Driver rivalry pushing Toro Rosso forward in F1 - Carlos Sainz Jr

The Italian-based team finished seventh in the constructors' championship, 11 points adrift of Lotus, after a season that was compromised by unreliability and an underpowered Renault engine.

Verstappen finished 12th in the drivers' championship with 49 points, 31 clear of fellow rookie Sainz, who suffered three more retirements than his team-mate.

"I knew Max was ready for F1," Sainz told Autosport. "I said [during 2015 pre-season] that we are both in the same boat, fighting hard.

"I've never had a team-mate where our data looks so similar to each other, we match every speed in every corner, everything is so similar.

"We learn from each other, we keep pushing each other and this is making the team go forward and maybe being ahead of where we should be."

Sainz believes only small adjustments are required to make 2016 a more consistent year, and he expects Toro Rosso's switch to year-old spec Ferrari engines to fix some of the problems from last season.

"The winter is very important, it's where you analyse everything you have done," he said.

"You put the data back into your computers and you come back stronger.

"In the past, I've always made quite big steps one year to the other so I will try and do another big step and learn as much as I can.

"You don't always have time to reflect on what you have done so the winter is important.

"The experience I have and the analysis I do will make 2016 a better year without changing much.

"With a bit less reliability issues and a bit more power maybe we can be in top eight and top six, rather than top 10."