May 6 (GMM) Rubens Barrichello said he made the decision to leave Ferrari halfway through a grand prix in 2005.

The Brazilian veteran, who will set a new record as the longest-serving grand prix driver in formula one history this weekend in Turkey, reveals that the final straw was a radio call during the infamous US grand prix at Indianapolis.

Despite the fact that only six Bridgestone-shod cars were contesting the race, Barrichello recalled to the Brazilian television network TV Globo that he was asked to let his teammate Michael Schumacher pass him -- despite the German not being in the hunt for the title that year.

"The team invited me to slow my pace so that Michael could get closer to me and to pass me," Barrichello, who is now 35 and a Honda driver, said.

"In this moment I knew that the time had come for me to go. That race in the United States was crucial," he added.

Ferrari team members insisted throughout his tenure between 2000 and 2005 that he was joint number one, but Barrichello now concedes that he was in fact Schumacher's subordinate.

"When I signed the contract," he explained, "there was nothing to indicate that the drivers would be treated differently."

History, however, records several instances of team orders, most famously when the Ferrari drivers were booed at Austria in 2002 after Schumacher inherited Barrichello's lead at the chequered flag.

Barrichello said: "Inside, I was often angry about it, because everyone claimed that there were no differences between us, but it was an unequal battle."