Welcome to live coverage of stage 17 of the Tour de France, a 32km mountain time trial between Embrun and Chorges near the picturesque Lac de Serre Poncon in the Alps. Race organisers say this is one of the hardest race against the clock that they have come up with - and it features both two climbs and two descents.

We're hearing that Jean Christophe Peraud broke his collarbone in that recon crash this morning, which would rule him out of the rest of the Tour. He was France's only rider in the top ten. That means his Ag2R-La Mondiale team-mate Romain Bardet would be the best placed French rider on GC, in 21st place.

News coming in that Tony Martin plans to change his bike three times during the course - THREE! That's once at each time check - at the top of both climbs and in the valley between. Jakob Fuglsang will change once, while Alberto Contador is said to be using the same bike throughout. No word on Chris Froome yet...

Australian veteran Stuart O'Grady has set the new best time at the first split, coming over two seconds quicker than Jonathan Hivert in a time of 16'19.

Orica-GreenEdge's Svein Tuft, the first down the ramp, is the first to finish, setting a target time of 59'34 at the finish.

We're hearing news that French veteran Christophe Peraud crashed while testing out the course this morning. The Ag2R-La Mondiale rider is currently 9th on GC but hurt his shoulders and has been taken to hospital for tests. Let's hope he'll be cleared to ride later this afternoon. It does show how tricky this course is, however.

So far the riders have opted for standard road bikes. Some have clipped on special aero bars, but many haven't bothered, give the exceptional parcours of this ITT.

Jonathan Hivert also has the best current time at the second check at Picoune, at the bottom of the first descent. The Frenchman crossed the split in 23'26 - which is 3secs faster than Marcel Kittel (Argos Shimano), who came over the summit 11 seconds down on Hivert.

Tony Martin, who won the first time trial at Mont-Saint-Michel, doesn't fancy his chances today. "If I say I am going to win on Wednesday, I might as well say that I am also capable of winning at L'Alpe d'Huez," he said. "With the right motivation and if the circumstances are perfect, then I could get lucky, but this is not a classic time-trial."

Currently, six riders have gone through the first check at the top of the first climb and it's Jonathan Hivert (Sojasun) who has the best time: 16 minutes 21 seconds. Hivert was the last rider to complete the Mont Ventoux stage, incidentally. He finished 50 minutes down on the winner Chris Froome!

Before the top 21 riders, here are some start times to look out for: Geraint Thomas (Sky) 09:49, Lieuwe Westra (Vacansoleil-DCM) 10:15, Jonathan Castroviejo (Movistar) 11:37, Tony Martin (OPQS) 11:39, David Millar (Garmin-Sharp) 11:51, Thomas De Gendt (Vacansoleil-DCM) 12:05, Peter Kennaugh (Sky) 12:35, Tejay van Garderen (BMC) 13:25, Richie Porte (Sky) 14:23.

The riders are leaving at intervals of two minutes at the moment, until 21st place Daniel Moreno (Katusha) who will be the first to leave with a gap of three minutes. Dan Martin (Garmin-Sharp) will be the first rider in the top ten to roll down the ramp, at 15:06 UK time.

We have three time splits today, coming at 6.5km (summit of the Puy-Sanieres), 13.5km (the bottom of the first technical descent at Picoune) and 20km (the summit of the second climb at Reallon).

The sun is out and it's a cooler 22 degrees Celsius. There had been talk of rain in the afternoon yesterday so we will have to wait and see it that materialises - that would make things trickier for the race favourites, but perhaps more interesting for us viewers...

Sven Tuft leave the starting house to get this intriguing ITT under way. The Canadian finished 6th in the last time trial at Mont-Saint-Michel after leading for a long period at the start. The thing is, today's parcours is an entirely different preposition, what with the two climbs, so he will not place so high.

The first rider to roll down the ramp today will be Canada's Svein Tuft, the Lanterne Rouge from Orica-GreenEdge. Tuft will start at 09:17 UK time, with Team Sky's Chris Froome, the yellow jersey, not in action until 15:33 UK time.

Finally, Peter Sagan has all but won the green jersey thanks to a 99-point lead accrued over the past couple of weeks. The Slovakian youngster tried to get into the main break yesterday but his move was foiled. Given the terrain over the next few days, he may well have to wait until Paris to add to his huge 377-point tally and add to his solitary stage win. Given his Tour, however, he'll probably finish second on the Champs Elysees like he has on four occasions so far...

As just mentioned, Colombian climber Nairo Quintana is the white jersey as best young rider. The 23-year-old from Movistar actually moved one place higher into 5th place on GC yesterday after Dutchman Laurens ten Dam (Belkin) missed the split on the final climb. Poland's Michal Kwiatkowski was also distanced on the climb, so the OPQS rider drops a bit further back on both GC and also the battle for white. He trails Quintana by 3:50, with American Andrew Talansky (Garmin) third at 7:45.

Froome retains his polka dot jersey ahead of three successive days in the high mountains - although once again it will be the Spaniard Mikel Nieve (Euskaltel) who wears the spotted outfit. Nieve is in fact third on the KOM standings but wears the polka dots because Froome is in yellow and Nairo Quintana is in white. Froome has 83 points, Quintana 66, Nieve 53 and former leader Pierre Rolland is on 51.

Britain's Chris Froome survived a scare on the final descent of the stage to retain his yellow jersey by 4:14 ahead of Dutchman Bauke Mollema and a further 11 seconds over Spaniard Contador. Pressing on the notoriously dangerous descent into Gap, Saxo-Tinkoff's Contador crashed on one tight bend 6km from the finish, forcing Team Sky's Froome to veer to his left, ride off the road, unclip and then steady himself before continuing on his way alongside his remounted rival.

Yesterday, Portuguese all-rounder Rui Costa soloed to victory after attacking from a break on the final climb of the day. The Movistar rider finished ahead of three Frenchmen - Christophe Riblon, Arnold Jeannesson and Jerome Coppel - to deny the host nation a first win on the Tour. Costa's 11-minute advantage over the main pack of favourites makes up for the same amount of time he lost in coming to team-mate Alejandro Valverde's assistance after he punctures in the crosswinds last week...