Alex Wurz, enjoying his first day in the new WilliamsF1 FW28, topped the timesheets on the first day of testing at Jerez.

The Austrian was joined by WilliamsF1 2006 race driver Nico Rosberg, as the Grove outfit showed definite signs of improvement.

"Today, I drove the FW28 for the first time," said Wurz. "I soon familiarised myself with the new characteristics, which my lap times showed, and I feel quite comfortable with it already. Nevertheless, I am a perfectionist and that means that we need to do some more work to extract more out of our package. The basic elements are there, now it's just a race against time to optimise everything before the season opener. We'll be pushing flat out!"

"Today, Nico and Alex started off the Jerez test, both in FW28s," added Sam Michaels. "The drivers worked on mechanical set-up all day and found some interesting directions to pursue for the rest of the test. Mark and Nico will be driving tomorrow and will each spend half the day carrying out pit-stop practices with the race team crew."

Honda drivers Jenson Button and Rubens Barrichello were second and third quickest, both drivers spending the morning session setting up their cars, as the circuit had quite low grip following two weeks of MotoGP testing.

In the afternoon, the Englishman ran through a tyre evaluation programme over longer runs, alongside an aero evaluation, while the Brazilian spent the afternoon working through a race simulation exercise followed by a short tyre evaluation.

Both drivers will remain in their respective cars for tomorrow.

Toyota started this week's test with third driver Ricardo Zonta joined by test driver Olivier Panis. The team furthered its Bridgestone tyre test programme and will have race drivers Jarno Trulli and Ralf Schumacher on hand to continue work over the next two days.

With the first race in Bahrain just over a month away, the testing is all-important to the team's performance in the first three 'flyaway' races in March and early April.

"We did some long runs and it was a successful day in terms of learning more about the car," said Zonta, who worked on suspension set-ups as well as tyre evaluation. "We tried some different dampers and made good progress, so that was satisfying. The rear of the car felt almost perfect and we have some other interesting developments which the race drivers can try tomorrow."

"This morning I evaluated some tyres that the team tried in Valencia at the last test," added Panis. "They look pretty promising and I am happy about everything. I think Bridgestone has made a good step up but let's wait until we can evaluate the whole package over the remaining tests, when we will also have the new aerodynamic parts."

Also on duty was Midland F1, with Tiago Monteiro at the wheel of the (Jordan) EJ15B and Christijan Albers at the wheel of the new M16.

The Portuguese driver continued to put mileage on 2006 components, in addition to working on software development and some aerodynamic testing and set-up development.

Meanwhile, it was a positive first day for the new M16 chassis as the team ran through a number of routine 'new car' systems checks and began familiarising itself with the set-up options available.