Button disappointed with car handling

The championship leader emerged as fastest in the first 90 minutes but dropped down to sixth position in the afternoon as he struggled with the balance of his car.

"Qualifying and the race at the important ones. Today is not important to be quickest," Button told reporters after practice. "It's more about getting a good feeling and a good balance.

"I'm not there yet and I'm a bit disappointed with the way the car is at the moment. Hopefully we can improve overnight, I know that we will because we know which direction to go."

The Brawn driver, winner of three of the first four races of the season, reckons Red Bull and Toyota are likely to be his main rivals despite most teams having introduced big updates for the Spanish race.

"Ferrari were quite good this morning, so I don't know," said Button. "They might be playing games. A lot of people do on Fridays. We have in the past. So we wait and see. We are just running through our programme.

"If you look at the consistency of some of the cars you'd say the Toyotas and the Red Bulls are competitive, and the others I haven't really paid much attention to, but I'll look at the data tonight."

The Briton admitted he has been delighted with his start to the season, but insisted he is just focusing on the next race.

"It's obvious that I'm quite happy with how the first races went, having three wins out of four and winning a dry race," Button said. "Pretty exceptional. But as I always say you have to look at the next race, that's the way it is. You have to concentrate on the next one, and this is the next race here in Barcelona."

He added: "The first few races have been good for us. We are back in Europe now and I think we will see where everyone stands. You can't say who is going to be our main contenders yet because people are doing different things. Some people will bring a package here and some people will be improving the car race by race as McLaren has done."