The Honda-powered team, with Briton Jenson Button and Japanese driver Takuma Sato, tried out the French tyres for the first time in Barcelona on Tuesday after the post-season test ban ended.
BAR said in a statement they were running an interim 'concept' car alongside the old BAR005 to evaluate new technologies before launching their 2004 challenger in February.
"This week's programme is essentially the start of our 2004 season," said technical director Geoff Willis.
"We have made significant advances for next year with both engine and transmission, and we are eager to start evaluating those with the benefit of our 2004 Concept car."
Willis said the change of tyres meant the team faced a steep learning curve. He said BAR, fifth overall this year, planned to carry out 'substantially more' testing in the next few months than they had done in the run-up to the 2003 season.
