A Pyrenees blast furnace has vaporised Cadel Evans's hopes of reaching the Tour de France podium in Paris this Sunday.

Weakened by stomach trouble, the defending champion cracked twice on a brutal mountain stage and there was no coming back the second time.

As race leader Brad Wiggins tightened his grip on the yellow jersey, Evans finished the 16th stage of the Tour de France four minutes and 47 seconds behind the British star.

That meant Evans dropped from fourth to seventh on general classification, his deficit to Wiggins ballooning from 3:19 to 8:06.

Realistically, Evans' best overall hope before Wednesday was to stay in touch with third-placed Italian Vincenzo Nibali and then probably take his place with a better time trial on the second-last stage.

But Nibali's Liquigas-Cannondale team forced the pace and then he attacked three times on the final climb to put as much distance as possible between himself and Evans.

Nibali now looks safe in third place, 2:23 behind Wiggins and his Sky teammate Chris Froome. Evans looked disconsolate and tired at the BMC team bus and said his stomach problems had hurt him.

"When you have it two hours before the race there's not a lot you can do," Evans said.

"Obviously that's not my normal level ... pretty much the Tour de France is over for me."

It was a brutal day, with four climbs through the Pyrenees mountains and the temperature reaching well into the 30s.

Frenchman Thomas Voeckler starred, leading the stage over each climb and snaring his fourth stage win.

But Voeckler was no threat to the yellow jersey - the major action happened in Wiggins' group.

With 41km left, on the Col d'Aspin, Evans lost contact with the yellow jersey. BMC teammates dropped back and managed to pace the Australian back to the yellow jersey group by the last climb, the Col de Peyresourde.

But with 19km left, and plenty of climbing to come, Evans again cracked.

Nibali also went on the charge, with Wiggins and Froome able to mark him each time.

The Tour's top three finished the stage together, seven minutes behind Voeckler.

With Thursday's last mountain stage to come and then his time trial specialty on Saturday, Wiggins can smell victory.

"It was another tough one and obviously there weren't many bodies left at the end," Wiggins said.

"It's good to get that one out of the way."

The only good news for BMC was that Evans' American teammate Tejay van Garderen strengthened his hold on the young rider category and is sixth overall, one ahead of the Australian.

BMC intentionally left van Garderen in the Wiggins group when Evans cracked.

At the finish, Evans reached over to his faithful lieutenant George Hincapie, who will retire at the end of this season.

"You have to be optimistic, but also you have to be realistic," Evans said.

"Certainly the retirement present I wanted to give to George Hincapie this year, the hope and wish for that is over."

AAP