Team Rahal will focus on Indy Racing

Rahal is the latest in a long line of teams to leave Champ Cars.

Team owner Bobby Rahal said: "No-one agonised more about this than I did. I felt that it was in the best interest of Team Rahal.

"I truly believe for open-wheel racing to regain the popularity that it had, there really needs to be one series, the focus on one series."

Rahal, a three times champion, entered one-car teams in both US open-wheel championships last year.

But he will now run two cars only in the IRL from the Motegi event in Japan on 18 April.

Mexican Michel Jourdain Jr, who drove for Rahal's Champ Car team last year, will remain in the series, which has two events scheduled in Mexico this year.

Rahal follows team owner Adrian Fernandez's recent move from Champ Car to IRL, which has America's most prestigious race, the Indianapolis 500, as a central attraction.

The IRL season opened with 19 cars at Homestead, Florida earlier this month, but the recent defections could increase the field to 22 at Motegi.