The test conducted by Pirelli and Mercedes was indeed illegal in accordance with the Formula One / FIA's Sporting Regulations with in-season testing outlawed.
The use of Mercedes W04 in conjunction with Pirelli constitutes in season testing but both parties argued they had authorization test with the FIA.
The FIA clarified its position, stating that certain criteria must be met in order for the test to occur. This criteria centered around the unanimous support of the teams in using a current car. The FIA were not satisfied this caveat was fulfilled by Pirelli and so the test was essentially ran without their consent.
The largest question is, how much did Mercedes learn from the test? However I think in order to answer this we must also consider some other factors...
The tyres used in Barcelona at the test in question were prototypes used to assess their initial thoughts for 2014. Pirelli had around 12 different tyres to test over a 1000km distance. Undoubtedly an array of constructions and compounds were reviewed giving Pirelli data to move forward with their designs for 2014.
Why did Pirelli feel the need to test with a representative car (2012/2013)? Well the problem for Pirelli is their current test car is a Renault R31 from 2010, the Italian tyre manufacturer claim that their car is now impractical for testing tyres as it doesn't represent the current level of downforce seen by the teams. Furthermore their driver lineup doesn't drive the cars on a consistent basis and will inevitably spend a proportion of their time in the car acclimatizing.
Pirelli have also completed a tyre test with Ferrari and Felipe Massa earlier this season utilizing their 2011 challenger the F150. As the F150 isn't seen as representative the test doesn't come under the scrutiny of the FIA / Sporting Regulations but it further enforces Pirelli's need to test their product. The test was rumored to have been conducted in order to assess a new tyre choice for 2013 with Pirelli unhappy with both the teams criticism of their product this season and concerns over the safety of the tyres with delaminations seen in the early races. Following on from an exchange with Paul Hembrey of Pirelli though he tells me that although other things were tested their intent was to create a procedure for evaluating flat spotting on the 2014 tyres (under braking).
The changes afoot in 2014 are monumental with challenges being faced in terms of both engines and aerodynamics. I've looked at both these topics in more detail already:
Aero - http://somersf1.blogspot.co.
Power Units -http://somersf1.blogspot.com/
In short aerodynamically the cars will be robbed of the Beam Wing at the rear of the car which aids in the overall airflow structure at the rear of the car, reducing the effectiveness of the Rear Wing and Diffuser. The narrowing of the Front Wing raises new challenges for the designers in the way they structure the airflow around the front tyres and onwards along the rest of the car.
The new Power Units power curve will be substantially steeper with roughly the same power available but with a much smaller rev band (18,000rpm reduced to 15,000rpm but with the fuel flow restriction above 10,500rpm it's more likely we'll see the units only rev just beyond that)
This puts an even larger importance on the design characteristics of 2014's tyre, especially with pressure still on the tyre manufacturer to create a situation where teams stop around 3 times.
So Pirelli are damned if they do and damned if they don't but that's nothing new. As Paul Hembery has stated before Pirelli are more than happy to create 'Concrete Tyres' (tyres that can last a whole race) but that's not their brief from the FIA.
So what happened at the last rule change? Well let's look back to 2009...
Bridgestone had been supplying grooved tyres to F1 for a number years, with the FIA introducing new rules in order to encourage more overtaking they also asked Bridgestone to bring back Slick tyres. This would add an element of mechanical grip that was lost with the grooved tyres giving the driver more feel in the corners.
The idea worked to some extent but it needed tweaking. With Bridgestone questioning their involvement / relevance in F1 with slick tyres they departed the sport at the end of 2010.
Pirelli's entrance into the sport bought with it an air of transparency, in the Bridgstone era compound choices were shielded from public view and tyres simply denoted as Prime and Option (Hard and Soft).
This regime was a carry over from the pre 2009 grooved tyre rules and something Pirelli shook up when they entered in 2011. Offering up 4 slick tyre compounds for that season (Hard,Medium,Soft and Super Soft) the tyre manufacturer would select 2 of them for each race to feature as the Prime and Option tyres.
This approach although commendable in my opinion for its transparency has sometimes seen Pirelli come in for flack that Bridgestone perhaps shielded itself from by not showing its entire hand.
Tyres have been a matter of complaint throughout Pirellis tenure in F1 with teams taking umbridge to the designs used by the Italian manufacturer.
In 2012 we saw an incredible start to the season with 7 winners from 7 races as teams grappled to understand the way in which the tyres came upto and stayed in their operating window. Stiff sidewalls meant heating the tyres through conventional methods were restrictive, meanwhile the stiff sidewall lead to the shoulders wearing quicker than the rest of the tread platform with the central section often showing very little signs of wear when taken off the car.
For 2013 Pirelli looked to address this scenario bringing thermal degradation to the fore. However the teams have this season struggled to adapt aerodynamically as the tyres more flexible Sidwall not only effect the mechanical grip but organically effect the aerodynamic platform as the car brakes, accelerates and corners. I've explained this in more detail here:
The reason I raise the point once more though is that F1 teams forever look for the opportunity to discredit or take an advantage from their opponents. Earlier in the season some teams fired a shot across the bow of Lotus claiming that the use of their R31 by Pirelli had therefore inherently favoured the Enstone based team gifting them with a car that was much easier on its tyres.
How can we expect a tyre manufacturer to influence the amount of pitstops in a race when they don't have access to a relevant car?
Should the FIA relax their brief on Pirelli for 2014? with the huge challenges already faced by the teams making the design more complex by virtue of tyre dynamics could be disastrous.
Do the FIA need to re-assess their approach to two stage tyre usage and/or the qualifying format?
Has Formula One got to a point where restricted in-season testing has become acceptable?
The resounding question however is how much did Mercedes learn from their time in Barcelona? I understand them using their race drivers as with only 1000km and a packed programme it's better that a driver comfortable in their surroundings is better equipped than a test driver like Sam Bird or Brendon Hartley who in this era of F1 spend time in the Simulator but very little in the car.
I'm certainly not convinced that the time spent in Barcelona by Mercedes has gone any way toward rectifying their tyre degradation issues. The team haven't done so in the 2 and a bit years since Pirelli have been in the sport and so one extra test won't be that secret elixir they've been missing.
Of course many looked at Monaco as a sign the team had turned a corner but If we look back to 2012 bar his grid penalty, Schumacher would have been on pole. Therefore it should have been no shock that the 2 Mercedes drivers started from 1-2 on the grid in the Principality.
I won't go as far to say that Mercedes learnt nothing and undoubtedly time in the car for the race drivers aids in their approach. Solving their 2013 degradation issues when testing prototype tyres of unknown construction and compounds would be difficult but not entirely improbable too, so the jury is still out...
The team state their programme was controlled by Pirelli and no updates were tested ahead of Monaco which in reality without test equipment on the car (pitot tubes, flo-viz etc) it would be difficult to correlate any worthwhile data.
The biggest issue I have with the punishment levied on Mercedes at the International Tribunal though is disadvantage the other race drivers now face. Both Hamilton and Rosberg drove during those few days of testing in Barcelona giving them time in the car that the other race drivers simply cannot get this season.
By banning Mercedes from the Young Driver Test their race drivers have gained an advantage with the other teams only able to run their support drivers.
Of course if Mercedes didn't run upgrades to the W04 during the test then the teams running at the YDT are able to gain an aerodynamic advantage using their drivers to assess any future packages.
I mean no disrespect in this next comment but a race driver has a perspective that the support drivers cannot offer, they don't usually drive the car in a competitive manner and so are less accomplished to give opinions on upgrades. Of course the driver can be given the previous specification car as a reference to work from but it's never quite the same.
I'd argue that should any of the teams decide to take their race drivers to the Young Drivers Test it should be overlooked by the FIA for the sake of parity.
I think the lesson that should be taken away from the whole debacle is that the stranglehold on track testing needs to be reviewed. The cost reductions that were intended by the introduction of the in-season testing haven't really come to fruition. Formula One teams will always find other areas in which to spend cash and gain an advantage over their rivals. It can come from various avenues: CFD, Wind Tunnel, test equipment /rigs or even just streamlining their processes but one things for certain those that spend money will nearly always see a return for their investment.
The re-introduction of in-season testing in 2012 (Mugello) offered no real benefit to the likes of Red Bull & Lotus teams that have seemingly fully embraced the testing restricted regulations. Ferrari however are an advocate for a return to in-season testing and reveled in the opportunity to test at Mugello.
The largest problem with the Mugello test of 2012 was one of cost. Many teams saw it as an expense they didn't need as they for the last few years had found solace in the restrictions.
The FIA, teams and FOM need to strike a balance that reintroduces in-season testing without the costs spiraling beyond the control of some of the smaller teams. The likes of Caterham and Marussia may even make strides with a return to track testing as it aids in correlating the information seen in CFD, Wind Tunnel and test rigs...
As we stand on the precipice of another huge rule change, decisions made now could shape the sport for years to come, I only hope that the testing rules are adapted to better suit the economic and technological time frame we currently sit within.
The problem as always is that everyone is in it for theirselves and a resolution that fits the sport as a whole can never be found.
Egos aside with a Concorde Agreement still not in place the sport and it's rules could be rejuvenated if all sides can look at the bigger picture. Come on F1 wake up and make the Sport even better for the fans!