McLaren CEO Martin Whitmarsh has said that while the team is confident they have made a lot of improvements during the recent break, he remains cautious as it is difficult to judge what steps their rivals have made.

Speaking ahead of the Spanish Grand Prix next weekend, the fourth round in the 2008 World Championship, Whitmarsh added that they won't get a clear indication of the pecking order until practice this coming Friday.

With the Bahrain weekend not having gone especially well though, Lewis Hamilton and Heikki Kovalainen will both be hoping the modifications have the desired effect.

"The Spanish Grand Prix sees us entering the European season and McLaren Mercedes, along with all the other teams, will be in Barcelona with significant upgrade packages on the cars," said Whitmarsh.

"The cars remain relatively consistent over the course of the fly away races and this race weekend is the first opportunity to understand how we have moved forward with performance and developed the MP4-23 in comparison with our primary competitors.

"We are confident that we have improved the performance of the car, but this week's test was not an accurate indicator of performance, so we will need to wait for the race to establish how the MP4-23 will fair."

Asked what areas the team have been focusing on in the build up to the race, Whitmarsh added that they have tried to cure a number of 'vices' highlighted by the opening three rounds.

"The emphasis has been on the aerodynamic performance, developing downforce, balance and aerodynamic efficiency. In parallel we have developed the suspension systems and the chassis," he explained.

"We have come away from three races with no testing where inevitably we discovered vices that were not analysed before the start of the season.

"The car was new to all of us when we were testing in the winter, it is now an established package and like any car it has its strengths and weaknesses.

"There is a very comprehensive package of components and systems that were fitted to the car at the test, hopefully to build on the strengths and reduce the weaknesses, but we will see how far forward we have been able to take the car.

"As always with these test sessions there are a range of variables such as tyre specifications and fuel loads. In addition it was decided by the teams and Bridgestone that we needed to spend some time developing the 2009 slick tyre.

"In order to test those in a representative manner you have to estimate the level of downforce that will be available under the 2009 aerodynamic regulations, and we do not know what the other teams are doing in that regard.

"Whilst we confined this testing to one day, this was not the case across all the teams - which led to a range of times during the whole week. As a result it is very difficult to make an accurate assessment as to where everyone is."

Crash / Eurosport