Thanks for joining us today - be sure to return for stage 5 tomorrow.
Seraing - Cambrai
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The Thibaut Pinot peloton passes over almost 3:30 down on Martin and the main favourites - that will put the Frenchman well down on GC, almost seven minutes.
The gap was just three seconds in the end for Martin, who makes up for the Etixx-QuickStep meltdown in Zeeland.
That will be the yellow jersey for Tony Martin too - 10 bonus seconds on top of his stage-winning advantage...
Degenkolb pips Sagan for second, with Van Avermaet crossing for fourth.
VICTORY FOR TONY MARTIN! He's so tired he can barely punch the air in celebration...
Degenkolb takes it up - but it's too late!
They have left it too late - Martin looks like he's done this...
Under the flamme rouge goes Martin, who swings onto a small patch of cobbles. He may well do this...
Valverde now leads the chase - Martin has about 5 seconds, but he'll suffer on that final uphill drag.
Giant-Alpecin move to the front now - Degenkolb and Sagan are having a chat. They missed that move by Martin and will need to combine or it will be too late.
Just as Nibali and Degenkolb are shooting the breeze there's an attack by Tony Martin! The German juggernaut has gone for a long one - and he's clearly thinking about the yellow jersey. He needs to finish one second ahead of Froome...
Froome is eating ahead of the finale. He's ridden today's stage very, very well. Quintana, Contador and Nibali have all ridden well in their own separate ways. Pinot is the big loser - three minutes and counting down...
Nacer Bouhanni is in this front group too for Cofidis - he'll be one to watch at the finish.
This will suit Degenkolb to a tee - he must be one of the main favourites, especially with that slightly uphill finish in mind. The second peloton - which includes the green jersey Andre Greipel - is over three minutes back.
Rodriguez, the polka dot jersey, is there too, while Sagan, in the white jersey, is rooted to the back of this group, keeping his powder dry.
Van Avermaet takes it up as the leading group is reeled in. That was a missed opportunity - the eight leaders could have worked well together but didn't. Contador and Quintana are back in it now in this 30-man leading group.
Froome takes it up as Thomas drops back. Van Garderen is also there in this small eight-man leading group. They will soon be caught by the chasing riders - who are being driven by Contador and Tinkoff-Saxo.
They're off the final cobbled section now and it's Geraint Thomas who leads, with Froome in his wheel. it's a group of eight, with Degenkolb, Nibali, Valverde and Stybar. Van Avermaert is there too.
Quintana is stuggling - while Valverde is holding his own. That will complicate matters at Movistar...
Nibali moves to the front but it's Stybar who then edges ahead. He takes Van Avermaet and Degenkolb with him, it seems.
There's some dicey road furniture ahead of the last cobbled segment - Sector 1 at Carnieres. Froome still very well placed - five riders back in the wheel of Thomas. Valverde is there too - but no sign of Quintana.
Pinot has two FDJ team-mates but he's 2:15 down. Pierre Rolland is 1:15 down too. Not a good day for the French. Tony Martin has almost regained touch of the main pack with two team-mates. They're with Sep Vanmarcke, who must have had a flat.
Pinot's meltdown continues - he's having a hissy fit on the side of the road while he waits for a new bike. His GC hopes are over.
Puncture for Tony Martin - that will make it almost impossible for the German to take the yellow jersey today.
Three Tinkoff-Saxo riders on the front: Bennati, Contador and Sagan. They pop a gel each and continue full gas.
Pinot has only just got a new wheel and his face is a picture of utter dejection.
Thibaut Pinot is struggling to keep with the main pack - and he has a puncture now too. Terrible luck for the Frenchman. He will lose yet more time today.
The pack is about 40 strong now with Froome, the yellow jersey, about 15 riders back.
Straight onto Sector 3 at Quievy - and this is the long one at 3.7km. Sep Vanmarcke sets the pace for LottoNL-Jumbo.
It's gradually whittling down. BMC and Tinkoff on the front after that latest section - and the Big Four are all still there.
And now it's Nibali's turn to have a scare - the Italian is forced into the dirt track after Tony Gallopin veers into his path on the next cobbled section, Sactor 3 at St Python.
There are about 80 riders in this main pack, including all the Big Four. it's Alberto Contador's Tinkoff-Saxo team who set the pace now... AND CHRIS FROOME ALMOST COMES DOWN! He's nudged into the gutter by Katusha's Jacobo Guarnieri - and he was really isolated there. Should have been shielded by a team-mate. A wake-up call for Sky.
The pace has slowed and the pack has bunched back up. Astana and LottoNL-Jumbo are on the front with a second peloton riding at 30 seconds. It looks like Pierre Rolland of Europcar is in the second group.
Daniel Oss, with his face bandaged after yesterday's crash, leads the pack for BMC. Quintana is still in this front group - but he's firmly rooted to the back.
Kristoff is chasing back with world champion Michal Kwiatkowski, who must have also had a problem. They're through the latest cobbled section - they come frequently but are very short, encouraging violent accelerations. Three more to go now...
Puncture for Alexander Kristoff of Katusha - he's had a very troubled race so far. BMC and LottoNL-Jumbo lead the pack. Green jersey Andre Greipel is being tailed off...
BMC now on the front now as the peloton hits Sector 4 at Verchain-Maugre, which is one of the uncared for sections that has been left to grass. BMC's bet for the win is Greg van Avermaet but their priority is keeping Tejay van Garderen out of trouble.
Cavendish is right there for Etixx - he's Sean Kelly's unexpected tip for the win today. Nico Roche comes to the front for Sky to calm things down for Froome. It's a group of 40 now on the front of the race.
No sign of Quintana... ah, there he is - the Movistar rider is about 30 riders back and the worst placed of the Big Four. They're off the cobbles and onto some tarmac as the drizzle continues. There are big splits as Etixx-QuickStep come to the front - they have three riders. Barguil and Degenkolb are both there for Giant. Froome is with Thomas for Sky. Contador has at least three team-mates.
Astana have three riders on the front as they hit Sector 5 at Querenaing. Boom and Nibali open up a gap, with Stybar and Vanmarcke. Froome and some others chasing back on...
The break has been caught. It looks like Sagan has helped Contador return to near the front of the main group. Nibali looked so assured over that last section of cobbled. The next one coming right up...
LottoNL-Jumbo have three riders on the front ahead of Astana duo Boom and Nibali. Westra, their team-mate, looks back - he knows the break is about to be caught. The pack has been reduced to about 60 riders, with another group chasing back on.
This is Sector 6 at Artres and Chris Froome, the yellow jersey, is near the front - as is Tony Martin and Vincenzo Nibali. Already an elite group is forming. The four leaders see their gap whittled down to 15 seconds after the pave.
"It looks like Armageddon and that's exactly what we've got," says Carlton Kirby as the riders swing onto the cobbles. The drizzle has stopped and the cobbles are disty and coarse. It's strung out and brutal as LottoNL-Jumbo ride on the front through Sep Vanmarcke.
Alex Dowsett of Movistar has also crashed. It's getting fairly chaotic now that the first cobbled section is in sight - just 1km to go...
Astana now have three men on the front driving the pace - Nibali, Boom and Fulgsang. They have another man in the break - Westra - riding 1:05 up the road.
That crash happened because of a mixture of new tarmac, a tight bend and the drizzle which is now falling. It looks like Richie Porte of Team Sky has been caught up too - he's fighting back on now.
CRASH: An Astana rider and two Cannondale-Garmin riders go down on a slippery bend. It looks like Michele Scarponi, whose fall then prompted Dan Martin and Jack Bauer to go down.
Movistar, Sky, Katusha and Tinkoff-Saxo are all speeding things up on the front of the peloton now. The gap is down to 2:35 with reports of rain on the cobbles coming in... As we pass through the medieval fortified town of Le Quesnoy, it's 10km until the first of six successive cobblestone sectors.
The gap is still 2:50 for the leaders but the sun has disappeared and it's really clouded over. Some rain has been forecast so it will be interesting to see if these cobbles get slippery before the finish. The risk of crashed and incidents will grow drastically if that is the case.
The gap for the four leaders - Lieuwe Westra (Astana), Frederick Brun (Bretagne), Thomas De Gendt (Lotto-Soudal) and Perrig Quemeneur (Europcar) - is still hovering around the three-minute mark. The calm before the storm...
It's also worth noting that we are now in France - the riders having crossed the border shortly after the intermediate sprint. The first town we came to in France was Bavay, renowned for its Roman remains.
Reports coming in from Robbie McEwen - who is working on the race as a pundit for Australian TV - that there is crosswinds on every sector of cobbles coming up. That should spice things up a little.
Issue for Ag2R-La Mondiale's Alexis Vuillermoz, who needs a bike change after clattering into someone and causing a concertina effect in the pack. The Frenchman finished an impressive third yesterday on the Mur de Huy.
Minor crash in the peloton involving Sam Bennett (Bora-Argon 18), Sammy Sanchez (BMC) and Alex Dowsett (Movistar). It looks like there may have been a spectator involved, but it's nothing serious and they're back on their way.
Giant, BMV, Movistar, LottoNL-Jumbo, Tinkoff-Saxo and Sky are all near the front now, with the break rolling at 2:35.
With the peloton's main sprinters opening up a small gap there over the pack, Peter Sagan jokingly suggests they take it up and go on the offensive. Believing the Slovakian is being sincere, Greipel shakes his head in disagreement - until Degenkolb cracks up and his fellow countryman realises it's all just a joke...
Thomas De Gendt (Lotto-Soudal) kicks clear to take the maximum points at the intermediate sprint on the front of the break. When the pack comes clear it's Mark Cavendish who edges Bryan Coquard, with Greipel then pipping Sagan and Degenkolb.
Giant-Alpecin are making their presence known on the front - no doubt for the intermediate sprint coming right up. Their man for the green jersey is John Degenkolb, winner of Milan-San Remo and Paris-Roubaix. Europcar are also there for Bryan Coquard and Lotto-Soudal for Andre Greipel, that man currently in green after his stage two win.
Mechanical for Rigoberto Uran of Etixx. Meanwhile, Movistar come to the front for their man Nairo Quintana. There are a lot of Lampre and Europcar riders there too.
Did you know: Bernard Hinault famously called riding across the cobbles in Paris-Roubaix a "connerie" - stupidity. But he still won in 1981 despite multiple punctures and crashes. In the comic strip Asterix and the Banquet, Asterix and Obelix call into Cambrai - called Camaracum - at the end of the third stage of their Tour de Gaul. Picking up local delicacies in each town, they buy some of Cambrai's famous Bêtises - or humbug - sweets.
It's fairly strung out again on the front of the peloton. The road is quite undulating now with the break on an uphill drag as Westra drops back to his team car for a chat. The Dutchman was eighth in last year's cobbled stage on the Tour. Three minutes for the break now.
It's feeding time for the pack, who pick up their collective musettes on a slight uphill drag. We have the intermediate sprint coming up shortly...
The gap for the four leaders is back up to 3:45. They attacked from the outset to build up a maximum lead of eight minutes - but that came down to just over a minute ahead of the first cobbled section. But now we're back on the normal roads and the sun is out, they've managed to stretch out their lead again.
Sep Vanmarcke (LottoNL-Jumbo) is a potential winner, as is John Degenkolb (Giant-Alpecin) after his Paris-Roubaix heroics. Zdenek Stybar (Etixx) loves the bone-jangling stuff, while Geraint Thomas (Sky) has the skills - it's just a question of whether or not he's let off the leash by Sky. Don't forget Vincenzo Nibali either - he finished third last year in the Tour's cobbled stage... and Jakob Fuglsang, his team-mate, who finished second behind Lars Boom - then of Belkin, now of... you guessed it, Astana.
There will be numerous races going on today: between the escapees, between the Big Four and between those vying for the stage win and the yellow jersey. There are loads of potential candidates to take over Chris Froome's maillot jaune today - with Tony Gallopin (Lotto-Soudal), Greg van Avermaet (BMC) and Peter Sagan (Tinkoff-Saxo) all within 31 seconds of the Briton. There's also Germany's Tony Martin (Etixx-QuickStep) who is just one seconds down on the race summit having narrowly missed out on yellow the past two days.
Alberto Contador is off the back of the peloton after changing his bike. Rigoberto Uran has done the same - and Nairo Quintana by the looks of things too. Probably because they have a fair schlep before the next cobbled section. The letting up of pace has seen the break's gap edge ahead to two minutes.
History: No stage has ever finished in Cambrai before - although it has seen two starts in the past 12 years. When the race featured cobbles last year victory went to Lars Boom, Vincenzo Nibali excelled and Chris Froome crashed out in the rain before the first sector.
That was just a little taster of what's to come: the next cobbled sector is not until 46km to go. That's when we will have six in quick succession before the finish in Cambrai.
Cavendish leads the pack off the first section of cobbles, with Nibali right up there. On the back of the pack, Austria's Marco Haller (Katusha) looks to be in real trouble - he's riding with his right hand off the bars because of the wrist injury he picked up in yesterday's crash.
Puncture for Dutch tyro Wilco Keldeman (LottoNL-Jumbo) as Mark Cavendish (Etixx-QuickStep) sets the tempo on the front.
This is not too bad a section, with patches of the cobbles covered in tarmac to give the riders a little respite. As Sean Kelly says, "It's bad but it's nothing like Paris Roubaix."
The leaders are onto that first cobbled section of Pont a Celles - it's 1800m long and the crowds are pretty large.
The gap is now just 1:35 for those four leaders - Westra, Quemeneur, Brun and De Gendt.
The peloton has split under this fierce pace set by Sky, with BMC and Astana also riding hard. It's totally strung out as Tinkoff-Saxo, Cannondale-Garmin and LottoNL-Jumbo edge to the front too.
Sky are really drilling it now through Ian Stannard and Richie Porte, with the yellow jersey Chris Froome tucked back in fifth position on the front.
Now Katusha, Tinkoff-Saxo and Movistar have edged forward to join the jostling for places on the front of the pack.
Astana and Sky have come to the front ahead of the first cobbled section. The pace is really high as the gap for the four leaders is cut to three minutes. They're onto some cobbles now - but it's just a small segment in a town and will not count.
Sean Kelly: "I'm just hoping it's going to stay dry otherwise we're going to see mayhem - and we don't want that."
Interesting stat: today's 223.5km stage is the shortest distance for a longest stage in a Tour ever.
Chris Froome and his Sky team-mates are riding special bikes today - the Pinarello K8-S - with extra suspension for those cobbles. The Astana team of Vincenzo Nibali are one of numerous teams who have promised they will stop and change their bikes ahead of the final six cobbled segments. That should add a bit of drama to things - as should the weather: there are reports of drizzle and wind near the finish in Cambrai.
The four leaders now have 4:40 over the pack after the peloton upped the tempo and slashed their long lead. Austrian champion Marco Haller of Katusha struggled on the earlier climb but is back with the peloton. The average speed for the first two hours has been 39.4kmph and we're still about 20km away from the first of seven cobbled sections - so don't worry, you haven't missed anything important!
Many apologies for the lack of updates - we have been experiencing some technical difficulties but now look to be back up and running. I'll run you through what we missed...
The peloton crest the summit 7:50 down on the four escapees with the Sky team of yellow jersey Chris Froome controlling the pace.
It was Belgian's Thomas De Gendt (Lotto-Soudal) who crossed the summit in pole position to take the solitary KOM point at the Cat.4 climb to the citadel of Namur, which hosts the one-day GP Wallonia race every year.
A reminder that Spain;s Joaquim Rodriguez picked up the race's first polka dot jersey after his win on the Mur de Huy yesterday. The Katusha rider took 2pts on the Cat.3 climb so will stay in the spotted jersey whatever happens on the Cat.4 climb today with only one meagre point up for grabs.
The gap has ballooned to eight minutes for the four leaders now as they approach the only categorised climb of the day.
Today's Plat du Jour: Liege meatballs swimming in apple and onion gravy and washed down with a bottle of Vapeur en Folie (steam madness) beer - an 8%, hazy amber ale with a white head and a distinctive barnyard feel to it with a not altogether unappealing aroma of overripe, almost rotten fruits (making it almost a hybrid between beer and cider).
Believe it or not: Peter Sagan won in Seraing in 2012 becoming the first rider born in the 90s to win a Tour stage. Chris Froome has only once ridden across cobbles in a major race - for Barloworld in the 2008 Paris-Roubaix, which he abandoned after crashing into a commissaire's car.
The gap is up to almost six minutes now for the four leaders. Perrig Quemeneur is the best place on GC but the Europcar rider is 10:42 on Chris Froome and so no threat to the yellow jersey for now.
The first cobbled sector today comes at Pont a Celles after 101km of racing. It's sandwiched between the only categorised climb of the day - the Cat 4 Cote de la Citadelle de Namur - and the intermediate sprint at Havay. The riders will then pass into France before facing six cobbles sectors inside the last 50km of racing. In total there will be just over 13km on the bone-jangling pave - so expect fireworks this afternoon.
This is the third day on the trot that Europcar have made the day's break - with that man Quemeneur on the offensive for the second time after featuring on the front of the race in the opening road stage to Zeeland on Sunday.
The gap is up to four minutes for the four leaders, who are clearly combining well in the early phase of this stage - the longest in the race.
Michael Matthews continues today despite bad contusions to his ribs. The Australian said he suffered panic attacks last night and found it hard to breathe after finishing the stage in last position, more than 20 minutes down and some seven minutes slower than anyone else. "My goal is just to get to the cobbles and see how it goes and make the time cut basically," he said this morning.
Another non-starter today was Andreas Schillinger (Bora-Argon 18). He was not involved in the crash that marred yesterday's stage, but is suffering from an infection.
The four leaders now have 30 seconds over the pack. Interesting to see Westra there - he was a key figure in last year's cobblestone stage, working effortlessly for Astana team-mate Vincenzo Nibali.
Right from the outset there's an attack from Lieuwe Westra (Astana) and Thomas De Gendt (Lotto-Soudal). They are soon joined by Perrig Quémeneur (Europcar) and Frédéric Brun (Bretagne-Séché Environnement). Game on for the day's break!
Stage 4 of the Tour is now officially under way. It's sunny at the moment in Seraing so no sign of those showers that were initially forecast...
But let's move onto today's stage now as the riders ready themselves in the streets of Seraing ahead of the neutral start of what could be a key day in the saddle... Philippe, the King of Belgium, is present to cut the ribbon at the start of the stage and get the show on the road.
Cancellara completed the stage but later withdrew with a fractured vertebrae - a sad way to end what will probably be the last Tour of his long illustrious career.
The big talking point from yesterday was not so much Froome's yellow or Rodriguez's win - but that horrific high-speed crash 60km from the finish. William Bonnet (FDJ), Tom Dumoulin (Giant-Alpecin), Dmitri Kozonchuk (Katusha) and Simon Gerrans (Orica-GreenEdge) all withdrew straight away, with Daryl Impey (Orica-GreenEdge) and Fabian Cancellara (Trek Factory Racing) joining after the finish. Numerous other riders were affected, with Johan Vansummeren (Ag2R-La Mondiale), Daniel Oss (BMC) and Michael Matthews (Orica-GreenEdge) looking particularly bashed up.
Today the focus shifts to the famous cobblestones of northern France as the race crosses the border and leaves Belgium after three and a half days in the Low Countries. There are six sections of pave in the final 50km of the race so we can expect fireworks - especially if it rains as expected.
Chris Froome finds himself in yellow after his emphatic display on the Mur de Huy - the Sky rider may not have beaten Joaquim Rodriguez, but he finished 11 seconds ahead of both Vincenzo Nibali and Nairo Quintana, and 18 seconds clear of Alberto Contador. What's more, Froome took six bonus seconds for finishing second. He now leads Germany's Tony Martin by one second on GC - but he's 36 seconds clear of Contador, 1:38 ahead of Nibali and 1:56 to the better of Quintana. As for Frenchmen Thibaut Pinot and Romain Bardet, they're now more than three minutes down on GC.
Yesterday, Britain's Chris Froome finished on the back wheel of Spaniard Joaquim Rodriguez on the Mur de Huy to secure the yellow jersey after an incident-filled stage three - with saw overnight race leader, Fabian Cancellara, withdraw after his involvement in a truly horrific high-speed crash.
Hello and welcome to live coverage of stage 4 of the Tour de France - the longest in the race, the 223.5km schlep from Seraing in Belgium to the French town of Cambrai features seven cobblestone sections that could shake things up on the overall standings and see the classics men come out and play.