Stoner: Rossi will improve in qualifying

The championship leader topped both practice sessions at Assen today, while Rossi was fourth quickest and 0.3 seconds off the pace in the faster afternoon session.

But Stoner is certain that Rossi will find more speed tomorrow.

"Valentino has always done this in the past, especially in the past couple of years," he said.

"I think on the first day, he's building, building and then becoming faster.

"Hopefully we can stay one step ahead. We'll see if Valentino improves again tomorrow, and I'm sure he will."

Rossi was reasonably satisfied with his practice performance, but hoped that the weather remained dry for Friday so he could make more improvements.

"This morning was actually better than this afternoon, even though we were faster in the second session," he said.

"Our initial base set-up this morning felt quite good but this afternoon we tested some different things and honestly I didn't have such a good feeling.

"Our tyre choice seems to be okay and we have some softer tyres here which should work better in lower temperatures, as we should be able to get the heat into them faster.

"We've started out okay today but we need to improve some things so I really hope it's not going to rain tomorrow."

He said he was not surprised by Stoner's dominance, and that he would focus on his own performance.

"Now is no more a great surprise - he is fast and I think he will be fast for the future, for the rest of the season and maybe for the rest of his career," said the Italian.

"More than him, we have to look at us."

Stoner added that he would not be tempted to focus only on championship rival Rossi, as other riders could also challenge for pole position and the race win - particularly Kawasaki's Randy de Puniet, who was second in practice.

"At the moment Randy de Puniet is also riding very well," said Stoner. His lap times were very impressive.

"We need to concentrate on whichever other riders are nearby."

The Australian said he was focusing on race set-up rather than single lap pace when he set his quick times in practice.

"It's our goal to find the best race set-up possible - not to do the best lap time or the best qualifying lap, just to get the best race set-up," Stoner insisted.

"And we've been doing that at every race this year. We've won five races, and obviously the system is working, so we just tried to continue with this system."