On the fourth day of a 'difficult' test for BAR at Jerez, Jenson Button sent out a clear warning to the Brackley team's rivals, and critics, by posting the fastest time of the year, missing out on the unofficial lap record by a mere 0.066s.

Button spent the day running through an aerodynamic evaluation alongside a tyre programme, completing 129 laps and running the latest specification Honda engine to its target mileage.

Enrique Bernoldi joined the test, driving an 006. The Brazilian ran through an aerodynamic programme before completing long tyre runs, completing a total of 122 laps.

After a frustrating start to the week's programme, the team was buoyed by signs of the car's true potential.

The vast majority of the team's testing to date has focused on reliability and understanding how the tyres perform under the new sporting regulations. Today, for the first time, the team has explored the car's ultimate performance on lower fuel levels. The signs were clearly very encouraging.

Juan Pablo Montoya was second quickest, albeit 0.518s off the Englishman's pace. The Colombian was joined by teammate Kimi Raikkonen who had to sit out Thursday as the team waited for a replacement for a damaged suspension part.

Both drivers' programmes focussed on simulated qualifying runs in the morning and endurance runs in the afternoon.

Referring to the clutch problem that affected Montoya on Thursday, McLaren CEO, Martin Whitmarsh, said; "It is important to say that it is not unusual for problems to occur during this stage of the testing process and it is better that these issues are resolved now and do not happen over a grand prix weekend."

"We put 1,100 kms on one engine and 1,300 kms on another, when Pedro (de la Rosa), Juan Pablo and Kimi posted competitive lap times." revealed Norbert Haug. "The final test in Barcelona before the first Grand Prix in Melbourne will give us an even clearer indication of where we are compared to our competition."

Michael Schumacher was third quickest, though he was almost a second off Button's time. The German was joined by Luca Badoer, both drivers at the wheels of F2004 Ms. The day's programme focussed on set-ups, engine, new components and Bridgestone tyre development.

It was another good day for Red Bull's David Coulthard, the Scottish driver finishing fourth quickest. The former McLaren driver was joined by Vitantonio Liuzzi, one of several drivers to experience an 'off' during the course of the day.

Mark Webber and Nick Heidfeld were on duty for WilliamsF1. The German spent much of the day working on tyre evaluations, while the Australian, in addition to working on set-ups, completed a race simulation. Between them, the WilliamsF1 drivers completed 243 laps.

"Throughout the week, the drivers concentrated on set-up evaluations as well as tyre testing," said test team manager, Tim Newton. "The car has proved particularly reliable over the four days, allowing both drivers to clock up an impressive total of 3,259kms. This has provided us with invaluable data to work with in the weeks leading up to Melbourne."

Although the Toyotas continue to show good reliability, both Ricardo Zonta and Ralf Schumacher were over 2s off Button's pace, and 1.5s off Montoya's. The German and the Brazilian concentrated on long runs, with Zonta shaking down the TF104B he will use for wet testing at the weekend.

"I must say while we seemed to struggle at times at Valencia last week," said Ralf, "here at Jerez the package we already have looks a bit better and closer to the other teams."

BAR and Toyota will carry out wet weather testing over the weekend, when the track will be artificially flooded.

Weather: Conditions were ideal, with bright sunshine and temperatures reaching 22 degrees C.

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