STATION DES ROUSSES, France (Reuters) - If one day on the Tour de France is going to sort the men from the boys it will be Sunday when an already worn-out peloton embarks on a punishing trek in the Jura mountains.
The 181.5-km ninth stage from Nantua to Chambery features 4,700 metres of climbing with three out-of-category climbs, with gradients much steeper than the Tour usually includes.
After the final climb, the riders will need to stay alert as the descent from the Mont du Chat (8.7km at 10.3 percent) is among the most dangerous in the area.
To top it all, possible thunderstorms are forecast.
"It's a fast, tricky descent but, in my opinion, it's more about the climbs tomorrow, that climb (to the Mont du Chat) is savage," Britain's race leader Chris Froome said.
"We could see some really big differences. I expect the GC (general classification) to be blown to pieces."
Before the last climb to the Mont du Chat, the riders, who have been suffering from the heat and endured a hectic hilly eighth stage on Saturday, will go up the Col de la Biche (10.5km at nine pct) and Col du Grand Colombier (8.5km at 9.9 pct).
Froome leads Sky team mate and compatriot Geraint Thomas by 12 seconds and Italian Fabio Aru (Astana) by 14. The top contenders are all within a minute of Froome, but the time gaps should be much bigger on Sunday night.
And by then some will already have lost the Tour.
"Those who want to be on the podium in Paris must be in the top three in the GC on Sunday night after a very hard, very selective stage," Nairo Quintana's team manager at Movistar, Eusebio Unzue, told Reuters.
"It was a very hot first week, with long stages. the conditions are hard."
Froome's outfit have had a relatively smooth build-up to the much-feared stage and the Briton will hope that his team mates will be in control as attacks are likely to come from all sides.
Aru, who won the first summit finish at La Planche des Belles Filles, should be the main threat for Froome, but twice champion Alberto Contador, Quintana, in-form Australian Richie Porte and last year's runner-up Romain Bardet are all aggressive riders and cannot be discarded.
"The strongest will win," Bahrain-Merida sports director Philippe Mauduit, who managed Contador in 2014, told Reuters.
"Maybe a team will invent something unexpected. There will be a clear hierarchy between the top favourites.
"The one who will lose more than 15 seconds will probably not win the Tour."
According to Mauduit, Contador could be a real danger despite his ageing legs.
"He's less sharp than he was but he has had no troubles so far. Not a crash, not a mechanical problem, and he had not been spared from bad luck for a very long time," the Frenchman said.
"He's a force to be reckoned with. Until they sweep him aside for good, he'll be there for the win, it's sure."
Reporting by Julien Pretot; Editing by Ken Ferris