Tour de France 2018: Geraint Thomas or Chris Froome - will Team Sky have to choose?

Team Sky's Chris Froome and Geraint Thomas are both in contention for this year's Tour de France title.

But what happens when two team-mates are competing for the lead?

Will the team get behind Froome to help him claim his fourth consecutive title - his fifth overall?

Or will he have battle it out with every other rider to try and snatch the yellow jersey from fellow Briton Thomas, who has a lead of one minute 39 seconds after 16 of the 21 stages?

Who's riding for whom?

Each team consists of eight men. When the team contains an overall favourite, there is usually one leader who goes for the title and seven riders who support him.

Froome is Team Sky's leader but finds himself in second place behind Thomas, who won stage 11 and 12 and appears to be in the best condition of his career.

If it was the other way round and Froome was out in front, Thomas would be expected to do all he could to help out the lead rider.

But with both in contention, those tactics could go out the window.

Former national road race champion Rob Hayles believes the team will allow natural selection to decide for them who to back during the deciding stages.

"These riders are very good friends and have been team-mates for years. They will work together to gain an advantage over the other teams, and then it's up to them to race it out from the road between them," said the BBC Radio 5 live commentator.

But how can team-mates help each other?

"A rider preserves 30-50% of their energy riding in the slipstream behind others, so your team-mates are there to take the brunt of it," said Hayles.

Thomas has been the most consistent rider of the Tour so far but Hayles says the Welshman has not yet been tested at this level.

"Froome has the experience and is the proven one out of the two," he added. "But if I were to predict a winner, it would have to be Thomas - as things stand, anyway."

When team-mates become rivals

Riders used to be incredibly suspicious of their team-mates, according to Hayles.

"You used to hear stories of team-mates refusing to eat near each other due to fear of their food being poisoned or tampered with," he said.

"It doesn't go on nowadays but it certainly used to.

"There were even people who would be so paranoid, they would take their own bike up to their hotel rooms with them for fear their team-mate's mechanics would tamper with them the night before a deciding stage."

Remember Wiggins v Froome?

Team tactics have come into play for Team Sky before on the Tour.

During stage 11 of the 2012 race, Froome was apparently under team orders to support team-mate Bradley Wiggins.

With 4km to go, Froome decided to pick up his pace, leaving behind Wiggins and the rest of the group.

Moments later Froome slowed again, reportedly obeying a series of orders on team radio.

However, Froome once again appeared to write his own rules, sprinting away in the last 300m to distance Wiggins by two seconds.

After the race, he reassured the press that he was not after the title himself and was there to help Wiggins.

It worked - Wiggins went on to become the first Briton to win the yellow jersey.