Chris Froome cycles to victory in the 32km individual time trial 17th stage of the Tour de France on Wednesday.|Jacky Naegelen/Reuters

Chris Froome may have tightened his grip on the yellow jersey but his capacity to deflect everything the Tour de France throws at him in the coming days, including treacherous weather and technical descents, could be key to overall victory in Paris.

Team Sky leader Froome, who has held the race lead since winning atop Ax-Trois-Domaines on stage eight, claimed his third stage win of the 100th edition with victory in the stage 17 time trial on Wednesday.

Having also won on stage 15 to Mont Ventoux, he has a virtually unassailable lead on Spanish rival Alberto Contador, who finished second at 9 sec adrift to move up to second but is now 4 min, 34 sec off the pace.

With Dutchman Bauke Mollema dropping to fourth place at 6:23, it is now essentially a duel to the finish in Paris on Sunday.

Contador says he will continue to fight, but on Wednesday he said: "Froome is impressive, he is the best both on the climbs and in the time trials. I did what I could."

But while there is no doubt about Froome's superiority, Saxo has promised to test his ability to weather the storm - quite literally - during three tough days in the Alps.

"Tomorrow and the next days we will continue our plan and follow our objective, which is to win Tour de France," said Saxo sporting director Fabrizio Guidi.

Thursday's 18th stage features six climbs, including two ascensions of the Alpe d'Huez. Normally it would hold no fear for Froome, but the heavy rain predicted could play into his rivals' favor.

The descent from the Col de Sarenne, the fifth on Thursday's menu, is technical and would be made even more treacherous in wet conditions.

Froome, who almost crashed into Contador on Tuesday when the Spaniard came off his bike during a fast and technical descent into Gap, said organizers should consider making changes.

"It would be sad not to do the planned parcours (course), it being the 100th Tour de France and with two climbs up to Alpe d'Huez," he said.

"But safety comes first and if it's raining like that I would hope that the organizers would make a decision ... just in terms of the safety of the riders."

Organizers are fully aware of the threat but, despite reports claiming the race could be shortened, no official statement had been made by Wednesday evening.

After the events of Tuesday, Contador and Saxo would arguably be hoping for no changes.

Froome was visibly shaken up by nearly crashing into Contador as the Spaniard raced aggressively on the descent into Gap and later complained his rival had deliberately tried to make him crash.

On Wednesday Saxo team owner Bjarne Riis, the disgraced 1996 winner of the race, said the Briton had a simple solution if he wanted to avoid crashing into his team leader.

"He should use his brakes more if he's afraid on the descents," said Riis.

When confronted with the Dane's statement, Froome said: "Fair enough, I can completely understand that, but all the riders are going to be in the same conditions.

"It is a really dangerous descent and the surface is not in great condition."

During the next three stages, the key to Froome' maiden Tour title may lie more on his, and Sky's, ability to handle quick and treacherous descents and less on his ability to climb.

Despite his considerable advantage, Froome - who has already admitted he has everything to lose - knows the race is far from over.

"Even though I've got quite a good buffer, that's still being challenged every day and these next three days are going to be the hardest of the Tour so far," he said.

"I think it's evident that the Spanish guys are not going to stop racing, neither are the Dutch guys. It's going to be a race all the way to Paris."

Riis said: "We are going to attack everywhere, whether it is going uphill or downhill."