Brian Smith has observed the world's leading cyclists from close quarters this season and while the Scot admits it is hard to look beyond Albert Contador as a likely winner of the Tour de France, he believes the outcome of the 98th edition of the race, which starts today, is no foregone conclusion.

“For me, Contador has to be favourite”, says Smith, who spent almost a decade in professional racing. “But he only finished second in the road race and third in the time trial at the Spanish championships last weekend.”

If that apparent sign of weakness offers some hope for rivals looking to topple the defending champion, Smith, who was part of the Eurosport commentary team when the Saxo Bank rider secured the Giro d’Italia title in May, has more good news.

“The guy looks amazing on the climbs,” he said. “He is head and shoulders above the others. But he is certainly not amazing in the time trials this year and he is beatable.”

That is a positive message for the leading British challenger, Bradley Wiggins. Smith, a previous holder of the British road race title won emphatically by Wiggins last weekend, believes the Englishman will bounce back from last year’s disappointing 24th place to challenge for a top-three finish when the race reaches Paris on July 24.

“I think Brad had a bit of a wake-up call at the Dauphine”, said Smith referring to Wiggins’ overall victory in an event dubbed the “mini Tour” because it covers parts of the Tour de France route and features many of the leading contenders. “He sat too far back in the field on one of the main stages and he was fortunate that it all came back together. That was the difference between winning it and losing it, and he learned from that. He can take time off Contador in the time trials and I think he is in with a shout for a place on the podium.”

While many people have tipped the Schleck brothers, Andy and Frank, as possible challengers for the €450,000 winner’s cheque – from a total prize pot of €3.5m – Smith believes the duo from Luxembourg, racing for Leopard-Trek, are short of their best form. Nevertheless, he expects Andy, last year’s runner-up to secure a top-four finish.

Smith sees Cadel Evans (BMC Racing), who finished second in 2008, as a potential winner. The Australian has shown signs of returning to his best form and has stage race wins in the Tirreno-Adriatico and Tour de Romandie to his credit this season.

A race as gruelling as Le Tour will inevitably throw up some unforeseen outcomes, and Smith sees the Slovenia’s Janez Brajkovic (Radio Shack) and Tejay van Garderen (HTC-High Road) of the United Stated as unheralded challengers. However, it is the potential of the rising star Ben Swift, a team-mate of Wiggins at Sky, that excites the 1984 Olympian.

Smith said: “He could be the surprise package. It’s his first Tour de France and if he can get in a break he could be an outsider for a stage win.”

Smith believes David Millar may have peaked at the Giro d’Italia when the Scot became the first Briton to lead all three Grand Tours and finished with a victory in Milan, but expects the Garmin-Cervelo rider to target one stage victory.

Tipping a winner of the green jersey is a tricky task, and while Smith is reluctant to suggest that Mark Cavendish will enjoy that honour, he believes the Manxman will add to the 15 stage wins he has harvested over the past three editions of the race. “He’s right up there. It’s not easy to win stages but he has a good team,” said Smith. “He has learned a lot over the last couple of years and he is happier in his personal life. He could go out and win five stages.”

With Contador in the field, and doping allegations still hovering around the Spaniard following a failed test last year, the question of drugs will inevitably be raised during the race. An adherent to the “innocent until proven guilty” philosophy, Smith draws parallels with his own former team-mate, Lance Armstrong.

“Contador’s situation is the same as applied to Lance,” he said. “No-one has put down facts. It was a positive test but it could be a result of food contamination. It was a really small trace that would make no difference to his performance. So, by rights Contador should be riding this race. For me the Tour de France is still a great race. I think it would have lost something if he hadn’t been in it. Hopefully we will get through it without any positive tests or rumours.”