Tour de France: Chris Froome and his rivals face make or break weekend of strenuous climbing

Froome was reserved during Wednesday's ascent at La Planche des Belles Filles but cannot risk hesitating again

Chris Froome faces a long and arduous weekend of climbs that may define his Tour (Getty)

Tour de France leader Chris Froome and the rest of the peloton begin a brutally difficult weekend of mountain racing on Saturday, where as Froome’s team-mate Geraint Thomas sees it, the top favourites have no choice but to show their true climbing colours - or risk losing the race.

“We’ll definitely get a very good idea of who’s really going well and above all who’s climbing well,” Thomas, currently lying second overall after his spell in the Tour lead, said on Friday.

Wednesday’s ascent of the six kilometre La Planche des Belles Filles in the Vosges mountains offered a first snapshot of relative climbing form, with Froome taking the lead but unable or unwilling to follow an attack by Italian challenger Fabio Aru.

But on Sunday’s stage, with a trio of Hors Categorie climbs in the Jura - ascents so hard they forcibly remain outside the organisers’ ranking of climbing difficulty - there will be no room for those sorts of doubts. And should one of Froome’s rivals attack, the Briton simply cannot risk hesitating like on Wednesday.

“Sunday’s a big, big day, with three really tough, steep climbs, for sure it’ll be one of the toughest of the whole race,” reflects Thomas.

One of Froome’s key rivals, double Tour winner Alberto Contador, is even more categorical: “It’s by far the single hardest day of the 2017 Tour. That’s 110 percent certain.”

On Saturday, the peloton plunge into the little-used Jura Massif range with a 12 kilometre ascent of the Montée de la Combe climb before a final ride along high mountain ridge roads at Station des Rousses.

“It’s a tough little finish, you’ll have be really on it, vigilant,” Thomas reflected. “For sure stuff can still happen”.

“I’m not sure if it’ll be a massive battle, the day after it is even tougher, but there’ll be guys making opportunistic little moves.”

“The weather could be a big factor,” warns Jim Ochowicz, the BMC manager for Richie Porte, considered Froome’s top rival, with thunderstorms forecast for the weekend..

Back in 2010, Thomas was also lying second overall when the Tour last tackled the Station des Rousses ascent, which - he admitted with a grin - “I didn’t even know was the same one that we’ll be going up tomorrow.”

Kittel won stage seven in a tight finish (Getty)

However, seven years ago, the Welshman faded badly on the climb, dropping to 31st. Fast forward to 2017 and even though he says his battle for the overall is currently on hold, Thomas is hoping for a better result.

“I want to improve on the last few years, I want to be in the thick of the action with Froomey and that would mean I’d keep my position or stay up there which’d be a nice bonus.”

Friday’s final sprint stage before the mountains saw Germany’s Marcel Kittel take a third victory in less than a week, albeit by a desperately narrow margin.

Kittel crossed the line less than a tyre’s width ahead of Norway’s Edvald Boasson Hagen, and had to wait several minutes before race judges finally confirmed the Quick Step Floor sprinter had triumphed.

“I had no idea how close the gap was between, just that it was really close,” Kittel said afterwards, “I didn’t even know if I had won."