Defending champion Chris Froome expects a far tougher test at this year's "much more open" Tour de France, saying his rivals were at a higher level.
The three-time winner of the famous race is aiming for a hat-trick of successes in 2017, but faces plenty of competition.
Richie Porte, Nairo Quintana and Alberto Contador are among the other favourites to win the Tour, which begins with an individual time trial in Dusseldorf on Saturday.
Froome, who won last year's Tour by more than four minutes, expects an unpredictable race.
"It's going to be a really tough race for sure," the Team Sky rider said.
"I think the level of my rivals is much higher this year. It's a much more open race, with the course that we have.
"It's impossible to predict."
After the 14-kilometre time trial through Dusseldorf, riders head from Germany to Liege in Belgium in a flat 203.5km second stage.