Rosberg: Copying diffusers to take time

Rosberg's Williams team, along with Brawn GP and Toyota, got a boost on Wednesday when the FIA ruled the design of their double-decker diffusers was legal.

The decision means all teams are likely to try to copy the design, but Rosberg says the process will not be straightforward and reckons rivals will need time before they make things work.

"It will take many races for the others to attempt to make their cars work with that kind of diffuser and it's not a given that they'll be able to make it work," Rosberg told reporters in Shanghai.

"It's not a fact that they will automatically be quicker - it's not that straightforward. It will take a whole lot of time and even then you can't be sure it'll work."

The German driver believes Brawn GP, who has dominated the first two races of the season, is likely to continue to be the team to beat this year.

"A very strong chance, yeah... An extremely strong chance," said Rosberg. "The thing that must be said is that the development rate of this year's cars will be massive, because of the new rules.

"We put a part on and we'll be quicker from one weekend to the next, sometimes by two or three tenths. If you consider Brawn is maybe two tenths ahead of Toyota, that can disappear oh so quickly. Look a few months down the road and things might look a bit different."

Rosberg feels his team is at worst the fourth fastest right now.

"Brawn is quickest at the moment, then Toyota, and after that I think it's quite close between Red Bull and ourselves," said Rosberg. "It's looking quite good at the moment. I think we have an opportunity to qualify towards the front of the grid and score more good points."