Rosberg encouraged by new Williams

The German was pace-setters Ferrari's closest challenger in Valencia yesterday and further strong long run pace today has pointed towards a step up in form for Williams this year.

But despite being happy with his early impressions of the car, Rosberg is determined to keep his excitement in check while testing continues.

"The first feeling was positive for me when I drove the car," he told autosport.com about his early impressions. "It felt straight away like a nice step and that is always good to feel when you are straight out of the garage. It is a nice step forward.

"But I don't want to say, 'wow, it's unbelievable.' because there is no point to say that. It's early days and we have to wait."

Rosberg admitted that the long run pace had been particularly encouraging, especially because the car was still quite a handful to drive at the limit.

"The car is not always easy to drive," he said. "At the moment, it is not so easy and we have some issues that we need to solve that were there on the first day.

"But I'm happy. The long runs seemed good and at least it was promising."