Mercedes F1's Wolff expects "bumpy road" with Hamilton and Rosberg

On Thursday evening Rosberg signed a two-year contract extension to take him through to the end of the 2018 F1 season, the same as team-mate Lewis Hamilton.

Following the difficulties and on-track clashes between the pair during their three-and-a-half years together, Wolff recognises in continuing to have two 'number one' drivers, there may be more problems ahead.

"I'm never confident we're on top of the issues [with them]," he said.

"It's rock and roll, or if they rock the boat, but we are conscious of that decision.

"We know that sometimes it can be more of a bumpy road having two number one drivers in the car that keep pushing each other, but that raises the performance of the car.

"It gives those moments where it's about managing a difficult situation, so we are conscious about that."

Wolff has naturally ruled out ever making either Hamilton or Rosberg the lead driver.

"It's always very clear with the two of them this is the philosophy we follow of having absolutely equal material and equal opportunity," added Wolff.

"I don't see this happening. I hope it goes until the end. It's exciting for us and exciting for the fans.

"It might make me grow some grey hair, but up until now I'm doing OK."

Rosberg's new deal ends recent speculation on his future, although Wolff conceded the deal was never "done until it's done and signed".

Wolff added: "We did that yesterday night after a couple of months of discussions.

"It was never in doubt we wanted to stay with Nico, and I guess it was of interest for him to stay in the best current car.

"We had the right spirit and right momentum in those discussions, but the final signature came yesterday night."