The 2014 Tour de France gets under way this weekend. Ahead of the race we look at the leading contenders to claim the coveted yellow jersey. Source: PA Wire/Press Association ImagesChris Froome (Team Sky)The reigning champion has the best team, can time trial with the best of them and – unlike arch-rival Bradley Wiggins – actually looks threatening going uphill. At last year’s Tour de France, Froome was barely challenged after taking the yellow jersey on stage eight, losing time on only three stages.The Kenyan-born Briton won five general classification (GC) titles in 2013 and has defended his titles at the Tour of Oman and Tour de Romandie this year – although he looked less impressive against Alberto Contador at both the Volta a Catalunya (sixth overall) and the Criterium du Dauphine (12th). But while cracks may be appearing, Froome’s power and the consistency of Team Sky ensures the 29-year-old remains the man to beat.Alberto Contador (Tinkoff-Saxo)The Spaniard made his return to the Tour de France last year after missing the 2012 edition due to a doping ban. Contador finished fourth, over six minutes behind Froome, after falling off the pace on the penultimate stage up Mont Semnoz, which allowed Nairo Quintana and Joaquim Rodriguez to claim second and third, respectively. The Tinkoff-Saxo rider failed to win a GC title in 2013 but has already triumphed at the Tirreno-Adriatico and Tour of the Basque Country this year, while he finished second ahead of Froome at both the Volta a Catalunya and the Dauphine. Contador’s ability to accelerate remains one of the most dangerous weapons in world cycling and, as a two-time Tour champion, he will be one to watch throughout July. Source: Lionel CironneauAndrew Talansky (Garmin-Sharp)Talansky’s smash-and-grab at the Dauphine has catapulted the American into consideration for the Tour de France. The Dauphine is the traditional form guide for Le Tour with nine cyclists having won both races in the same year, including Eddy Merckx (1971), Miguel Indurain (1995) and the past two champions – Wiggins (2012) and Froome (2013). Talansky got into a breakaway on the last stage of the Dauphine with team-mate Ryder Hesjedal and Contador, who was wearing the leader’s yellow jersey, left his chase too late on the climb to Courchevel. Talansky finished fourth on the stage but crossed the line over a minute ahead of Contador to clinch the yellow jersey. It was the 25-year-old’s first GC victory on the UCI World Tour and although it seems unlikely he will be able to replicate that result in the Tour de France, Dauphine form cannot be underestimated. Source: SirottiAlejandro Valverde (Movistar)With Nairo Quintana having raced the Giro d’Italia this year instead of Le Tour, Valverde will lead Movistar at the 2014 Tour de France. The 34-year-old’s best days may be behind him – his best finish at the French grand tour was fifth in 2007 – but he still has the ability in the mountains to be a threat. Last year, Valverde finished over 15 minutes behind Froome but he has claimed podium finishes at the Vuelta in the past two years. The Spaniard would need some luck to win Le Tour but he remains one of the few who could. It would also be a huge statement from Valverde to his critics as his career starts to wind down, as he has been regularly criticised for failing to fulfil his potential. Source: SirottiRui Costa (Lampre-Merida)The Portuguese left Movistar at the end of last year to lead a team and he will get his first chance at a grand tour, when Le Tour begins in Leeds on July 5. Costa has claimed three podium finishes on the World Tour this year, including his third straight GC victory at the Tour de Suisse at the end of June. The reigning world road race champion has also finished second at the Paris-Nice and third at the Tour de Romandie this year. A genuine climber, Costa won two stages at the Tour de France last year and one in 2011, but having never finished higher than 18th at Le Tour, he would have to improve dramatically to be a serious GC contender, while the support the 27-year-old is set to receive from Lampre-Merida will also cast doubt on his credentials.Nadal loses to 19-year-old Kyrgios at WimbledonWeeping Serena in Wimbledon health scare Vincenzo Nibali (Astana)Having claimed his maiden podium finish at Le Tour in 2012 – behind Wiggins and Froome – Nibali bypassed the world’s most-famous cycling race last year to focus on the Giro d’Italia, which he won by almost five minutes. The Italian also has a GC victory at the Vuelta a Espana to his name (in 2010), so if he was to win the Tour de France, he would become just the sixth cyclist to win all three grand tours. With six podium finishes across the grand tours of France, Italy and Spain, Nibali has genuine GC ability but his form this year has been mediocre. The 29-year-old finished fifth at the Tour de Romandie and seventh at the Dauphine but Astana coach Paolo Slongo has claimed Nibali is aiming to peak at the Tour de France.