Jorge Lorenzo managed to improve his pace on the new Bridgestone tyres at Sepang, but the Yamaha Factory Racing rider remains bitterly unhappy with the performance of the rubber at his disposal.

Lorenzo was seventh fastest, 0.620s behind his team-mate Valentino Rossi and Repsol Honda's Dani Pedrosa at the top, but says it was 'impossible' for him to be competitive at Sepang.

"We found a better solution today to improve our situation and adapt these tyres at this track. The tyres are much harder in the sidewalls," said Lorenzo, whose riding style relies significantly on plenty of edge grip from the tyres.

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"At this track, with this tarmac that is very slippery, it's not the same as Phillip Island or Mugello for example, it's impossible for us to be competitive.

"This tyre is much worse for Yamaha than it is for Honda - the difference is unbelievable. The bike is competitive, more or less at the same level as Honda, but with this tyre we are really bad. We have tried everything to improve a little bit.

"When we are in a race simulation we are working and working every lap. The problem is that when the tyre starts to drop, the problems get bigger."

Lorenzo completed 14 laps of a race simulation on the YZR-M1 but opted for an early return to his pit garage as tyre wear kicked in.

"The spinning creates a bigger temperature, so we will see at another track if we don't get any spinning. I did 14 laps and that was the longest run with soft [front] and soft [rear].

"In these conditions we had a lot of problems on the exit of corners, a lot of movement, so we decided to stop rather than take so many risks.

"In the edge there is a problem with no grip but also when you pick up the bike it spins. You can improve the feeling a little to get more grip but when the tyre starts to drop the problems get worse and worse.

"The bike is really competitive in normal conditions, like it was in the last three or four races of last year, but it's the tyres."

Asked if there were any positives Lorenzo could take away from the three-day test at Sepang, he replied: "We can finish the race with 20 litres and we made some improvements with the electronics."