Mercedes driver Nico Rosberg was looking very happy with things at the end of his stint in the new F1 W04 during pre-season testing at the Circuit de Catalunya just outside Barcelona, Spain.

"I am pleased, it is a good start at the moment," the German driver told Sky Sports News on Thursday. "The car feels good and the short runs, long runs, everything is looking okay."

Rosberg went further and also gave it a favourable rating in comparison to last year's model, which went on to deliver Mercedes its first Grand Prix victory since Juan Manuel Fangio in 1955 by claiming the chequered flag in China.

Related Articles

"It is definitely progress from last year," he said. "For sure we will be closer to the top guys. That is important to be heading in the right direction."

After that early success in 2012 the team struggled to match the improvements posted by its main rivals including Red Bull, McLaren and Ferrari. Rosberg is under no illusion that they must ensure that the same loss of momentum doesn't happen this season as well.

"What is also looking good is our development rate at the moment, it is quite a decent rate and that was our weakness last year," he admitted. "So that is going in the right direction too. All these factors are going well at the moment but we are not quite there yet.

"The team has done a really good job over the winter and it looks like all their hard work and effort has definitely been worthwhile," he added. "The car is a pleasure to drive as the balance is good."

The new car did suffer an early technical failure at Jerez, and while such things are to be expected in testing the driver is all too aware that reliability could make or break his hopes in the forthcoming season.

"Obviously reliability is something we need to improve, we had a few issues but nothing major," he admitted.

"In general, I'm pleased with what we've achieved this week," Rosberg summed up. "I feel more comfortable in the car and the balance is quite good, but we still need to work in a number of areas. That's why I'm looking forward to testing next week and to see what progress we can make."

Rosberg's new team mate Lewis Hamilton will take over the car for the fourth and final day of this current Barcelona test session. After his most recent runs on Wednesday, the former world champion was also expressing positive thoughts about his new hardware for 2013.

"It's going in the right direction.," Hamilton said. "We're not focusing on anyone else; we're just looking at our programme to try to make steps forward with the degradation and set-up ... All the tyres are having degradation so looking after them is not that easy, but that's normal."

Hamilton was second-fastest on Wednesday to the man who replaced him at McLaren, Sergio Perez - although the Mexican was on softer tyres to Hamilton, making the comparison an inexact one at best.

Rosberg finished the Thursday session in fourth place behind Ferrari's Fernando Alonso, Sauber's Nico Hulkenberg and Lotus driver Romain Grosjean, having put in 108 laps of the 2.892-mile, 16-turn circuit.