Sauber's 'spiral' of positive events last year were key in attracting Kimi Raikkonen to join for 2019, says team boss Fred Vasseur.

The Finn surprised everyone by announcing a move back to the Swiss outfit mere minutes after it was confirmed Charles Leclerc would be replacing him at Ferrari this season.

While Raikkonen has claimed his love for driving is the reason for his decision, Vasseur believes the step forward Sauber took is what interested Kimi the most.

“We had Ferrari, Alfa Romeo and Charles joining the team, we took [aerodynamicist] Jan Monchaux, Simone Resta [as technical director] and brought them into the factory," he said to Autosport.

“Each week we had good news, it’s like a spiral. The motivation is there, the mood is huge compared to last year, the team spirit.”

The partnership with Alfa, which also brought closer ties to Ferrari, was considered the main boost, helping the team to their best season since 2015, finishing eighth in the Constructors' championship with 48 points.

“For me, drivers are the same. Good engineers you can motivate with the salary but they love racing and they want to get results,” Vasseur continued.

“We’re in a much better position to recruit, to have top guys in every single department. I have the feeling that we’re really attractive as a project.

“Drivers are the same story. Kimi knows it will be difficult for us to better than P7 without an accident [for the top three teams].

“The motivation can come from somewhere else. The fact we’re improving, we’re growing up, we’re building something – I think it’s a huge feeling for all the team members, including drivers.”

Also Read:

• Charles Leclerc: Sauber progression stopped 2018 being a 'very difficult year'
• Kimi Raikkonen's move to Sauber a 'blow for F1', says Mercedes boss
• Kimi Raikkonen surprised by similarities between Sauber & Ferrari cars

The Sauber chief is also confident the impact of the new additions to the team will be felt more in 2019, allowing them to be even more competitive in the midfield.

“We recruited a lot since last year to improve on every single part of the company and it’s paying off,” he said.

“When we started to work at the end of ’17, people joined at the beginning of ’18 and some of them were working on the ’18 car.

“Some of them switched directly to this year’s car. It’s the first results of this recruitment. I hope it will get more and more.”