Formula 1 returned to action at Barcelona on Tuesday as teams began work in the second and final pre-season test.

Despite only a few days since the first test finished, the updates and developments kept on coming as teams sought out performance gains and worked on solutions to problems that came up last week.

Toro Rosso updates

The STR11 emerged from the pit lane not only in new colours, but with an array of new parts.

The floor ahead of the rear tyre now has 15 smaller slots and the rear dog-legged slot, rather than the two dog-legged slots used in 2015 (see inset below).

Photo by: Giorgio Piola

These slots are used by the teams to manage tyre squirt, the lateral blowing of airflow into the diffuser by the rotation and deformation of the rear tyre.

Changing the airflow characteristics ahead of the tyre will change the shape of the wake it generates.

Having switched to a Ferrari power unit supply from Renault for 2016, the team had a huge amount of work to be ready in time for Melbourne, let alone the tests in Barcelona.

The team will use the 2015-specification Ferrari power unit so it's imperative it hits the ground running and maximises its points haul early on, as the teams running the 2016 power units will continue to receive updates, while it won't.

Photo by: Giorgio Piola

The Y150 Winglet (Monkey Seat, above) has been revised for this test, with a similar treatment employed on the endplates leading edge to what the team has done with the louvres on the main rear wing assembly.

McLaren sidepods

Photo by: Giorgio Piola

McLaren revised its sidepod geometry today, increasing the size of the rear cooling outlets.

It is understood this is in line with changes made by Honda to the power unit, which require a little additional cooling for performance reasons.

Even though the tweaks appear to be a move away from the 'size-zero' philosophy – with the additional bodywork requirements meaning the outlet extrudes upward rather than into the coke-bottle region – maybe the team has found a way of doing this without compromising performance.

Photo by: XPB Images

This follows the extensive tests conducted by the team last week (above), using kiel probe arrays to measure airflow over the sidepod.

Mercedes’ new rear wing

Photo by: Giorgio Piola

Mercedes continue to pile on the pressure, having concentrated on updates at the front of the W07 during the first week of tests, they've mounted a totally revised rear wing assembly on day one of the second test.

The new wing features two much taller leading-edge tyre wake slots, rather than the short singular slot. You'll also note that they have carefully shaped the endplate just under the flapped section to define the flow structures.

The cutout behind the flapped region has also been revised as the team explore ways of changing how the tip vortex forms, as this can be damaging to performance.

Meanwhile, the serrations used by Mercedes, rather than vertical strakes used by other teams, to entice upwash, have been increased in frequency from two to three.

The flaps have also undergone some changes from the first test specification, with the upper flap now featuring a straight outer edge, whilst the centreline V groove has been shrunk too (marked in yellow). Meanwhile, the centreline dip has been inverted (marked in purple).

It is our understanding that the specification used in week one is more of a lower-downforce configuration, and this new specification is the first look at what we can expect to see at some of the higher-downforce tracks.

Mercedes complimented this higher downforce rear wing configuration with a 2 slot / three tier Y150 Winglet (Monkey Seat, below) during the afternoon session, which should provide more stability for the drivers.

Photo by: Giorgio Piola

Mercedes tape

Mercedes showed on Tuesday it is leaving no stone unturned in its quest to understand the aerodynamic performance of its car.

During last week's first test, the team's behaviour in sometimes hiding its car behind screens on its return to the pits had intrigued many observers.

However, the real reason emerged on the start of the second test – as these exclusive photographs below of what the team was up to show.

As you can see, mechanics were seen removing a section of serrated tape from the rear of the flap at the top of the rear wing – so the team can conduct back-to-back tests.

Photo by: Giorgio Piola

The effect of the tape on aerodynamic performance will be minimal, but by re-energising the flow with this tape, it may be enough.

Photo by: Giorgio Piola

And having first experimented with this solution at last year's Abu Dhabi test, it shows the lengths Mercedes is going to in extracting performance from its W07.

Photo by: Giorgio Piola

Ferrari aero tweaks

This morning Ferrari, not for the first time in recent history, added a small canard to the front wing endplate (highlighted in light blue in the inset, below).

This is a control device, changing the pressure gradient and helping to shape the streamwise vortex that controls the front tyres’ wake.

Photo by: Giorgio Piola

This picture (below) of the diffuser affords us a good view of the additional fin (highlighted in green in the inset) added by Ferrari at the last test.

You can see that there is already a stack of winglets mounted ahead of the diffuser, as used by the team last year, with those and then new winglet maximising the performance of the outer section.