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As it happened: Test day four
By Pablo Elizalde, Matt Beer and Jamie O'Leary
The live commentary has ended. No further updates will be posted.
07:57 Good morning and welcome back to Barcelona for the final day of Formula 1's second 2012 pre-season test.

08:00 We're just about ready to get going, but Marussia won't be out for a bit, as @Marussia_F1Team explains: "Five minutes til the session starts but looks like we'll be in the garage. Some work being done to the car."

08:00 But it's green for everyone else.

08:00 And it's warm!

08:01 Well, warm-ish. At 13 degrees track temperature and seven degrees in the air, it's the hottest morning of the test so far.

08:01 Mark Webber, Paul di Resta and Jean-Eric Vergne make a prompt start.

08:01 Warmer temperatures might help persude some teams to run earlier - some said last night that the mornings were simply too cold to be useful.

08:02 Today we're expecting temperatures to get as cosy as 16 degrees later on.

08:02 Kamui Kobayashi and Heikki Kovalainen also complete installation laps.

08:02 Kovalainen's Caterham is first back into the pits.

08:03 The rest of the early quintet follow the Finn in, as Pastor Maldonado and Jenson Button head out.

08:04 Maldonado was quickest yesterday, which came as a bit of a surprise as Williams's form hadn't been stunning in testing so far:

Maldonado quickest on day three

08:05 Felipe Massa joins the fray, which means only Nico Rosberg and Charles Pic haven't been out.

08:05 And as we say that, here comes Rosberg.

08:05 So it's just Pic to go, and Marussia has already admitted it has an issue to solve in the garage before it can join.

08:06 This will be Pic's third day of running. This week is all about giving the rookie plenty of mileage, and he's back in the 2011 Virgin today after Timo Glock had a quick Thursday outing.

08:06 Massa becomes the first man to stay out past the opening lap.

08:08 Massa now comes in, so the track is quiet.

08:08 We were saying a moment ago that Maldonado going quickest yesterday was a bit of a surprise, but the man himself said the Williams is fast and getting even better:

Maldonado: Williams taking big strides

08:10 If the Williams turns out to be brilliant, that might leave the team's ex-driver Rubens Barrichello feeling a bit peeved. AUTOSPORT Plus subscribers might like to read an exclusive interview with him about how his Williams exit was handled and why he's so fired-up about IndyCar:

Barrichello: I'm smiling, big time!

08:11 Crowd watch: Three people in the main grandstand so far. Good morning to them.

08:12 Although when we loosened the chains to the media centre desk and had a quick trackside jaunt yesterday, there was a good number of people on the infield.

08:12 It takes a big crowd to make this place look full, but the test has been deceptively busy.

08:15 Di Resta heads out, allowing us to stop counting people and watch a car.

08:17 Kobayashi and Button head out to join di Resta.

08:18 If you didn't hear the rumours yesterday, Red Bull dismantled its pit wall 'prat perch' and gossip spread that the team was packing up and going home. It wasn't, it's still here.

08:18 But it and Ferrari are changing their testing plans slightly:

Ferrari, RBR change final test plans

08:19 Will this lead to a repeat of the epic AUTOSPORT Live day last year when we commentated on four cars doing very little in pouring rain all day in the final 2011 test session? Who can say...

08:19 Still no laps on the board as di Resta heads in. But Kobayashi is starting his first flying lap.

08:20 Massa sets off too, Button makes a quick pit visit then rejoins, and Vergne follows them.

08:20 Kobayashi gets us underway with a 1m26.955s lap.

08:21 Sauber has tended to be the first to put in times all week.

08:25 The Japanese driver stays out and his next lap is in the 1m27s.

08:25 Kobayashi is running on super softs, while Webber and Vergne pit with medium tyres on their cars.

08:25 Rosberg now on track again too.

08:25 The Mercedes, which had been on softs, now pits.

08:26 Vergne quickly comes back out, with Kovalainen doing likewise.

08:30 Kovalainen, on softs, sets a 1m29.937s, then gets down to 1m29.456s.

08:30 Vergne is still heading in and out of the pits with logging a lap yet.

08:31 Rosberg also avoids setting a time as he pits then rejoins.

08:34 Invigorated by breakfast at Sauber, @eddstrawF1 fires up his laptop.

08:35 As Kovalainen sets a new personal best of 1m28.853s.

08:35 Only Kobayashi and Kovalainen have set times so far, though plenty of other drivers are diving in and out, including Maldonado, Rosberg and Webber.

08:36 Kovalainen swaps track space with Maldonado - the Finn heads in and the Venezuelan returns.

08:37 @clubforce tells us what Force India is up to: "We've started the day with more aero work - running sweeps on the front of the car."

08:38 Di Resta, on medium tyres, sets a 1m28.967s.

08:38 Maldonado is running on soft tyres but hasn't set a time yet.

08:40 @eddstrawF1 picked up the inside line on Sauber's plans while eating the team's breakfast: "Kobayashi is doing some aerodynamic comparison runs at the moment. The plan is to stick to super softs and do a performance run in the hour before lunch."

08:41 Di Resta has now got down to a 1m27.684s, as Maldonado starts off with 1m31.200s.

08:41 Massa is on a lap on medium tyres, while Kobayashi is now on hard tyres for another of those aero comparison runs.

08:42 Massa jumps to the top with a 1m25.278s.

08:43 Massa's times came on his second flying lap of a run on medium Pirellis.

08:43 Maldonado does a personal best of 1m30.436s on softs.

08:44 Massa's time on this lap is up to a 1m26.860s.

08:46 Massa does a 1m25.176s, knocking a tenth off his previous benchmark.

08:46 Kobayashi, who was fastest for a while, is now lapping at 1m29s dead on his hard tyre aero comparison run.

08:46 Kovalainen improves to 1m27.047s in third place with his first flying lap of this run.

08:48 Webber heads out again, having only banked three laps so far today.

08:48 Over half the testing field is on track at the moment, with Ferrari, Caterham, Force India, Williams, Red Bull and Mercedes pounding round.

08:52 Webber pits again and the engine goes off.

08:53 Massa comes in, while Vergne is setting out again and di Resta is on an out-lap after a brief pitstop.

08:54 Di Resta, Vergne and Kovalainen are on medium rubber, and Maldonado is on softs.

08:54 A new best from Vergne, who does a 1m26.975s to go third.

08:54 And di Resta comes back in.

08:55 Di Resta and Kovalainen both pit.

08:55 Maldonado improves to 1m30.407s but is still slowest among those who have done a flying lap.

08:56 Now Vergne shoots up to second on a 1m26.551s.

08:56 Kobayashi leaves the pits again.

08:58 Rosberg is now back out as well, this time on soft tyres.

09:00 With an hour gone, Massa remains quickest with a 1m25.176s, followed by Vergne, Kobayashi, Kovalainnen, di Resta and Maldonado. No times yet from Webber, Button or Rosberg, and Pic has yet to emerge from the garage.

09:00 Di Resta has the most laps so far at 18, followed by 17 for Maldonado and 16 for Rosberg - all of the latter's being in/out laps.

09:01 Maldonado comes in and ends a run of 14 flying laps.

09:02 Most of his laps were in 1m30s, with an average of 1m31.177s as a few laps were up in 1m33s.

09:02 For a moment, Kobayashi had the track to himself, then he pitted too, and now Webber has emerged.

09:02 It's getting warmer too, track temperature up to 20 degrees, air temperature to nine degrees, and no word to speak of.

09:02 Kobayashi sets off again too.

09:04 Kobayashi does a slow run down the straight with a few downshifts thrown in.

09:06 Webber improves to sixth place with a 1m29.435s.

09:06 Button sets off too.

09:07 The McLaren hasn't set a time so far today.

09:07 Another improvement from Webber takes him to fourth on a 1m27.001s.

09:08 Button is on the hard Pirelli tyres

09:09 Webber moves up to second with a 1m26.209s

09:09 Button has also improved, relegating Webber back to third

09:10 A 1m25.367s for the McLaren driver on his fifth lap of the day

09:10 Webber pits as Massa heads out again

09:11 That was a three-lap run for Webber

09:11 Button is now quickest with a 1m24.651s, still far from the best times seen this week

09:11 Button's time has been set on the hard tyres.Massa is on mediums

09:12 Rosberg out of the pits. Doing a practice start as he joins

09:13 The Mercedes driver is yet to set a time, despite appearing with 18 laps in the timesheets

09:13 Yesterday's pace-setter Maldonado joins the action in the Williams

09:14 A 1m24.981s for Button on the ninth lap of the day

09:15 Rosberg posts his first timed lap of the day: a 1m28.789s that puts him in eighth

09:15 He's still over four seconds off the pace though

09:16 Rosberg is back at the bottom of the times as Maldonado improves to a 1m27.511s

09:17 Four laps so far for Massa in this run, mostly in the 1m26s

09:17 Rosberg is on hards, Maldonado on softs, Massa on mediums. Kobayashi has joined the track on mediums too

09:18 Rosberg has set a new personal best - 1m27.880s - but he is still slowest

09:19 Charles Pic is yet to take to the track in the Marussia

09:20 Kobayashi is back in the pits after just one very slow lap

09:21 Massa, lapping in the 1m27s, is currently the quickest man on track. Maldonado running in the 1m29s, Rosberg in the 1m28s

09:22 Rosberg now pits to end that stint.

09:25 Vergne's fastest lap came on soft tyres and including the best times of the day in all three sectors.

09:26 Kobayashi comes back into the pits on hard tyres, while di Resta rejoins.

09:27 The Force India is now running on medium tyres.

09:28 Di Resta makes a big improvement with a 1m25.086s to go third.

09:29 That was on his second flying lap of this run.

09:30 Still getting warmer as the track temperature reaches 23.3 degrees and the air temperature hits 11.7. We're expecting heights of 16 degrees later.

09:30 Vergne comes into the pits.

Kovalainen09:32 Won't be seeing Kovalainen for a bit, news from @MyCaterhamF1: "We've found an electrical issue with the engine which requires an engine change. Should take about 90mins so will be back out again asap."

09:37 The track went quiet for a spell, but now here comes Maldonado again.

09:38 Kobayashi and Button come out too.

09:40 Maldonado trims a tenth off his best time to get down to a 1m27.447s. The Williams stays eighth - no repeat of yesterday's heroics yet.

09:42 Kobayashi shoots to the top of the times with a 1m23.921s, as Button improves to 1m24.433s but finds himself actually knocked down a position to third as the Sauber leaps forward.

09:42 Maldonado does now gain a position too, as he puts in a 1m27.006s and edges up to seventh ahead of Kovalainen.

09:44 Button's time came on hard tyres, while Maldonado, Massa and Kobayashi are all out on mediums.

09:44 Another little improvement from Maldonado, who goes a whole hundredth faster and does a 1m26.969s.

09:45 Maldonado going quickest of all yesterday counted as a surprise, it's fair to say, as Williams hadn't looked stunning in testing so far.

09:47 So that's the theme of our question for today - what has surprised you most in testing? Good or bad, happy or sad, we want to know what's caused your eyebrows to raise. Email with your comments and we'll publish as many as we can in our Live coverage.

09:47 And you can also email with any questions you have for our team of experts at the track.

09:49 The only car we haven't yet seen on track today is the Marussia. @eddstrawF1 has learned that a problem has been found with a suspension part and Pic won't be out for a while.

09:53 Vergne, di Resta, Maldonado and Rosberg are on track right now, and we'll bring you a rundown of their average pace when their stints finish.

09:53 But for now, to the mailbox to see what's surprised you in testing so far...

09:56 Before that, di Resta jumps to third with a 1m24.327s.

09:57 Selim from Istanbul says his big surprise of testing so far is: "Red Bull doesn't look good as I expected. Lots of technical issues. I think McLaren and Mercedes can be surprise leaders of first races."

09:59 Yousef says: "The biggest shock for me in testing was Lotus's chassis problem. It really shocked me, but I was even more shocked that they pulled out of the Barcelona testing and can't use the chassis that they used in Jerez."

10:00 Earlier this morning, Lilly asked if we knew if any of McLaren's big bosses - Martin Whitmarsh, Sam Michael and Paddy Lowe - had attended the test, as they hadn't appeared in pictures.

10:01 Button goes quickest of all on a 1m23.200s.

10:01 (Good timing as we were just answering a McLaren question)

10:01 The former champion's time puts him 0.721s clear of Kobayashi's Sauber.

Jenson Button10:02 So to answer Lilly's question, @eddstrawF1 has been on McLaren watch and reports that he has definitely seen Paddy Lowe, hasn't set eyes on Sam Michael but is sure he would be here, and knows that Martin Whitmarsh was due to drop in.

10:07 Kobayashi sets a new personal best too, but it only trims 0.007s off the gap between him and Button.

10:08 Maldonado finds more time too, doing a 1m24.667s on medium tyres.

10:08 But he swiftly loses his fifth place to Webber, who does a 1m24.391s.

10:09 Rosberg onto his first flying lap of this run.

10:10 Rosberg improves to 1m27.258s but remains at the bottom of the list.

10:11 Ranaganathan emailed to ask how teams decide whether to run from Thursday to Sunday at the next test or Friday to Monday as Red Bull and Ferrari will do, and if a traffic-free environment was the aim.

10:11 @eddstrawF1 explains all: "While the teams do arrange the 15 days of group testing between them, there is a certain amount of flexibility. Red Bull and Ferrari have decided that they want to bump the test back by 24 hours to give themselves more time to manufacturer the upgrades they want to try before Australia. Bascially, buy themselves another day. And it is literally a case of buying another day. Both teams will still be contributing to track hire for March 1, when they don't run, but will have to split the cost for March 5 between them

"The relatively clear track is a bit of a help, but the main thing is the extra 24 hours of pre-test working time that it buys them. Other teams might be tempted to do the same, but it would cost them."

Mark Webber10:12 Webber has pitted, having done just three laps on that run - a 1m31s followed by two mid-1m24s.

10:14 Button is back in now too. The 1m23.200s that put him to the top of the order was his sole flying lap of that run.

10:15 Kobayashi's personal best in second place was also at the start of a short run - he did that 1m23.9s, backed right off, then did a low 1m25s before pitting.

10:15 Banner watch: The Schumacher banner is now hanging limply from one corner.

10:16 Only the Kubica (poignant), Alguersuari (slightly scary) and Alonso (standard) banners remain.

10:17 Jacques says his surprise of testing so far is "the poor reliability of Caterham. I'm starting to be worried for the team. Sure Tony Fernandes must be boiling!"

Paul di Resta, Force India10:18 Di Resta improves to second in the Force India, delivering a 1m23.304s lap to put himself 0.104s behind Button.

10:21 Button's quick time came on super softs, we think.

10:22 While Kobayashi was on mediums, and di Resta's recent jump came on softs.

10:24 Button is now on hard tyres and just did a 1m23.442s, including his best time of the day in sector one. Now he returns to the pits.

10:24 Rosberg is also out on hard tyres.

10:25 Button is swiftly back out, with Massa coming out as well.

10:27 The McLaren doesn't stay out long, here it is in the pits again.

10:28 Button's best time earlier was set on hards, not super softs, it turns out.

10:28 We're going to wash @eddstrawF1's eyes out.

10:28 Massa does a 1m24.454s and moves up to sixth.

10:29 The Ferrari is running on medium tyres, as is Maldonado, who completes his 69th lap of a busy morning.

10:29 Back to the inbox, where you're telling us what has surprised you most in testing so far...

10:30 Dave says: "Can't say I'm a massive fan of the Ferrari team but I'm very surprised that so many people are writing them off at this stage. They're obviously still sorting out their correlation issues and gathering huge amounts of data. When they get on top of this, I'd expect very quick development as they throw their vast resources behind the team. Don't write off Ferrari just yet."

10:32 @eddstrawF1 is so ashamed of his Button tyre identification error, he has left.

10:32 Most probably to go trackside rather than for a self-flagellating walk back to the UK, though.

10:32 Christian from Stockholm says the big surprise for him in testing is that the pecking order seems to be the same as last year.

10:32 What's surprised you in testing so far? Email and let us know.

Pastor Maldonado10:34 Maldonado has pitted after a massive 33-lap run, including a mid-stint tyre change. The Williams averaged a respectable 1m27.218s and was running on medium tyres.

10:35 Rosberg and Kobayashi go back out.

10:37 Pravin says the biggest surprise of testing for him so far is that there haven't been "any extremely good teams like Brawn in 2009 or extremely bad like McLaren in 2011. It's very hard to know who's underperforming and who's sandbagging."

10:38 Rosberg gets his time down to a 1m26.690s, but remains eighth.

10:38 Di Resta heads out, while Massa just ended a run with a practice pitstop.

10:38 Kobayashi surges back to the top with a 1m22.749s lap.

10:38 The Sauber usurps Button's McLaren by 0.451s.

10:39 That's the first time all day anyone has gone below 1m23s, and included the best sector one and two times of all.

10:40 Red flag.

10:41 Thierry and Suvra both pick Force India as the positive surprise of testing so far, both for pace and reliability.

10:41 And just as we run their comment, the Force India stops at Turn 9 to bring out this red flag.

10:41 Di Resta is in the gravel and sideways.

10:41 Which suggests he hasn't run out of fuel...

10:42 Kobayashi's new benchmark time a few moments ago was set on medium Pirellis, by the way.

10:42 Looks like di Resta lost the rear through Campsa.

10:43 That said, he hasn't gone far into the gravel at all considering Campsa is a quick turn.

10:43 Di Resta is out of the car, and a horde of marshals are relishing having something to do after a serene morning so far.

10:44 The car is now being hitched up onto the truck.

10:44 A frankly baffled Sam Tremayne says there are no obvious tracks into the gravel except "sort of behind the car".

Sauber10:46 "All is running smoothly so far" reports @OfficialSF1Team as its car sits fastest.

10:47 No covers on the Force India yet as it is moved onto the low loader.

10:48 To pre-empt questions from observant readers, the picture of Kobayashi below would have come from one of his installation laps - he didn't just go fastest on grooved tyres.

10:48 The track vehicles move away and the marshals trudge back to their corners as recovery of di Resta's Force India is completed.

10:49 David is the latest man to add himself to the 'Force India is the surprise of testing so far' club in the inbox. "This car looks a beauty - fast and fresh," he said. "As a Lotus fan, I am afraid!"

10:51 Tristin picked Toro Rosso as his surprise of testing, saying he "is no big fan" but "stuck a sneaky euro on Toro Rosso for the constructors' title at 200/1 the other day. Seems to be going well - top five in every day of testing. Maybe something from Red Bull is finally rubbing off. Big ask with two new drivers though!"

10:51 @eddstrawF1's assessment of what happened to di Resta at Turn 9: "looks like he understeered off and got bogged down."

10:53 Asier from Basque Country says: ""My biggest surprise is the good shape of McLaren. Although all we know they are one of the best teams ever, watching their single seater as the only one without a 'duck nose', made me think they had gone wrong again, and I was expecting a bad season like 2009. Hopefully it seems I was wrong and as a big McLaren fan I feel I will enjoy this season watching my team fighting for the championship right from the beginning. Go McLaren!"

10:53 Back to green at Catalunya.

10:54 Rosberg, Kobayashi and Massa lead them out.

10:55 Christian says "I think the reliability of the Williams FW34 is very surprising for me, but in a good way!"

10:56 Maldonado's 71 laps already this morning certainly bear that out.

10:56 Kobayashi wasting no time in going even quicker than before as he delivers a 1m22.520s.

10:56 New best times in sectors one and two, but a lock-up at the chicane, as spotted by our man trackside @eddstrawF1.

Felipe Massa10:57 Massa improves to a 1m23.563s and jumps from sixth to fourth.

10:58 Kobayashi is on soft tyres on this run.

10:59 As are Massa and Vergne, with Rosberg on hards.

10:59 Massa backs off in the final sector to let Rosberg pass.

11:01 A quick recap with three hours gone: Kobayashi is quickest on a 1m22.520s, 0.6s ahead of Button, with di Resta, Massa, Vergne, Webber, Maldonado, Rosberg and Kovalainen following, but no time from Pic yet due to a suspension issue.

11:02 Maldonado and Rosberg have already done a mammoth 71 and 65 laps respectively, while Pic aside the lowest tally is Kovalainen's 16 as an electrical problem has forced Caterham to do an engine change.

11:02 Massa comes in for another practice pitstop and again it's the end of his run as he cuts the engine straight after.

11:04 Today we're asking you to let us know what's surprised you most in testing so far. Common themes right now are how good the Force India is, and how quick people have been to dismiss Ferrari. Email to have your say.

11:05 "Ugly noses surprised me," said Dinko Tanev. "I hope at least Marussia and HRT join McLaren in having normal noses on their cars. But I won't be surprised if some teams do plastic surgery for the first race."

11:07 Kobayashi is back in the pits after the five-lap run that started with the fastest time of the day so far. After that, he backed off a little with a 1m27s, then did two 1m24s interspersed with a slow lap.

11:09 Into the final 50 minutes of the morning, and approaching the optimal conditions. Ambient temperature of 16 degrees, track temperature a more impressive 32.

11:10 Maldonado can't get enough mileage today, he heads back out in the FW34, followed by Massa in the F2012.

11:12 Maldonado does a new personal best of 1m24.244s to move up to sixth.

11:14 The Williams driver is on medium tyres.

11:14 Button and Rosberg are running hards, while Massa is on softs.

11:15 David Surgenor emails with his nomination for the surprises of testing so far: "The strong likelihood that Mercedes has leapfrogged Ferrari (though they will come back hard) and the obvious sandbagging by the top three teams who all seam to have a couple of seconds in their pockets. There is no way that Sauber/Williams/Force India/Lotus are fastest!"

11:15 Maldonado improves again to a 1m24.183s.

11:17 Kobayashi lowers his benchmark further as he laps in 1m22.312s, putting him 0.888s clear of Button.

11:17 Maldonado and Rosberg come into the pits.

11:18 That was a consistent 14-lap run from Rosberg, all in 1m27s and 1m28s, averaging 1m28.130s.

11:18 Might be a race simulation as the Mercedes blasts straight back out after a pitstop and immediately does a new personal best in sector three on its out-lap.

Nico Rosberg, Mercedes11:20 Now a new personal best from Rosberg as a 1m24.092s moves him past Maldonado for sixth.

11:22 The German is running on hard tyres after his pitstop.

11:31 Vergne, on supersofts, does a 1m23.792s but stays fifth.

11:31 Plenty of marbles on those tyres as the Toro Rosso comes in.

11:32 Into the final half hour of the morning, when typically we have seen the best times set.

11:32 Sure enough, Maldonado pops up to second with a 1m22.561s.

11:33 That's a quarter of a second off Kobayashi's time and includes a new overall best time in sector three.

11:34 The Williams is running on super softs.

11:36 Webber is next man to improve, doing a 1m23.774s and going sixth.

11:38 Dr Tim Havard emails live@autosport with his nomination for the surprise of testing so far: "Force India have been impressive but I am surprised that more comment has not been made about Sauber. Their car has shown impressive pace and pretty good reliability. Is it because we are used to Sauber being perennial midfield underachievers that we tend to overlook them? They certainly have two hard charging racers in their cars.

"I have a feeling they could spring a surprise this year - do a Newcastle if you want to use a footballing analogy."

Mark Webber11:38 That time from Webber came on soft tyres.

11:38 Rosberg and Button are out on hard tyres.

11:40 Maldonado and Rosberg pit, as does Webber, leaving just Button on track.

11:42 Aaron emails essentially to say that he wants our job, then adds: ""Oh and my surprise of the season is the lack of Ferrari's progress. It really seems they have started on the back foot, but testing is testing for a reason!"

11:42 Vergne heads out.

11:44 Excited Sauber fan Daniel Gerber is keen for us to confirm that Kobayashi's time at the head of the field right now is the fastest of 2012 so far at Catalunya. You're right Daniel, the Sauber pipped yesterday's benchmark from Maldonado by a few fractions of a second.

11:46 Massa is next to go out.

11:47 Anirudh says the big surprise of testing for him is that AUTOSPORT Live hasn't recruited Karun Chandhok, as he suspects he's be pretty good...

11:47 And adds: "But on a car front, I should say that I'm surprised that Lotus found a chassis problem that wasn’t detected in the design stage – strange."

11:48 Kobayashi sets off again as the lunchbreak edges closer.

11:52 No time from Kobayashi on that run, he comes straight back into the pits.

11:52 Button, di Resta, Massa and Webber are now out.

11:53 This is the first time di Resta has been out since he got stuck in the Campsa gravel earlier, but Force India was able to swiftly get the car cleaned up and back on track.

11:54 Button is onto lap 12 of a run that has been consistently in 1m28s.

11:56 Massa pits quickly and rejoins on super softs.

11:56 Kobayashi also comes in and out, on medium tyres.

11:56 Di Resta and Webber cross the line almost nose to tail.

11:58 Massa pits again and once again immediately heads back out - so not giving us a great indication of what Ferrari can do on super softs.

11:58 Kovalainen news from @MyCaterhamF1: "The engine, gearbox and floor are now back on and we'll be firing up again soon"

11:59 Di Resta pits to end his run, Kobayashi dives in then heads back out, and Maldonado leaves the pits too.

11:59 Maldonado is on super softs - will this be a last-gasp quick time before lunch?

12:00 Chequered flag comes out.

12:01 No improvements on those last laps, so the half-time order is Kobayashi fastest from Maldonado, Button, di Resta, Massa, Webber, Vergne, Rosberg and Kovalainen.

12:01 The Caterham missed most of the session as an electrical issue prompted an engine change, and Pic has not been out at all due to a suspension problem on the Marussia.

12:02 Rosberg has the morning's top lap tally with 92, then Maldonado on 85 and Kobayashi on 62.

12:02 We're going to revive ourselves with lunch, see you in just under an hour.

13:03 And we are back, and the green flag is out for the final session of the week!

13:04 Unfortunately there is no one on track at the moment, so there's little to report

13:04 Scrap that, Kovalainen heads out in the Caterham

13:06 Kobayashi joins the Finn on track

13:07 Or not, Kovalainen heads straight back into the pits

13:08 Button heads out in the McLaren. Fifty laps from the 2009 world champion this morning, remember. He's currently third fastest.

13:09 @MyCaterhamF1 1st post-lunch installation lap done. Heikki: "All good. No dramas." Quick turnaround ordered by Juan then we're straight back out.

13:13 The Juan, to which Caterham is referring, incidentally, is Kovalainen's race engineer Juan Pablo Ramirez.

13:14 Button pits, so Kobayashi has the track to himself...

13:14 But not for long. Kovalainen heads out to join him. Button rejoins the fray as well.

13:15 Just 17 laps in the bag for Kovalainen following that engine change this morning. He and the Caterham team will be hoping for a trouble-free run this afternoon.

13:17 Nico Rosberg heads out to join the party in his Mercedes.

13:17 A marathon 127 laps for Michael Schumacher yesterday, and Rosberg has already notched up 92 today! That's six more than Pastor Maldonado and a lot more than anyone else.

13:20 Rosberg and Kobayashi are out on the soft Pirellis while Button and Kovalainen have hard rubber for the moment.

13:21 Paul di Resta slips out onto the track.

Heikki Kovalainen Caterham Barcelona test 201213:23
A nice arty shot of Heikki Kovalainen here from this morning, before the engine in his Caterham needed changing. The light's much better now so some clearer shots should be coming through from the snappers this afternoon. Don't forget you can see the best images from all four days in our Barcelona gallery.

13:24 Rosberg returns to the pits, but goes back out immediately, followed by Jean-Eric Vergne's Toro Rosso.

13:25 The Frenchman is on softs - thanks to our intrepid trackside tyre stalker Sam Tremayne for that.

13:25 Di Resta is on medium rubber, but he's trying desperately to get heat into the tyres, weaving across the line as he completes a lap in over 2 minutes.

13:28 @InsideFerrari Just like yesteday, we're doing a big set-up change on the car, so don't expect to see us running soon.

13:30 Di Resta's back into the pits.

13:31 Rosberg and Vergne join him.

13:33 In case you've only just joined us, find out what's happened so far in our morning report.

13:37 Good support in the grandstand for the British drivers. A few union jacks around and lots of other branded coats and jumpers for the McLaren boys and Di Resta. Although Ferrari appears to be winning the battle by a small margin from Red Bull.

13:38 Button pits as di Resta goes out.

13:38 Daniel Ricciardo makes his way out to the Toro Rosso prat perch. He's not driving today, but he looks pretty interested in what's going on.

13:47 Kovalainen pits, as does di Resta. So just Kobayashi remains on track.

13:47 Button heads out onto the track now.

13:48 Rosberg leaves the pits just as Button comes past to start a flying lap; the McLaren sweeping past the Mercedes into Turn 1.

13:48 Vergne, Rosberg and Button are all on softs, di Resta has the supersofts and Kobayashi - on his 25th lap of this run - has mediums.

13:49 Di Resta sets his best lap of the day. A 1m23.119s lap moves him ahead of Button and into third.

13:50 Rosberg is also making progress. A 1m23.843s lap is two tenths quicker than he's been today. He stays eighth, although now less than a tenth behind sixth placed Webber.

13:51 Kobayashi heads into the Sauber pit bay.

13:57 Fans of Sam Bird - who has undertaken a fair bit of testing for Mercedes over the past two years - rejoice. Your man has a race seat for the coming season.

13:58 That announcement leaves the Formula Renault 3.5 grid looking a tad stronger than that of GP2. Remember, Force India tester Jules Bianchi and Kevin Magnussen - who will test for McLaren later this year at Yas Marina - are also confirmed there.

13:59 Speaking of FR3.5, the man who was last year's runner-up, Jean-Eric Vergne, comes into the pits in his Toro Rosso. His soft Pirellis look worn, but not blistered.

14:00 Only Button and Rosberg remain on track. Both are on softs.

14:00 Two hours left of the Barcelona test. Of course, we're back here for five more days starting next Thursday.

14:01 Pastor Maldonado and di Resta take to the track to keep them company.

14:03 Rosberg and Maldonado find their way back to the pits, so it's just Button and di Resta; the Scotsman sporting an unsightly periscope gauge on the top of his roll hoop.

14:04 Kobayashi heads out. Still no sign of Mark Webber or Felipe Massa this afternoon.

14:10 Button pits. That's a 13 lap run on soft tyres over. Interesting that the lap times gradually dropped off through the 1m27s and 28s and then suddenly fell into the 30s on lap 11.

14:10 Kovalainen's back out on track.

14:12 Earlier we asked you for your testing surprises on email at Keep them coming in and we'll print the best ones.

14:14 Ntuthuko Hlanguza is surprised at the 'Positive comments for Merc despite their low-key showing so far. Are they really looking good out there?'

Sam Tremayne: "It's always hard to tell exactly given different tyres, fuel and programmes but yes, the Mercedes does look handy."

14:15 George Smith asks if AUTOSPORT live will be at the final test.

Sam Tremayne: "The answer is a resounding yes!"

14:16 Webber makes it onto the track, but his stay is a short one. He returns to the pits after a lap and is instantly wheeled back into the garage.

14:18 Webber was out on a set of softs, and previously used ones if the graining on the rears is anything to go by. Kobayashi and Kovalainen are both out on mediums.

14:18 Maldonado, di Resta and Vergne, meanwhile, are on hards.

14:20 Massa heads out. First time all afternoon. He's currently fifth and completed 56 laps this morning.

14:22 @InsideFerrari Back on track...

14:22 Yep. Thanks for that Ferrari.

14:25 More test surprises now. Hannah Jepson's biggest surprise is 'AUTOSPORT's amazing ability to "accurately" measure banners from the media centre, very impressed.'

That's not all we can measure...

Keep them coming to The best ones will get a mention.

14:26 Webber reappears as Button comes round to start a flying lap.

14:31 Both are on softs. Kobayashi, Massa and Kovalainen are on mediums.

14:31 Vergne has hards, while Rosberg heads out.

14:36 Webber pits.

14:38 Remember what we said about Rosberg earlier? He's just made it onto his 120th lap of the day. Fast closing on Schumacher's distance mark of 24 hours ago.

14:42 You wonder whether or not Rosberg can make it two full race distances today...

14:42 Massa pits with 71 laps to his name today.

14:43 Button, interestingly, is 13 laps into a run on soft rubber.

14:48 So that's Button, Rosberg and Kovalainen on soft tyres, Vergne on hards and Kobayashi on mediums.

14:51 A flurry of cars pit, leaving only a Williams and a Caterham on track. The driver of the latter, Kovalainen, has completed the fewest laps of anybody today. Just 52. That earlier engine change was a factor in that though.

Jenson Button McLaren 2012 Barcelona testing14:54
Jenson Button is currently fourth on the timesheets in his McLaren, less than a second off the pace. Things are closer today time-wise than on previous days; just 1.5s separate the top eight.

14:55 @alex_wurz (watching trackside): Upppsiiii, here comes the Sauber with a sound like a V8 supercar on the pilanespeedlimit, #brokenexhaust

15:00 An hour to go of the Barcelona F1 test. To recap the order, it's Sauber on top with Kamui Kobayashi 0.249s quicker than Pastor Maldonado's Williams. Paul di Resta and Jenson Button next up. Nico Rosberg has completed 125 laps today.

15:05 Massa, di Resta and Webber are the only three drivers on track currently. Three laps down for Webber on this run. Seven each for the other pair.

15:07 Button and Kovalainen are joining them on track now.

15:11 Massa and Webber, by the way, are on mediums.

15:12 ...As Maldonado and Kobayashi head out. That's seven cars on track now.

15:14 Maldonado heads for the pits.

15:16 Medium tyres for Kobayashi and Maldonado. Di Resta, who had been on hards, stops in the pits.

15:16 Kovalainen pits as well, but is replaced on track by Rosberg.

15:18 Marussia is ending its test early after failing to complete a lap today with Charles Pic.

15:19 @Marussia_F1Team As a result of today's problems we've decided to end our test early. The issue was a damaged suspension component to the right rear corner

15:19 @Marussia_F1Team A real shame as we have had such a positive three days of running here. 1577kms in total.

15:20 Kobayashi pits in the Sauber, but returns to the track immediatley.

15:23 Forty minutes left as Vergne heads out.

15:25 Speaking of Marussia, as we just were... See which GP2 team it has signed a technical partnership with, and who is driving for it this year.

15:27 Di Resta heads back out.

15:29 He's done it so quietly, we almost missed it. But Rosberg is now onto his 135th lap. That's a mammoth day of testing for the German. That included a 29-lap run this morning.

15:30 Button and Webber pit as Kovalainen heads out.

15:33 Kovalainen sets a new personal best. 1m26.968s is less than a tenth quicker than his previous mark though and keeps him over 4.6s off the pace.

15:34 He's on softs, as are di Resta, Vergne and Rosberg.

15:34 Medium tyres for Maldonado and Massa, hards for Webber and supersofts for Kobayashi.

15:34 Vergne's practicing pitstops, just as he did in the final hour yesterday. Maldonado is in as well.

15:36 @InsideFerrari This afternoon's work is mainly focused on long runs

15:39 Vergne pits and his crew are down to work again. This time however, he cuts the engine shortly after pulling away. He tried that yesterday during a red flag break.

15:39 Kobayashi pits and then rejoins the circuit.

15:44 Quarter of an hour to go and four drivers on track; Kobayashi, Maldonado, di Resta and Webber.

15:46 Red Flags.

15:48 It's Kobayashi's Sauber. Car is pulled off at the side of the track. Looks like either a technical problem. Could always be out of fuel though. He's pulled off on the inside on the approach to Turn 13.

15:52 The covers are on the C31 as it's strapped to the low-loader.

15:55 Green Flags!

15:55 Five minutes left and Massa, Webber, Vergne and Maldonado are all leaving the pits.

16:02 And that's the end of the session.

16:08 The session actually ended a few seconds early after another red flag for a car out of fuel around the track.

16:10 To recap on the day, Kobayashi was fastest from Maldonado and di Resta. Kovalainen was slowest, but lost time in the morning due to an engine change. Pic didn't complete a lap in the Marussia due to suspension problems.

16:11 Sauber, incidentally, has confirmed that Kobayashi stopping with 15 minutes left - and causing a red flag - was indeed because he was on a dry fuel run.

16:12 Thanks for sticking with us through four gruelling days of testing and for all your emails and tweets - and a special thanks to those who got BOTTAS to be the top trending topic on twitter yesterday in the UK.

16:12 We'll be back in Barcelona next Thursday with wall-to-wall coverage of the final pre-season test of 2012. Of course, that includes AUTOSPORT Live!

16:14 If that's still not enough for you though, you can of course stay logged on to for the rest of night for all the news and analysis of Barcelona Day Four.

16:14 See you all again next week.

P Driver Team Time
1  KobayashiSauber 1m22.312s
2  MaldonadoWilliams 1m22.561s  +0.249
3  Di RestaForce India 1m23.119s  +0.807
4  ButtonMcLaren 1m23.200s  +0.888
5  MassaFerrari 1m23.563s  +1.251
6  WebberRed Bull 1m23.774s  +1.462
7  VergneToro Rosso 1m23.792s  +1.480
8  RosbergMercedes 1m23.843s  +1.531
9  KovalainenCaterham 1m26.968s  +4.656
All timing unofficial. Updated: 16:01 GMT
Mainly sunny High Temp: 16°C / 61°F
Track: Dry
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