Nico Rosberg admitted that tire degradation is worse today than it was during preseason testing after what he and teammate Michael Schumacher both described as a "challenging" Friday for Mercedes.
Rosberg ended the day third fastest, 0.372sec off pacesetter Jenson Button, but underlined that tire management will be the deciding factor in Sunday's race.
"It was very different to winter testing and a lot tougher on the tires," said Rosberg after practice. "It has been a very challenging day first of all to see how to get the car right for qualifying and especially how to get it right for the race.
"I don't know where we are on tire wear. We will have to look through the data now. tire management is going to be crucial here."
Schumacher, who has criticized the Pirelli rubber in recent weeks, agreed that the Pirelli rubber is the main challenge faced by the team. He ended the day eighth fastest, setting a best time 0.681sec off the pace but emphasized that his main focus was on race pace rather than qualifying speed.
"That's a challenge," he said of tire degradation. "We have to find out more and analyze it too see what we did compared to the other guys. We have four of them [tires] each time we go out and it's the same for everybody."