Mercedes' two drivers have admitted the team is struggling with tire problems in 2017.
After three races, Ferrari's Sebastian Vettel is leading the world championship, with Mercedes left to ponder the reasons.
"We have a bit to do at this test," said Lewis Hamilton, after staying around in Bahrain for the post-race test that began on Tuesday.
"We need to improve the car and our knowledge about the tires so that we are in a better position in the next race," he is quoted by the DPA news agency.
The next race in Russia should at least be cooler, which should help Mercedes. The team was more comfortable in China than at tracks with hotter conditions like Melbourne and Bahrain.
"The softer compound has been more of a struggle with the tires and also the hotter it is, more of a struggle," Valtteri Bottas admitted. "So it's definitely something for us to understand."
When is the next race?
