Saxo Bank team rider Andy Schleck (R) of Luxembourg climbs the Port de Bales pass followed by Astana team rider Alberto Contador of Spain during the 15th stage of the Tour de France cycling race between Pamiers and Bagneres-de-Luchon July 19, 2010. Contador is the new race leader. [Xinhua/Reuters Photo]

Schleck had accelerated less than 4 kilometers from the top of the major climb of the day, the Port de Bales, but almost immediately lost his chain, forcing him to stop on the side of the road and wait for assistance.

He then had to force his way back through the field as he attempted to catch up with Contador and the other leaders in the overall competition, but was unable to make up enough time.

He finished 39 seconds behind Contador, who now holds the yellow jersey by eight seconds.

Contador said he had not been aware of Schleck's problem until he had gone far past him.

Voeckler finished Monday's 187.5-kilometer (116.5-mile) 15th stage from Pamiers to Bagneres-de-Luchon in 4 hours, 44 minutes, 51 seconds, ahead of Alessandro Ballan of Italy and Aitor Perez of Spain.

Tuesday's 16th stage, the third in the Pyrenees, is one of the toughest of all, taking the riders 199.5 kilometers (124 miles) from Bagneres-de-Luchon to Pau.