BARCELONA, Spain -- Lewis Hamilton has warned that McLaren's car isn't championship-caliber just yet, while world champion Sebastian Vettel led testing Wednesday for Red Bull to strengthen its status as the early season Formula One favorite.
Vettel set the fastest lap yet of preseason testing at the Catalunya Circuit with a time of 1 minute, 21.865 seconds.
Teammate Mark Webber was fastest to open the five-day session Tuesday, but Vettel cautioned against putting too much stock into the Austrian team's early results.
"It was a good day and a good time, although to be honest it's difficult to say where we are, as the lap times of the teams are all over the place," Vettel said.
Hamilton was fourth, a little more than one second behind Vettel, after his session was cut short by an exhaust problem.
"Do I believe I have a car to win the world championship at the moment? I don't, no," Hamilton, the 2008 champion said. "But that doesn't mean it won't become a world championship-winning car."
Hamilton isn't panicking, as McLaren has been known to be one of the best teams at developing a car through a season.
"This is testing. This is what it's all about, finding where your weaknesses are so you can build on them and fix them," he said. "It was a bit on and off today, it wasn't a great day for us. But in terms of how the car felt, there was an improvement with some of the upgrades we have. So that is at least a positive, it's not all negative."
Toro Rosso driver Sebastien Buemi was nearly a half-second behind Vettel, ahead of Renault's Vitaly Petrov, while Ferrari driver Felipe Massa was fifth in 1:23.324 as the Italian team tested a new exhaust system.
Testing continues through Saturday, with the season opening March 27 at the Australian Grand Prix.