Formula One begins its European leg with Sunday's 66—lap race. Button said he felt “pretty well prepared” with McLaren bringing upgrades to a car that gave the Briton his second victory this season in China.

Button leads the championship with 60 points with Nico Rosberg of Mercedes, Alonso and McLaren teammate Lewis Hamilton all within 11 points.

Vettel, who has 45 points, also arrives at the Circuit de Catalunya a favorite since Red Bull has started from pole in each of the season's first four races although reliability problems have left Vettel with only one victory from three starts at the front of the grid. Qualifying is key in this race, with the last nine winners having come from pole.

“Statistics are nice for you guys but for us it's more the (race) day that counts and the moment,” Vettel said on Thursday. “Pole is always important (because) where you put the car on Saturday will determine your race result quite a bit on Sunday.

“(But) the target is the same — start from pole and try to win the race.” Like Red Bull, Ferrari has had some technical problems although Alonso believes the Italians can deliver at a track where the Spaniard won four years ago. Alonso will try out a new rear wing in Friday's practice before deciding whether to use the aerodynamic upgrade that has so far given McLaren a slight edge.

“Hopefully we can have no problems with the engine,” said Alonso, who doesn't expect the pecking order to change much from the upgrades. “We need to maximize our potential in the coming races. We have a very strong car but maybe we didn't take all the points we should have.” Teammate Felipe Massa is also looking to rebound from two sub—par performances as the Brazilian driver has 41 points, one better than the season's biggest surprise — Robert Kubica of Renault.

“I was hoping to have a bigger upgrade here,” said Kubica, who warned that the French team's strong start could be reined in if other teams bring better improvements. “If they do, we might be in a bit more trouble.” Michael Schumacher is counting on Mercedes' upgrades to help the seven—time champion get back in the title hunt.

Schumacher has only 10 points, mostly due to his season—high sixth—place finish at the opener in Bahrain.

If Schumacher doesn't get an improved car, a shake—up could instead be provided by the race conditions.

Thursday's cold weather served as a prelude to the rain that is expected over the coming days.

“Rain conditions always change the chances, make it more open,” Force India driver Adrian Sutil said. “It depends when the rain starts on the weekend. If no one has a chance to practice (in the rain) then you can see a crazy race with a lot of surprises.” With Alonso expecting considerable home support, Vettel believed every little detail would make the difference.

“I had a haircut and I see Fernando did too,” the young German driver said. “Hopefully I dropped more (hair) than he did so we can take a bigger step forward.”