Sebastian Vettel says Red Bull is still struggling to understand the disparity in performance between his Bahrain victory and his sixth-place finish at Catalunya.
After a solitary podium in the opening three races, Vettel scored a clean sweep of pole, victory and fastest lap at Bahrain, indicating that the squad had rediscovered its 2011 winning touch.
He was therefore one of the pre-race favourites heading into Barcelona, a circuit Red Bull had dominated on in 2010 and '11, but suffered a difficult weekend, qualifying seventh and eventually salvaging sixth following a late charge on fresher rubber.
Vettel says the team is still trying to understand exactly where it lost performance.
"For the first time this year we had a clean weekend in Bahrain, a weekend where I was happy the balance of the car and we had a good result," Vettel said. "Coming to Barcelona we were hoping for a similar result but it looks like we are not that competitive and we have tried to understand why that was.
"It is not as if we had a clear answer. We have some ideas - I was pretty happy in practice on Friday and Saturday morning and coming into qualifying we just didn't seem to make the step that the majority of the grid made.
"It is difficult to draw a full conclusion because when you start further back you are likely to be in traffic for the first part of the race, but the gap to the front was too big - our maximum position was P5, it is not as if we could have argued over the first four places.
"At the moment and it is difficult for us to understand why sometimes we are quick and sometimes we are slow and why the pace changes, [but] it is not only us struggling a bit at the moment."
Asked about the influence Pirelli's 2012 compounds were having on the racing order, Vettel admitted they had clouded the picture but said he was still confident the best teams would come to the fore as the season progresses.
"If you look at an average of the first five races, I still believe that you have the drivers and the teams at the front which deserve to be [there]," said Vettel.
"We have seen different people winning, five different teams and five different drivers so I think on average through a season with 20 races it is not right to say that the winner will be lucky.
"It is still in some ways the beginning of the season and I think the tyres are extremely difficult to understand."