in through transfusion, can aid tired muscles, providing an extra boost to riders.

The pack rides down the Perty Pass during Sunday's 14th stage of the Tour de France. Despite the removal of a number of riders due to doping allegations before the start of this year's race, there's still rampant speculation this year's tour isn't clean.

The question is how to step up the fight against doping.

Scottish rider David Millar, back at the Tour this year following a two-year doping ban, favors an amnesty for cyclists who come clean. The German T-Mobile team, after the scandal broke, told its riders to avoid seeing trainers or doctors whose reputations have been called into question.

Armstrong used to boast that he was the world’s most tested athlete. And cycling’s rulebook is already among the strictest in pro sports when it comes to drugs.

All cyclists are subject to unannounced drug tests throughout the year and must tell the sport’s authorities where they are at all times – often by fax or via the Internet.

“It’s definitely a pain, because sometimes I can’t tell my mother or my wife where I’m going to be in a week,” said George Hincapie, an American on the Discovery Channel team. “I mean, right now I don’t really know where I’m going to go after the Tour.

“It’s hard to keep up, but it’s important.”

Patrick McQuaid, the head of cycling’s governing body UCI, says no other sport ousts competitors from its events when their names turn up in doping investigations – even before their guilt is proven.

That’s just what happened to nine riders – including 1997 Tour winner Jan Ullrich and Ivan Basso, who won the Giro d’Italia in May – after their names emerged in a probe centering on a Spanish doctor.

The doctor, Eufemiano Fuentes, was arrested in May after Spanish police seized drugs and frozen blood at a Madrid clinic – samples thought to have been readied for blood doping. He has denied any wrongdoing.

“I’m sure there are still other Dr. Fuenteses in the world,” Pineau said. “One store has been closed, but others have been opened.”