Lewis Hamilton struggled during practice for the F1 2013 Bahrain Grand Prix on Friday and he conceded afterwards that there is 'a lot of hard work' ahead to try and get his Mercedes properly dialled in.

Hamilton, who has of course got on the podium in the last two races and who was on pole in China, finished the opening practice session down in a lowly 13th place.

While he was quicker in FP2, like most of the other runners, he only just made it inside the top ten on a 1 minute 34.976 seconds.

"We worked as hard as we could today but couldn't quite get the balance of the car to where it needs to be," he lamented. "I had some issues in P1 which we were able to improve for this afternoon so that's a positive, but we need to identify where we are losing time and find more performance.

"We have changed the set-up of the car to what we thought would suit this track but we need to look at that and make sure it is the right direction to go. The heat here is so hard on the tyres so another positive is that we did as many laps as possible to look at long runs and race preparation.

"We're not as far off as we might look today but there is a lot of hard work ahead and it will be a tough battle for us this weekend."

Team-mate Nico Rosberg meanwhile was higher up the leaderboard - setting the third best time in FP1 and the eighth best time in FP2, however, like Hamilton, he also failed to achieve a 'good balance'.

"Our test programme was pretty good today in that we managed to complete everything on our plan. However it's clear that we weren't as strong as on the Fridays of the previous three race weekends," Rosberg stated.

"The car had a lot of understeer and the race will be very tough on the rear tyres. The problem is that when you want to save the rear tyres, you try to set up the car with more understeer and that costs you time over one lap. So it's all about finding the right compromise. We've still got some work to do tonight to find a good balance for tomorrow and the race."

"We haven't yet found the sweet spot of the set-up and that was reflected in the timesheets today," added Mercedes motorsport boss, Toto Wolff.

"It was no secret that we would be facing extremely hot conditions here in Bahrain and that they would make life pretty tricky if you had a car that was not well-balanced. We need to find out why we seem not to be as competitive as we were in the past three races and get the right answers to take a step forward tomorrow relative to our rivals," Wolff summed-up.