Rosberg fears cooler Bahrain GP conditions could hurt Mercedes

Track temperatures fell to an unusually low 24 degrees track and 20 degrees air during the evening session, and are forecast to only be a little higher for qualifying and the race.

Mercedes' slick tyre selection for the Bahrain event has leaned towards the softer options, with six soft sets and six super-softs for Rosberg and team-mate Lewis Hamilton, plus just one set of mediums.

Main rival Ferrari opted for three mediums, four softs and six super-softs for Sebastian Vettel and Kimi Raikkonen.

"Temperatures are very surprising, it's really cold out there," Rosberg admitted after topping both Friday sessions.

"We had to already choose the tyres for all the races a few months ago in the winter, so we're stuck with them.

"We can't now say 'it's colder, let's change them'.

"That could be challenging for us this weekend because the colder temperatures destroy the tyres much more.

"We don't regret it , but it's going to be more difficult."

Although Ferrari was in the lower part of the top six on Friday and over a second off Mercedes' pace, Rosberg thinks the strategy options could make it a close race.

"There could be a few surprises in the race, because with the tyres there are so many different strategies you could do and if there's a safety car or something there could be massive surprises," he said.

BAHRAIN 'NOT PARTICULARLY STRONG' FOR HAMILTON

Though Hamilton has won in Bahrain for the past two years, he admitted after being outpaced by Rosberg on Friday that he feels his team-mate is quicker around Sakhir.

"Nico is always very fast here, it's always a huge challenge to beat him on this track," said Hamilton.

"Bahrain is always a difficult place to get the right set-up, it's not been a particularly strong circuit for me.

"We have to work incredibly hard to try and get the maximum out of the car.

"I haven't got the balance right yet. If I get it right, we shall see."

The reigning champion believes he is in better shape on long-run pace.

"I just have to keep dialling in the car. I need to find some time in the last sector," said Hamilton.

"There is some work to do. It's not impossible, but it's going to be hard."