Yamaha's Valentino Rossi concedes that he was "not fast enough" during Friday practice ahead of the MotoGP season finale at Valencia.
Rossi was second, albeit almost a full four tenths off teammate Jorge Lorenzo, in first practice, and then slumped down to eighth in FP2.
The Italian, winless at Valencia since 2004, said that he had had an encouraging start to Friday running but couldn't keep pace in the afternoon.
"We started this morning in quite a good way, FP1 was positive, especially in the end," he said. "I put the hard rear, it was a bit cold but I felt very comfortable with the tyre and with the bike, and in the end I finished in second place.
"We continued in the afternoon with the hard [rear] tyre, we tried also the hard front, but for some reason in the afternoon was a lot more difficult, especially the rear didn't provide enough grip, enough feeling. So after two or three laps I struggled, my rhythm was not fantastic."
Rossi pointed out that he wasn't the only one struggling with the hard rear - but admitted that he wasn't "strong enough" with the soft compound either.
He said: "I followed the practice, looks like a lot of riders have some lack of grip with the hard [rear], so in the end we put the soft [rear], and we changed also the front because I don't feel comfortable also with the hard front.
"And I improved my laptime, I improved my pace, but it's not enough, I'm not fast enough, because I'm not happy about the setting, about the balance of the bike.
"In a lot of corners I struggle too much, and I am not strong enough. Now we check the data, we try to work and we try to improve the balance for tomorrow."
Revised Michelin key for Lorenzo
While Rossi was off the pace, teammate Lorenzo excelled in the conditions, topping both FP1 and FP2.
The Spaniard, who is contesting his final grand prix weekend as a Yamaha rider, says his pace was allowed for by the tyres Michelin brought to the Circuit Ricardo Tormo.
Lorenzo said: "The tarmac here is quite grippy, also the Michelin carcass here is the same as Brno and Misano, so it's not the same as the three last races that they bring harder carcass to avoid overheating.
"So with this carcass and this tarmac, I felt very good, the warming up of the tyres is very good and the grip is good, so I felt great from the beginning this morning, from the first laps.
"I was surprised by how competitive I was today - the last five, six or seven races, I wasn't really competitive. Just arriving here and from the beginning, quick, constant and with a good feeling.
"And that's the tyre, I think. For this year, it's been difficult - but when there's grip and there's good confidence on the tyres, I am competitive."
Lorenzo admitted, however, that he wasn't sure whether he had a pace advantage over the rest of the field, pointing out Honda's Marc Marquez as a likely close rival.
"I don't know if I have the best pace because Marquez, for example, this afternoon put on the hard rear tyre and I put on the soft, so difficult to compare," he said.
"But with Marc, I think, we are the ones who have better pace, who are faster."
Additional reporting by Matteo Nugnes and German Garcia Casanova