"Last week we felt we were pretty good on the race simulation. This week, not so much so far in the heat," says Button. "On low fuel I don't know, but on high fuel I would say we are lacking compared to a couple of teams out there, probably more than we expected.
"The last test I would have said the Mercedes is very strong on one-lap pace, but the Williams was quicker over a race distance. At this test the Mercedes is as quick as it was. I think the Williams is also. But now you have the Force India, which is competitive, and you also have the Red Bull that looks competitive, the Ferrari that looks a lot more competitive than last week as well, so it's changing all the time."