Nico Rosberg is adamant Mercedes are moving forward and have resolved their rear tyres issues from last season.
Mercedes' efforts in 2012 were at times undone as their rear tyres lit up, prompting the team to pit earlier than their rivals.
This year, though, Rosberg believes the team has found a solution in their W04.
"The car is definitely a big step forward," he told Formula1.com. "It feels very nice to drive with a good balance. It is a massive step.
"Take the rear. We had massive problems with tyre heating and losing grip and all that. That seems to be history now. And that is really a massive change."
Asked whether Merc have taken a step closer to the front, Rosberg said: "I can feel it, but you can also see the progress in the factory. It is faster, working better, taking much less time to turn things around.
"Of course what is visible immediately is more people are working towards our goal."
Mercedes had a problematic start to testing, losing almost two full days running at Jerez. However, at Barcelona the Brackley-based squad appeared to have ironed out their issues.
"That's why we are testing - to eliminate them," Rosberg said. "I was not worried at all and I was much more enthusiastic about the speed that we have."
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