Nico Rosberg played down his chart-topping form in the second free practice session in Bahrain, cautioning that Mercedes' tire-overheating issues are "probably the worst they have been."
Mercedes struggled with both tire degradation and issues switching the Pirellis on in the first two races of 2012, but appeared to make a huge leap in China as Rosberg took a commanding maiden Formula 1 victory from pole position.
The German built on that by setting the fastest time in practice two at Sakhir, but he was quick to downplay the significance of his lower fuel run.
"It has been a good day – it's nice to be quickest on low fuel, but as we know anyway the car is good on lower fuel," he explained. "In general, conditions are probably the worst they have been here with the tires overheating.
"We learned a lot and we are looking much better than maybe we would have thought. But we need to see where we are. We are having to make changes because out there it's very unusual - conditions are very tough."
His Mercedes stablemate Michael Schumacher said that issues with the tires would improve, and were at least shared by everyone along the pitlane.
"The tires are a big issue because they are just going away like nothing but it's the same problem for everybody," he added. "It will improve a bit. Let's see how many tires we are going to need in the race."