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.

Jean-Christophe Peraud is on the rollers, with his right shoulder bandaged. He crashed this morning in training and fractured his collarbone... but continues.

Andy Schleck is on the first climb and he, more than anyone, will not like what's in stall over the top. The downhill for him will be hellish.

Here comes Jeannesson - he was just 10 seconds down at the first split, but then it started raining, and now he's crossing the finish line just over a minute down on Van Garderen.

Cadel Evans rolls down the ramp. This time two years ago, Evans approached the final time trial knowing that a good ride would put him in yellow. This year, a good ride may just put him into the top 15.

Movistar's Rui Costa, yesterday's stage winner, rolls down the ramp in hsi white Portuguese national time trial champion's jersey. Still dry at the start...

Rolland is almost walking down the descent he's going so slowly. There are going to be some huge time gaps to Van Garderen today.

Pierre Rolland is currently on the first descent and it's very, very wet. The Frenchman wouldn't like this downhill in the dry, but this makes it even worse. His compatriot Sylvain Chavanel, the national time trial champion, is down the ramp on his orange bike.

Team Sky DS Nicolas Portal just told French TV that the yellow jersey Chris Froome will take no risks on the descents in the rain - even if it means losing some time to his rivals.

Richie Porte of Team Sky rolls down the ramp. It will be interesting to see how he rides. The Australian will have his own ambitions, but he'll be under team orders not to take any risks because of the job left in hand. He is, of course, Chris Froome's right-hand man.

Speaking at the finish after his earlier effort, Thomas Voeckler said: "If it rains, the winner will be one of the riders who did the course while the roads were dry." The rain, at the moment, is very localised. Jeannesson, for instance, is getting drenched on his way up the first climb, but Andreas Kloden is very dry going up it.

Here comes Tejay van Garderen - and he's going to be the new leader - by a long way! The American takes 33 seconds off Izaguirre's time and that will be hard to beat - especially if it starts to rain heavily.

The grey rain clouds look very ominous as Jeannesson gingerly makes his way down this sinuous descent, which is riddled with potholes. Some rain drops are falling, but the road is still dry at the moment.

Arnold Jeannesson, third yesterday, has caught Eduoard Vorganov on the first climb. He's going very well - at least, it looks good. Over the summit he goes - but we haven't been given a time split for him yet. The Russian drafts him for a while before dropping back. Ah yes, here we go - Jeannesson has set the second best time, 10 seconds down on De Gendt.

Tejay van Garderen reaches the summit of the second climb to set the new best time at the third split: eight seconds ahead of Izaguirre. The young American then comes to a standstill before changing his bike for the long 12km run down to Chorges.

The rain has started to fall - albeit only lightly, and on the second climb.

Van Garderen takes the third best time at the second split, 23 seconds down on De Gendt. The young American has been third at both splits now.

Peter Sagan, the green jersey, was caught by Cofidis's Rudy Molard on the second climb before crossing the line 3'33 down on the leader Izaguirre at the finish.

Van Garderen crosses the summit of the first climb 22 seconds down on De Gendt's target time at the first split.

Interestingly, the new leader Ion Izaguirre was using a time trial bike - which has not been the norm so far. At least, he finished on a TT bike - we're not yet sure if he started on a road bike for the two climbs before changing ahead of the final descent into Chorges. The Spaniard's average speed for the stage was 35.578 kmh.

Regarding bike changes, the riders are not allowed to change bikes with someone waiting at the side of the road - all bike changes must be made by the support car. A reminder of this rule from Jean-Francois Pescheux may have influenced Tony Martin's decision to change his bike just the once and not the intial three times he had planned.

NEW LEADER! Ion Izaguirre loses time on the descent but manages to cross the line 4 seconds ahead of Westra to set the new target time of 53'58.