All change in Barcelona: Your guide to what's changed on the cars this weekend

Who's changed what and where - and why....

McLaren
Bereft of competitive aerodynamic downforce in the opening flyaways, the MP4-29 has been rearmed with a series of tweaks this weekend. The car's rear-end has been repackaged, with an extra cut made to the bodywork in order to house a revised suspension arm, while the front-wing features a series of fresh endplates. Of particular encouragement to the team, after their struggles to understand the team's behaviour in Bahrain and China, was the car's consistency during Practice One in Barcelona with Jenson Button's anguished report of understeer actually greeted with enthusiasm by his pitwall as it dovetailed with their predictions. "It's encouraging to see that the package has been a useful step," said Eric Boullier. "It seems to have corrected some of the problems that affected us in China last month, but we're still only taking the first steps on a long journey back to the front." Williams
Another team putting their car on a diet over the last three weeks. Somewhat under the radar, the team have tightened the FW36 for Barcelona, with the tweaks most noticeable around the shrink-wrapped bodywork housing the exhaust. "The parts we brought are working as expected or even better, which is key at a track like Barcelona where everyone is trying to find more downforce," confirmed Rob Smedley afterwards. Toro Rosso
Never particularly keen on public pronouncements, Toro Rosso kept their cards very close to their chest heading to Barcelona but they are nonetheless running with a revised rear-wing, rear wing endplates and a new diffuser this weekend. A new chassis for Jean-Eric Vergne was spotted arriving at the circuit late on Thursday night - but, true to form, the team have yet to divulge whether it was a brand-new chassis or a car that, a la Vettel, was previously used during winter testing. Lotus
Having gone from the back of the grid to Q3 during the course of the opening flyaways, Lotus are eyeing their first points of 2014 in Spain and have brought a number of updates to help them achieve that aim. The most eye-catching change to the E22 is a tower block of deflectors on the inside of their asymmetrical nosecone, while the Enstone team have also been busy working on new cooling and bodywork packages, including rear-wing tweaks, as well as engine mapping upgrades. Sauber
Having failed to trouble the scorers in the first four races of the year, Sauber have introduced a comprehensive range of upgrades this weekend. Their car now features a modified rear and front-wing, along with a new floor, and updated sidepods. More dramatically, a brand-new chassis has been introduced which is reputedly 15kg lighter than the previous model - welcome relief to Adrian Sutil, in particular, after the German revealed he went without food for two days at the start of the season amid concerns that, as one of the grid's taller drivers, he was being penalised. Marussia
Striving to stay ahead of Caterham at the back of the grid, Marussia ran a range of small, but seemingly useful, new parts in Practice One with changes at both the front and rear of their car. But just the one: while Jules Bianchi debuted the upgrades, team-mate Max Chilton ran in an unmodified charger in order for the team to evaluate the effect of the new parts. Chilton and Bianchi will then swap roles on Saturday, starting in P3. Caterham
The CT05 features what team boss Cyril Abiteboul has described as "a typical Barcelona package" with revisions to both the car's front and rear wing, and floor. However, after their two cars propped up the timesheet on Friday, Abiteboul admitted the revisions were "not working great" as yet.