Rosberg said the obvious key moment of the race was the start, and he needed to make gains in that area if he wanted to challenge his teammate and new championship leader, Lewis Hamilton.
He also admitted he needs to work on his braking, especially before the Grand Prix of Monaco scheduled next week.
"I had a productive day of testing in Barcelona where we made some good progress with braking and starts: two areas that I feel are costing me time at the moment,” Rosberg said in a Monaco GP team preview.
"Hopefully that will give me the extra edge next weekend. It should be an exciting weekend and I can't wait to get started."
|Nico Rosbeg, Mercedes AMG (Photo: Mercedes)|
The areas Rosberg identified will both be crucial on the streets of Monte Carlo, where the driver starting on pole has gone on to win all-but one of the races in the last decade.
“My race start at the Spanish Grand Prix unfortunately was poor. It's a bit of a weakness that we have at the moment, just inconsistent and now I've had a couple of bad starts in a row - actually three bad starts in the races.
"And that's costly, you know? Because, always losing out at the start, that's not good, [I] need to work on that,” Rosberg admitted.