Mercedes expecting a Red Bull surge after low-key testing form

Mercedes says it is not writing off a challenge from Red Bull this season, despite its Formula 1 rival's indifferent form in testing.

Early signs from pre-season testing suggest Red Bull's reliability is better and there is more power from its Renault engine, but that has yet to be translated fully onto the track.

Meanwhile, Ferrari and Williams have had strong winters, with several drivers and teams suggesting they will be Mercedes' closest rivals in 2015.

Red Bull won three races and finished second to Mercedes in the constructors' world championship last year, and Mercedes boss Toto Wolff said his squad was expecting Red Bull to challenge Mercedes' dominant position this year.

"What we have seen in testing is that we have done a solid job. The car was quick and reliable but we have seen Ferrari making a step ahead," Wolff said.

"When you look at the GPS data, certainly on one lap the performance is spot on, but that is with the limitation of not knowing what fuel [levels] they were running.

"Then you have the usual suspects. Williams is looking good and you cannot write-off Red Bull, even though they were not really shining in testing."

Nico Rosberg said Mercedes is happy with the job its done in testing, but added the team is aware of the threat of the chasing pack.

"I am confident of the job we have done, we believe in ourselves, we are the best in Formula 1 as a team and we are the ones to beat," said the German.

"Some have been making some huge steps and we look forward to seeing where we are on Saturday [in qualifying] - but certainly we are optimistic."