Chris Froome favourite as unpredictable Tour de France begins in Dusseldorf

What promises to be an unpredictable 2017 Tour de France gets under way with a short time trial in Dusseldorf on Saturday.

The 14 kilometre battle against the clock, up and down the banks of the Rhine, is not long enough to create major gaps in the general classification but should give an early indicator of form.

Team Sky's Chris Froome arrives as the favourite as he chases a third straight Tour title and fourth overall, but a slightly unusual parcours for the three weeks ahead means it is less than straightforward.

There are only three summit finishes and relatively few time trial kilometres - precisely the sort of terrain where Froome has gained time in the past.

Froome, who on Friday signed a new three-year contract to remain with Team Sky until 2020, will take heart from the way he stole time on his rivals 12 months ago, attacking on descents and in crosswinds to pick up advantages in unexpected places.

"What happened last year wasn't planned," he said. "I was just racing in the moment and making the right decisions. The race this year is going to be a race that favours more aggressive riders. Certainly I'll be looking for those opportunities and will ride an aggressive race if the opportunity is there."

Team Sky head to the start line still facing questions about the ongoing UK Anti-Doping investigation into allegations of wrong-doing.

Those allegations have been denied time and again, but the team is still under intense scrutiny. While Froome has appeared unruffled, it remains to be seen if it will have an affect once the race is under way.

Certainly, Sky's rivals do not appear shy in coming forward to suggest the team this year is not as strong as in editions past.

At the front of the queue was Froome's friend and former team-mate Richie Porte, now at BMC and seen as the most likely to end Sky's stranglehold on the race.

Given the course, Porte predicted a "free for all" over the next three weeks.

"I would guess the time gaps are not going to be massive," the Tasmanian said. "It's going to be a hard race to control."

Although the time trial will create some separation there may not be a real shape to the general classification until stage five and the finish at La Planche des Belles Filles.

Until then, it is a battle to stay safe and limit any losses, starting with a time trial expected to be contested in wet conditions.

Bury's Simon Yates, the 24-year-old Orica-Scott rider, joked a little bit of Manchester weather could help get his bid to win the young riders' white jersey off to a strong start even though time trialling remains a weakness for him.

"I hope so!" he said. "The time trial sets out a bit of an order. We really see straight out of the gun who's got it and who's not."