Casey Stoner was disappointed to qualify on the second row for the Malaysian Grand Prix, almost a second behind polesitter Valentino Rossi.
The Australian said that the handling of his Ducati changed considerably when it was fitted with soft tyres for qualifying, preventing him from making it any higher than fourth on the Sepang grid.
"I'm really disappointed because we should have been fighting for pole position," said the 2007 world champion. "I had a much better feeling with the setting at the start of the session but midway through we went to change tires and after that we suffered from a huge vibration in the bike. We still haven't worked out what it is, but we need to fix it for tomorrow."
Stoner tried to alleviate the problem by switching to his backup bike late in the session, but to no avail.
He is nevertheless confident that, after running within a tenth of a second of the pace in Friday practice, that he stands a good chance of making it back-to-back wins in Sunday's race.
"I tried the softer compound but the chattering was even worse. I swapped to my other bike but we had a different setting in it that I hadn't tried and I didn't feel comfortable," he added.
"Everything that could go wrong in the crucial second part of the session did go wrong but if we can fix this problem then we'll be in good shape for tomorrow. Certainly I'm happy with my pace in race conditions."