Barrichello believes McLaren are struggling

"Renault are the team who have made the biggest impression," said Barrichello, following testing of the new Ferrari F2004 at Mugello in Italy this week.

"The car is fast on the single lap and very consistent in race simulations."

Barrichello added that the new Ferrari, which he drove for the first time on Saturday, was better than the previous car "in every area".

The Brazilian proved the car's potential by setting a lap record at Mugello on Monday.

"My first impressions of the car are all positive," he said."

However, he was less complimentary about Ferrari's fierce rivals McLaren, who were hampered by mechanical problems in testing last week.

"McLaren have not set thrilling times in Valencia, while in Barcelona they had technical problems," he said.

"Obviously we do not know if they lapped with a large quantity of fuel in order to hid their true potential.

"We know that the Williams FW26 is very fast on a single lap, but less so on long distance runs," he added.

Barrichello will team up with world champion Michael Schumacher for the fifth year running when the season begins on 7 March in Australia.