Geraint Thomas third on stage 20
GB's Thomas set to win title in Paris on Sunday
Chris Froome moves up to third overall
Tom Dumoulin wins stage and maintains second overall
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Geraint Thomas rolls down the start ramp in the yellow jersey, complete with yellow helmet.
He's ridden a flawless race and knows if he performs to his ability in time trials and gets round safely, a first Tour de France win will be his.
The forecast rain has not belted down. The course is technical but looks to be dry or at least drying out.
Here he goes...
Image source, Reuters
Rob Hayles
Ex-GB cyclist on BBC Radio 5 live, in France
Dumoulin will have to put everything on the line to try and take time back on Geraint Thomas but he also only has 19 seconds on Roglic and he won't want to drop out of second place.
Tom Dumoulin looks resplendent in the rainbow bands of the world time trial champion - a skinsuit made only this morning after the Dutchman managed to lose the original.
What can he do here? He's suggested 2:05 is far too much to make up on Geraint Thomas but he needs to ride to defend second overall from Primoz Roglic and Chris Froome too.
Primoz Roglic won a time trial stage during the 2016 Giro d'Italia.
He also finished second to Dumoulin and ahead of Froome at the 2017 World Time Trial Championships.
Here goes the Slovenian - can he grab second in the Tour de France?
Image source, Getty ImagesIreland's Dan Martin has been given the super-combative award for the most aggressive rider in the Tour de France.
It's well deserved - the UAE Team Emirates leader has animated the race throughout, launching long-distance attacks and counter-attacks, also winning stage six on the Mur-de-Bretagne.
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Rob Hayles
Ex-GB cyclist on BBC Radio 5 live, in France
He's got to concentrate on his own efforts. We know Froome can time trial well and this course should suit him. He is fighting for a position on the podium.
Image source, Getty ImagesRight - here goes the first of the GC contenders that could also win the stage.
Four-time Tour de France winner Chris Froome goes off in fourth place.
He needs 13 seconds to take back third from Primoz Roglic, 32 seconds to reel in Tom Dumoulin.
Can he finish on the podium?
And speaking of Steven Kruijswijk - the Dutchman rolls down the start ramp.
Can he hold onto a top five finish in the Tour? It's been an excellent ride so far for the LottoNL-Jumbo man.
Image source, Getty ImagesThere were rumours this morning that Mikel Landa is not happy about not being the sole leader at Movistar and wants to return to Astana.
He wasn't able to be the sole leader in his previous stint there because Vincenzo Nibali was his team-mate, while he grew frustrated after having to work for Chris Froome at Team Sky. A pattern appears to be developing.
For now, the Spaniard is out on the course, just three second back on Steven Kruijswijk on GC.
Romain Bardet, seventh on GC, rolls down the start ramp to a huge ovation from his home crowd.
Time trialling has proven a weakness for the Frenchman before, having slipped from second to third in Marseille in last year's Tour.
World time trial champion Tom Dumoulin is due off in about 10 minutes, here is what he told ITV4 earlier about the course...
"It's a beautiful course, the organisation did a good job, it definitely suits me but it suits Froome, Roglic and Thomas too so I don't really have an advantage with that.
"It's not that technical, there are some difficult corners but not too much, just up and down the whole way, which is how I like it.
"I've got my eyes on second place, not Thomas. I really want to get on the podium and I hope I have the legs for it."
Dan Martin has a decent buffer over Nairo Quintana of nearly four minutes.
Could he even make up the 1:24 to Romain Bardet in front of him? Time trialling has not been Martin's strong point in previous Grand Tours, mind.
Image source, EPAAdam Yates perhaps went off a bit too quickly all told.
The Briton rolls through into provisional fifth place, 36 seconds down on Michal Kwiatkowski.
That's still a very encourage time trial performance from the 25-year-old at the end of a tough Tour.
Nairo Quintana is a solid time trial rider and should be able to at least hold onto ninth place on GC.
Now we're into the top 10 on GC.
Here goes Ilnur Zakarin...
And here goes Bob Jungels - he needs just over four minutes to overtake Ilnur Zakarin. Any chance he can do it?
Right, we're getting towards the business end now.
Jakob Fuglsang, 12th on GC, rolls down the start ramp.
The Dane needs almost five minutes to overhaul Ilnur Zakarin in 10th, which is unlikely.
And Bob Jungels in 11th is better than both in this discipline.
Image source, ReutersPierre Latour - for some reason named Pierre Roger Latour by Tour organisers, despite that not being his middle name - sets off in the white jersey as best young rider.
He leads nearest rival Guillaume Martin by nearly 20 minutes in that competition so just needs to get round safely to wrap it up.
Winning white would be some consolation for AG2R La Mondiale after Romain Bardet's disappointing Tour.
Adam Yates has slipped back over the second section, going through the second time check 13 seconds down on Michal Kwiatkowski.
Can he make it back up on the climb in the last section?
Even if not, this has been a fine, encouraging time trial from the young Briton.
Image source, Getty ImagesMore from Brailsford to ITV4 on whether other teams could be doing more to challenge Team Sky: "For sure. I don't mean it in a negative way. We didn't know how to win the Tour when we started and made some stupid errors but then brought people in to focus on it.
"Then when we won it we knew what it takes to win and could then refine that more and more. There were one or two Tours where Chris Froome won because he was far and away the best rider and he had less reliance on the team than in the last two years where we've learned more.
"Other teams are doing some brilliant work - LottoNL-Jumbo are doing really well. I've got a network in other sports which has taught me so much and LottoNL have been appearing at those conferences and learning from it. Mitchelton-Scott and Sunweb are doing well too.
"Then there are other teams spending a lot of money but haven't quite got the architecture of their teams. They are still working on that. But we only know what we do so we focus on that and try to stay a step ahead."