Toyota worried about tyre degradation

"It's very difficult. Basically neither of the tyres are right because the soft is too soft and the hard is too hard, so you are never in the right window," the Italian Toyota driver said after Friday's practice.

"It takes a while before you can get the hard tyres working and the soft ones are straight in but after three laps just wear off.

"It's amazing the degradation. It's difficult to work with these tyres. You change from one to another and you don't know what's going to happen and it changes completely the balance. It's so difficult to work in these conditions."

He added: "We are talking about two tyres neither of which are working properly because the soft are too soft and the hard are too hard. It's hard to work with them. It's going to be a hard weekend to manage the tyres."

Trulli set the third fastest time of the day, but admitted his car was very hard to drive.

Team-mate Timo Glock also said that he struggled with the balance of his car and put part of the problem down to the difficulty of generating heat into the harder tyre, and the degradation of the softer option tyre.

"The primes are tricky - the front tyres struggle quite a lot," he said. "On options it is much easier, but over the long run they are difficult.

"On the prime tyres it looks better on a long run, but the warm-up is tricky."

Glock is expecting Saturday's qualifying session to be closely fought, and is hoping that the balance problems that hit in free practice will have been eliminated.

"It looks really close," said Glock. "One second covers the top ten so it will be difficult in qualifying. Hopefully we will get this problem sorted out."