VILLARD DE LANS, France, Sept 15 (Reuters) - Primoz Roglic and Tadej Pogacar are bracing themselves for a day of reckoning on the Tour de France as Wednesday's brutal 17th stage could decide who, of the yellow jersey holder and his young challenger, will win the all-Slovenian showdown.

The 30-year-old Roglic leads Pogacar, 21, by 40 seconds going into the physically demanding 170-km trek through the Col de la Madeleine and finishing 2,304 metres above sea level at top of the Col de la Loze, an unforgiving 21.5-km ascent at an average gradient of 7.8%.

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Roglic can rely on the strongest team in the field, Jumbo-Visma, while Pogacar - who lost 1:20 in crosswinds in the opening section of racing - has been the most explosive rider.

"There are some big days to come. Tomorrow is this year’s queen stage. The final climb is the highest point of the route, and its last kilometres are very hard ones, as we have to ride a steep bike path. We’ve recced the climb," said the ice cool Roglic.

Roglic has been riding very conservatively so far, unlike Team UAE Emirates rider Pogacar, who attacks whenever he feels like it.

Whether Pogacar will make Roglic crack on Wednesday or pay for his repeated efforts is the question on everyone's lips.

"Tomorrow ... the finish is ... going to be very very hard," said Pogacar, who like Roglic has checked out the final climb earlier this season.

"The Col de la Madeleine and the Col de la Loze are two tough climbs, especially the last six kilometres of the Col de la Loze.

"It's really brutal. You can gain a few seconds but if you have bad legs you can lose several minutes." (Reporting by Julien Pretot; Editing by Pritha Sarkar)

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