Renault driver Fernando Alonso said he was pleased with the team's new Formula One car after its first day of testing.
Fernando Alonso puts the new R25 through its paces
"I have a good first impression - the engine is powerful and the driving position is comfortable," he said.
But cold and windy conditions, and breakdowns, prevented Renault forming a full impression of the car.
"We did not do enough running to have a firm idea of the handling, and our aim is to complete more laps and start learning about the car," Alonso added.
The test comes ahead of the new car's official launch in Monaco on 1 February.
The most obvious change on the R25 over last year's car is a much thinner nose.
Renault's engineering director, Pat Symonds, said he was optimistic the team could improve on their performance in 2004, when they finished third overall behind Ferrari and BAR-Honda.
Symonds said he believed the team had done a good job solving the challenges of the sport's new rules, which have been introduced to lower cornering speeds by reducing aerodynamic downforce.
"This time we started off with about a 25% reduction in downforce and we are nowhere near that now," Symonds said.
"But whether we've done better or worse than other people I'm not sure."
Alonso's team-mate Giancarlo Fisichella, driving last year's R24 car, completed 35 laps of the track working on tyre development, but the unstable conditions and low temperatures prevented him from completing any useful work.
Alonso's best lap time of one minute 11.750 seconds put him third fastest on the day.
He was 0.4secs behind Williams' Antonio Pizzonia and just over 0.1secs slower than Red Bull's Christian Klien.