Sato rejoins Rahal Letterman Lanigan for 2018 IndyCar season

The 40-year-old moves across to Rahal after a single season at the Andretti Autosport squad, which yielded four top-five finishes - including the first-ever Indy 500 win for a Japanese driver - and a career-best eighth place in the standings.

But the delay in Andretti confirming it will stick with Honda engines in 2018 was understood to be the cause of Sato, who has close ties with the manufacturer, having to search for an alternative berth.

He joins Graham Rahal, who scored a pair of wins at Detroit this year en route to sixth-place in the championship, in an expanded two-car RLLR line-up, returning to the team he drove for in 2012.

"I'm excited about having Taku back with us," said team co-owner Bobby Rahal. "I have such admiration for his spirit and how he approaches everything and was so happy for him when he won the Indy 500 this year.

"The chance to bring him back to the team was too good to pass up. He and Graham get along very well and we will have two strong cars that can win any race in 2018.

"I think that will give our team a great chance at being contenders in every race but it's also going to give each of our drivers a chance to have their best years ever.

"I'm excited about it and even though the 2017 season just concluded, I can't wait for the 2018 season to start."

Sato himself added: "I am extremely happy to be back with Rahal Letterman Lanigan Racing. Bobby, Dave [Letterman] and Mike [Lanigan] have always been very supportive of me.

"The team has been ultra-competitive the past few seasons. I can't wait to be a part of it in 2018. I think we can achieve some great things together!"

Rahal Letterman Lanigan ran a single car for most of the 2017 campaign for Graham Rahal, although it fielded a second car for Oriol Servia at Indianapolis and Detroit and for rookie Zachary Claman DeMelo at the Sonoma finale last weekend.

It last ran two cars for a full season in 2013, when James Jakes partnered Rahal.