The whole time trial v road bike debate is neatly encapsulated by Katusha's Joaquim Rodriguez. The Spaniard gets to the bottom of the first hill on his time trial bike, jumps off and is handed a road bike for the climb. 

Rob Hayles on radio commentary suggests it was a bit of a slow change and any seconds Purito may gain by being on a more comfortable bike could well have already been lost.

Michael Hutchinson, the former British time trial champion says on BBC Radio 5 live Sports Extra that he spoke to Tom Dumoulin's coach this morning and was told that the Dutchman would use his time trial bike because they'd run all the stats through the computer and it suggested that he would be eight seconds quicker than if he used the road bike.

Chris Froome is expected to use his time trial bike too. Geraint Thomas is out on his road bike, perhaps not pushing as hard as he could today because there are two tough days in the Alps to follow.

I wonder what the view out of your office window is like today. The clouds have returned to Salford and the piazza outside is looking sparse.

My colleagues out in France have Mont Blanc to gaze out. #nojealousy

Chris Froome is on his turbo trainer, looking terrific in his yellow skinsuit. He is off in exactly 30 minutes.

A quick flick to Geraint Thomas, who is on Cote de Domancy, the first steep section of the race. There are thousands of people on the hill. Let's hope they give the riders plenty of space to get through.

What colour medals James? #bbccycling

Geraint Thomas has just set off. The Welsh Team Sky rider has again been one of Chris Froome's key domestiques. 

He had hoped to be a little closer to his team-mate in the standings at this stage but an early crash and an ill-timed puncture have not helped his own General Classification ambitions and he is 20 minutes, 15 seconds down.

But, if he gets to ride arm-in-arm with Froome over the finish line in Paris on Sunday, it will very much be a case of job done.

Tom Dumoulin is not sure if he will win today's stage. He told Dutch TV after finishing in 31 minutes, four seconds: "A Froome in top form can easily beat my time."

Rob Hayles on BBC Radio 5 live Sports Extra is not so sure Chris Froome will be chasing a stage win. "He's got one already in this race so the pressure is off in that respect. Also, he doesn't want to be chasing every one-tenth of a second because it could cost him more time.

On how he will ride, Hayles added: "He is able to get all the information at every time check because he is last man off. If I was the team director I would be saying get out at pace because you don't want to switch off and coast. He's got the option of getting to the 10km time check and then gauging it from there."

Former British time trial champion Michael Hutchinson said: I think Chris Froome is going to race his General Classification rivals. This is not an opportunity to take a minute off his rivals, maybe 15 seconds."

In our money, that's an average speed of around 20mph. For a predominantly uphill 17km time trial.

Rob Hayles on BBC Radio 5 live Sports Extra: "I would go full time trial rig because there are enough flat sections."

Keep 'em coming to #bbccycling

Rob Hatch with the answer to Daniel's question: "Very good question. Chris Froome has he luxury of being last onto the course today, and so he'll know exactly how each of his rivals is riding today - if he chooses to get that information. 

"While he would doubtlessly love to win the stage, he's already taken a victory at this Tour, so the pressure is off in that respect. 

"I'm pretty sure he'll go out fairly strongly and will ride the rest of the course depending on how he feels and how his rivals are performing.

"Richie Porte to win the stage but I think Froome's lead will edge closer to three minutes by the end of the day."

You can listen to Rob Hatch and Rob Hayles on BBC Radio 5 live Sports Extra, or via this very webpage. 

Geraint Thomas has also picked Richie Porte to win today's stage in his BBC Sport guide to the race.

#bbccycling for your predictions please.

Trek rider Gregory Rast finished in 36 minutes, three seconds, more than five minutes behind Tom Dumoulin who has just crossed the finish line in Megeve to post the quickest time so far.

If you want a stage win Chris Froome, you need to go quicker than 31mins 04secs, and that's if nobody can beat that before you set off at 15:59 BST.

The new quickest time of the day has been set. Belgian Lotto-Soudal rider Thomas de Gendt has recorded a time of 31 minutes, 45 seconds.

His time in the winner's chair on the finish line could well be short-lived though because Tom Dumoulin is closing in on the finish. 

The Dutchman has set the fastest time at all the time checks and was 37 seconds quicker than De Gendt after 10km.

And send in your questions to #bbccycling 

I'll endeavour to answer them, or they will be tackled by our commentary team of Rob Hayles and Rob Hatch when the BBC Radio 5 live Sports Extra commentary kicks in at 15:00 BST.

Adam Yates, the 23-year-old Orica BikeExchange rider is having a sensational Tour and is an incredible third in the standings, just two minutes, 53 seconds behind leader Chris Froome, not that he's got any hope of catching his fellow Briton.

"He'll be on the top spot of the podium in Paris," said Yates, who is currently wearing the white jersey as leader of the best young rider (under 25) classification..

Of more importance is if he can catch Bauke Mollema, the man in second, who he trails by just 26 seconds after closing the gap by 32 seconds on stage 17.

Will he gain more today?  

This is what he had to say: "Hopefully I won't have a bad day and I won't lose too much time but this time trial suits me more than the other one.” 

Yates starts his time trial at 15:53 BST, three minutes ahead of Mollema. 

Image source, Getty Images

Give young Adam Yates - he's only 23 remember - three more years learning the ropes. By then, Chris Froome will have won six Tours de France and be, at the age of 34, maybe ready to hand over to the Bury climber...and then British riders will continue their domination. Sound like a plan? #bbccycling

Vincenzo Nibali is the latest rider to drop down the ramp and get his time trial under way. The Italian, who won the Giro d'Italia earlier this year, has not really had the legs to help support his Astana team leader Fabio Aru.

He has a decent time trial pedigree and it will be interesting to see if he goes "full gas" today or holds a bit back.

And let me know by how much time Chris Froome will be leading by the end of the stage #bbccycling

I'm going for three minutes, 14 seconds.

If you saw Vegard Breen wondering around like a lost soul near La Caverne du Pont-d'Arc after the time trial on 15 July, here's why.

"Several people came to me and told me the direction of my hotel, but I wasn't looking for my hotel. I was looking for Pokemons."

Two worrying things here:

1. That a professional cyclist is using PokemonGo

2. That he doesn't know that the plural of Pokemon is Pokemon, not Pokemons.

The man who won the first time trial of the Tour, Dutch national champion Tom Dumoulin is out on the road.

Dumoulin is more than 93 minutes behind Chris Froome in the overall standings, so zero danger to the yellow jersey, but he has form and could set the time to beat.

Here's BBC presenter OJ Borg with a little taster from Sallanches. If you are reading via the BBC Sport mobile app, please click on the link to view.