Valentino Rossi went from being first in the wet, to eleventh and last of the manufacturer riders in the dry at Silverstone on Friday.
The seven time MotoGP champion led a Ducati one-two in the wet morning practice session, confirming his wet podium form from Le Mans, but improved conditions in the afternoon proved a much tougher challenge.
Losing time in several specific areas of the long Silverstone lap, Rossi was left eleventh on the timesheets and 2.334s from fastest man Casey Stoner (Honda).
The Italian was over a second behind the next fastest manufacturer rider (Hector Barbera) with only the CRT competitors, whose machines have at least a 20km/h top speed disadvantage, slower than Rossi in the dry.
“This morning went really well,” began Rossi. “We were fastest, which made us very happy since we had many problems here last year in the wet. So now we're competitive in the wet on this track as well, whereas it was a little harder for us in the dry.
“That said, I would like to have at least one more dry session because on the one hand there are a couple of things to sort on the bike, which gives us some margin, while on the other hand I'm still not riding this track well."
Rossi, who struggled at last year's Silverstone round before salvaging sixth in the wet race, added:
“There are two or three spots where my lines aren't efficient, and where I'm still losing some time. It's better than last year, but still not good enough, so I need a little time. We'll see what the weather is like tomorrow.
“Here, it's the dry conditions that are the unknown, because it always rains!”
Team-mate Nicky Hayden, runner-up to Rossi in the wet morning session, was 1.7s quicker than the Italian on his way to fourth place in the dry.
“We know our bike really likes wet conditions, and the team was obviously quite good this morning,” said the American. “With the rain shower this afternoon, we didn't really get to do a lot of dry laps, as the time went by pretty quickly.
“The track was actually pretty good as far as grip was concerned, although it was really windy out there. We learned a couple of things, but we still have more work to do.
“We need to improve the transmission ratios a bit in some spots and work to get some more stability, because the side winds made it very difficult in the high-speed parts.”