- Williams unveiled new FW35 at Barcelona Tuesday
- Pastor Maldonado took the new car for a spin around Circuit de Catalunya
- Williams confident new car will help team compete at the front end of the grid
- Mercedes star Nico Rosberg the fastest man on the track on first day of testing
Williams unveiled its new car for the 2013 season on the first day of testing at Barcelona Tuesday with renewed ambition following a complete transformation of last season's vehicle.
The Renault-powered FW35 "is an evolution of the FW34 of 2012, it's better and more refined, with more than 80 percent new parts," Williams' technical director Mike Coughlan told reporters.
Venezuela's Pastor Maldonado gave the team its first win in seven-and-a-half years when he triumphed at last season's Spanish Grand Prix.
Maldonado, who is entering his third season with Williams, will be joined in the paddock by 23-year-old Finn Valtteri Bottas, who replaced Bruno Senna.
Team owner Frank Williams is confident that his team will be ready to compete at the front of the grid when the season starts in Australia on March 17.
Williams told reporters: "A talented group of people with lots of imagination worked hard to produce the FW35.
"We believe it represents a step forward to last year's car which was already very competitive."
Meanwhile, Mercedes' Nico Rosberg clocked the fastest time of the day at 1 minute 22.616 seconds.
The German edged out Lotus's Kimi Raikkonen with Ferrari's Fernando Alonso finishing third fastest.
Alonso, who is chasing a third world title, recorded a fastest time of 1 minute 22.952 seconds.
Triple world champion Sebastian Vettel finished three tenths of a second slower than Rosberg after leading the time charts following the morning session.
Rosberg told the Mercedes website: "We had a mixed day today with some laps lost this morning. However we were able to work through a good program this afternoon and, of course, it's always nice to be quickest at the end of the day.
"In general, I feel happy and comfortable in the car and it feels better than the last time we were here at this track. There is still some work to be done on tire degradation and our program this afternoon was helpful in understanding that."