Formula 1 championship leader Sebastian Vettel admits his Red Bull team needs to make changes ahead of Saturday's qualifying for the season-ending Brazilian Grand Prix.
Vettel posted the second-fastest time in the two practice sessions Friday amid scorching heat at the Interlagos, behind McLaren's Lewis Hamilton. Vettel's Red Bull teammate Mark Webber was third-fastest in the morning and afternoon.
"It was very hot today and the track was slippery which made things difficult," the German said, adding his team had been misguided by predictions of rain.
"The conditions were the same for everybody. We have to learn our lesson and improve the car. There is still a long way to go."
Hamilton, who is racing for McLaren for the last time before joining Mercedes next season, was satisfied with his opening-day performance.
"I hope that we can maintain this form or maybe go even faster tomorrow," the Briton said. "We are trying our best to achieve our targets but this track is so hard on the tyres that it's difficult to make predictions."
Thunderstorms and rain have been forecast in the Sao Paulo metropolitan area Saturday with wet conditions expected to continue for Sunday's main event.
Vettel, who has a 13-point lead over Ferrari's Fernando Alonso at the top of the drivers' standings, needs only to finish fourth Sunday to secure his third consecutive championship.