A week after announcing its intention to leave the IndyCar Series after the 2011 season, Firestone has reversed course.

Nashville, Tenn.-based Bridgestone Americas Tire Operations Inc. announced Friday morning that its Firestone brand will continue to serve as the sole tire supplier to IndyCar through the 2013 race season.

Terms of the agreement weren’t announced.

Firestone has supplied tires to IndyCar since 1996. The new agreement does not include developmental series Firestone Indy Lights. Firestone will remain as title sponsor and tire supplier of Indy Lights through 2011.

Firestone and IndyCar executives said the agreement followed a week of negotiations.

Motorsports business experts estimate that Firestone pours $7 million annually into marketing the open-wheel series.

Tokyo-based Bridgestone Corp., which owns Firestone, pulled out of Formula One racing following the 2010 season.

The Firestone announcement is good news for the IndyCar Series, which is preparing to introduce a new chassis and engine package for the 2012 season. IndyCar Series CEO Randy Bernard needs Firestone’s tires to provide a stable platform for testing of the new chassis and engine, which is scheduled to start in July.

Firestone’s connection to the Indianapolis 500 began in 1911 when Ray Harroun won the very first race on Firestone tires.

The company’s current open-wheel era began in 1991 with title sponsorship of the Indy Lights series. Firestone Racing made its return to the Indianapolis 500 in 1995, and its tires were on the winning car of the first IndyCar (then Indy Racing League) sanctioned race in 1996.

Last week, Bernard said finding a new tire supplier was a “top priority,” and that talks with Goodyear, Hoosier Tire, Cooper, Avon, Continental and Pirelli had already begun.