Romain Grosjean was encouraged by his performance in Hungarian GP practice on Friday

Red Bull stamped their authority on the Hungarian Grand Prix during opening practice but nearest pursuer Romain Grosjean is optimistic Sebastian Vettel and Mark Webber won't have it all their own way come the race.

Temperatures climbed past 30 degrees Celsius on Friday and they are forecast to soar higher still on race day. Lotus, of course, like the heat and once again it appears to represent their best chance of success. Such a scenario played out during the German GP three weeks ago, when Grosjean briefly appeared capable of challenging for victory before being forced to settle for third place behind Vettel and team-mate Kimi Raikkonen. "It may change the tyre life of the option and medium - they quite like the heat and the temperature. So it might make them work even better," Grosjean said. "The medium might be different so we need to keep an open mind and a good communication with the team for the strategy in the race." So can he, or anyone, stop Red Bull? "They are quick, but they are very often very quick. I'm not really surprised, to be honest, by their speed. We need to see them on Sunday." Raikkonen, meanwhile, had a more problematic day, struggling with both understeer and, during the morning, a water leak caused by his car's drinking system. The Finn ended P2 eighth fastest overall but could not get a clear lap on the narrow, twisting 4.381km track. "We had some issues at the beginning of the session and lost a little bit of time. Then I couldn't get a lap time on the soft tyres because of traffic," Raikkonen said. "It was a bit difficult today, just too much understeer. I had to work on one or two other things but this is pretty normal. It was a bit more tricky because of the new tyres, which are not exactly the same as we're used to, but I'm sure we'll be okay."