Hot conditions persisted at the Spanish circuit and Webber was able to complete 85 laps in total. The Australians programme focused on aero development work and suspension changes but the squad also carried out some 2009 tyre tests. Team mate David Coulthard will take over driving duties on Friday.
“Weve had a pretty good two days here,” said Webber. “The car ran pretty reliably and weve clocked up some good mileage. Today we were mostly getting ready for Budapest, as well as looking at developments for a little later in the season. Yesterday we were focusing more on ‘09, and it was quite a challenging day. Today was better in terms of what we learned, mechanically and aerodynamically. Its been a hot week for the guys working here and theyve done a good job.”
Piquet was equally productive, completing 95 laps, as he spent the day evaluating Bridgestone's 2009 slick tyres. Raikkonen, meanwhile, focused his attention on preparations for the forthcoming Hungarian race, although he did switch to the slick rubber later in the day. He covered 84 laps and will hand over the F2008 to team mate Felipe Massa on Friday.
"We have done many tests over these two days to try and understand what happened at Hockenheim and now we have a clearer idea on this matter,” said the Finn. "Today, the car had improved compared to yesterday and we hope to be ready for the next rounds. Our opponents are very strong, but there is still a long way to go in this championship and all the time to recover, given that in Formula One things can change a lot in no time at all."
Fourth fastest was tester Vitantonio Liuzzi for Force India. Liuzzi continued to evaluate the team's new seamless shift gearbox, alongside some aerodynamic work and brake testing. In the afternoon, the squad also tested Bridgestone's 2009 slick tyres. He covered 86 laps in total. Giancarlo Fisichella had been scheduled to take over the VJM01 on Friday, but with the Italian currently suffering from a minor virus, team mate Adrian Sutil will be in charge of driving duties.
McLaren tester Pedro de la Rosa ended the day in fifth. With an oil leak and subsequent engine change limiting his running, De la Rosa only managed to complete 39 laps. He will hand over the MP4-23 to Heikki Kovalainen for the final day of the test.
Toro Rossos Sebastian Bourdais, meanwhile, covered 77 laps in the STR3, as he assessed a new wing the team plan to use during the Belgian race weekend in September. Bourdais finished just ahead of Williams Kazuki Nakajima, who completed 88 laps in the FW30.
Timo Glock was back in action for Toyota following his high-speed crash during the German Grand Prix. Glock was eighth quickest and covered 78 laps, before an issue with the TF108s fuel system ended his day prematurely. Third driver Kamui Kobayashi will take charge of testing duties for the Japanese team on Friday.
"It was good to get back in the car and that was a positive day's testing for us,” said Glock. “We pushed hard in the morning and we were able to get through most of our plan for the day before lunch. That was useful because in the afternoon here it gets too hot and the track is just too slow to get a clear picture out of the car. Late on we had a fuel system issue but we had already gathered the data we wanted. The main thing is that I've made a full recovery from my accident on Sunday and I feel fine."
Rubens Barrichello was ninth quickest for Honda. Barrichello continued to evaluate the teams new rear suspension for the RA108 and covered 68 laps. Completing the line-up on Thursday was BMW Saubers Nick Heideld, who completed 97 laps in the F1.08. Heidfeld concentrated on development work with the 2009 slick tyres.
Testing continues at Jerez on Friday.
Unofficial Thursday times from Jerez:
1. Mark Webber, Red Bull, 1:19.176
2. Nelson Piquet, Renault, 1:19.334
3. Kimi Raikkonen, Ferrari, 1:19.434
4. Vitantonio Liuzzi, Force India, 1:19.544
5. Pedro de la Rosa, McLaren, 1:19.850
6. Sebastien Bourdais, Toro Rosso, 1:20.029
7. Kazuki Nakajima, Williams, 1:20.097
8. Timo Glock, Toyota, 1:20.421
9. Rubens Barrichello, Honda, 1:20.614
10. Nick Heidfeld, BMW Sauber, 1:20.896