With Chris Froome absent from the race following a serious crash during a recon at the Dauphine in June, Thomas and Bernal have taken joint leadership for the 2019 Tour. Following Wednesday's stage, both Ineos riders are handily placed, around 40 seconds down on yellow jersey Julian Alaphilippe, of Deceuninck - Quick-Step.
Defending champion Thomas entered the race with questions around his form, a contrast to young pretender Bernal, who won Paris-Nice and the Tour de Suisse, as well as finishing on the podium in the Volta a Catalunya, in the build-up to the Tour. Thomas also suffered a crash on the closing kms of Stage 1 but has bounced back well.
Speaking on the first of four Tour de France episodes of The Bradley Wiggins Show podcast, Wiggins - who has been following the peloton as a motorbike reporter - said Thursday's Stage 6 would be the first stern test of Thomas' credentials - although he is backing him to hold his own against Bernal.
"I'm more keen to see how Geraint is going to step up really," he said in conversation with Matt Stephens in France. "There's been all sorts of talk about whether he is fat, thin, I've heard all sorts this weekend. He looked fantastic when I was in the bunch [on Sunday]. The one thing with G as I have known for years with him, especially on the track programme, nothing fazes him.
"He is one of the most mentally strong riders I've ever come across. Whether he is at 50%, 80% or 100%, he will race in the same manner and get the result he gets from his physical capabilities. And that could win him another Tour de France, because G at 90% is still an incredible bike rider.
"But Thursday definitely, that will be interesting to see how they play that with Bernal and G, how they run at the Planche de Belles Filles in the final there."
'That was quality' - Team Ineos set red-hot pace in time trial
Thursday's Stage 6 could provide the first real shake-up in the General Classification as it features seven categorised climbs across 157km, with a daunting final ascent to a ski station in the Vosges mountains.
It has been used three times since being introduced to the Tour in 2012 - and each year the man wearing the yellow jersey after the stage has gone on to win the Tour: Wiggins in 2012, Vincenzo Nibali in 2014 and Chris Froome in 2017.
Wiggins believes Thomas will be comfortable in the joint-leadership role and won't expect Bernal to ride for him in the first real mountain test in the Tour.
"You can only deal with the facts you have at the time and I think G will be aware of that," Wiggins said. "He knows that in another race at another time it will be him who is the leader. They can't be deluded, they have to be realistic and they have to ride to their strengths. And you'd say the man in form at the moment is Bernal. The man who should be commanded the respect is G, as last year's winner. I don't think it's a bad tactic to employ.
"Given the choice, do you want Bernal to sacrifice himself for you on the Planche des Belles Filles on Thursday, G would probably be the first person to say, 'not so sure you should do that', because that adds extra pressure to G. So it's not a bad thing to be going along over the next couple of weeks in this joint leadership.
"I think if they both get there on zero time to each other as it were, no time losses, no more crashes in the next few days, I think it's going to be a really interesting couple of weeks."
Listen to the full episode for more from Brad and Matt on:
- The controversy around Mark Cavendish's omission
- A brilliant opening weekend in Belgium
- Why Froome can still win a fifth Tour
- Peter Sagan's chances of winning another green jersey
- What makes the Tour special
- Brad's first weekend on a bike amongst the peloton
- Which teams have impressed so far