The young German was joined on track by team mate Kazuki Nakjima, who finished second, albeit almost two seconds down on Rosberg. The pair covered over 150 laps as they continued the British teams development programme for the FW30, concentrating on set-up runs and endurance work.
Third quickest was Mark Webber for Red Bull. Webber covered just 27 laps during the session while his team mate David Coulthard, fifth, completed 23. With the team choosing to run so few laps the pair concentrated on practice starts. Coulthard added an element of excitement after briefly making contact with the wall at Turns 7 and 8 but the minor damage to his RB4 was quickly fixed.
Splitting the two Red Bull drivers was Fernando Alonso for Renault in fourth. Alonso was joined by team mate Nelson Piquet Jr, who ended the day in seventh. Both were restricted to limited running, completing 16 and 8 laps respectively.
“It was a day disrupted by the weather and so we did not learn much at all really,” explained Christian Silk, Renault's chief test engineer. “When you have days like this you just have to adapt the programme as best you can, and so we made the most of the rain by completing some wet weather running just to check the balance of the cars and to carry out basic system checks.”
Jarno Trulli finished sixth fastest for Toyota as he continued the Japanese teams pre-season programme. Although the squad had intended to carry out comparative work on the TF108s new aerodynamics package, the unsettled conditions limited Trullis running to 57 laps.
Even so, the Italians day was more productive than that of team tester Kamui Kobayashi, who completed just one installation lap. Kobayashi spent the day in the Toyota garage waiting, fruitlessly, for the weather to improve.
“That was a short days work for me,” said the Jaapnese driver. “We have limits on testing mileage so it was decided that we could not use up laps in conditions like these. Thats the way testing goes sometimes but at least I have been able to recover fully after a long trip from Indonesia yesterday.”
Testing will continue at the Circuit de Catalunya on Wednesday, when both McLaren - who opted not to run on Tuesday due to the weather - and Ferrari are expected to join proceedings.
Elsewhere on Tuesday, BMW Sauber continued their programme of testing at Valencia. The German-Swiss team were, however, as hampered by the weather as their colleagues in Barcelona and race drivers Robert Kubica and Nick Heidfeld covered under 30 laps in total, collecting data in the F1.08 whilst running on wet tyres. The pair will continue to test at the Spanish circuit on Wednesday.
Unofficial Tuesday times from Barcelona:
1. Nico Rosberg, Williams, 1:30.675
2. Kazuki Nakajima, Williams, 1:32.370
3. Mark Webber, Red Bull, 1:32.599
4. Fernando Alonso, Renault, 1:32.820
5. David Coulthard, Red Bull, 1:32.924
6. Jarno Trulli, Toyota, 1:33.283
7. Nelson Piquet Jr, Renault, 1:40.073
8. Kamui Kobayashi, Toyota, no time
