On Wednesday, a hilly time trial is expected to play to Froome’s strengths. But the stage is also likely to feature a fierce battle among the riders trying to reach the podium in Paris. Thursday will provide perhaps the most awaited stage of the Tour: a double ascent of towering Alpe d’Huez.

Between the two climbs, the riders will face a treacherous descent, off the Col de Sarrene along a back road that has not been used in the Tour before. Several riders, including Tony Martin of Omega Pharma-Quick Step, have raised concerns about the safety of the road, which is bumpy and lacks guard rails.

“It is a very dangerous descent,” Froome said Tuesday. “It’s not smooth, that’s for sure. There aren’t any barriers on the corners. If you go over the corner, you will fall down a long way.”

“Like we’ve seen today, this race is far from over,” he added. “One incident, one mechanical, or one crash in the wrong moment, and your Tour can be over.”

Indeed, at this point in the three-week race, when the leader is trying to stay safe while his rivals are trying to pressure him into dangerous mistakes, descents become all the more crucial. Yet, descending remains the forgotten stepchild of bike racing, with far more attention given to climbing, sprinting and time trialing.

To casual observers, riders flying at speeds in excess of 50 m.p.h. downhill may appear to be taking a break after a hard climb. But far from it. With so many dangers to worry about, including gravel, holes, wet spots and unexpectedly sharp turns, the riders must remain intensely focused. A crash would not just cost a rider time; it would probably end his race.

“Descents are tough on the riders,” said Michael Barry, a former Grand Tour rider from Toronto who retired from the sport last year. “It’s not like you can relax and coast. The television doesn’t capture the speed the riders are descending at, how close they are to each other, and how fast they accelerate to catch each other.”