Yamaha rider Valentino Rossi says it is difficult to understand why he continued to "suffer" in MotoGP's German Grand Prix at the Sachsenring.
Rossi arrived at the Sachsenring on the back of three successive non-scores and has recently struggled to match his three fellow Yamaha riders.
The seven-time MotoGP champion was encouraged by his pre-crash showing at Assen and showed moments strong pace during the German GP weekend.
But Rossi was a muted eighth place at the Sachsenring and finished some 19 seconds down on race winner Marc Marquez.
"Today I finished but, anyway, it was a very difficult race because I was never strong enough," Rossi said.
"For us, this weekend was important because last week in Assen, in the race, before the mistake I felt good with the bike.
"I was fast, so we had to confirm if we found a good way here in Sachsenring.
"Unfortunately, during practice sometimes I had quite a good pace, but anyway I was not fast enough. So we suffer, we continue to suffer - and we need to understand why."
Rossi said choosing the medium rear Michelin tyre - as opposed to the hard compound that team-mate Maverick Vinales used to finish in second place - did not work out.
But Rossi says it was not the overriding factor for his muted performance.
"We start with the medium [tyre] that we knew was a little bit slower, but we expected [it to be] more constant, especially because from the Michelin side [and] from our calculation, it looks like the hard does not arrive [and perform] at the end.
"So we tried the medium but unfortunately the medium didn't have grip from the beginning and, anyway, at the end I was in a lot of trouble.
"But apart from the tyre, I think that we have some other problems because I am not able to be strong, to ride the bike well as I did last year."
Rossi says he and his Yamaha team must figure out his recent run of form, as last year's run of fives races between Le Mans and Sachsenring was his best spell of form in 2018.
The Yamaha rider entered the weekend following comments from MotoGP legend Giacomo Agostini about whether he could match leading riders.
"Last year these five races [Le Mans to Sachsenring] was the better part of my season, I was always very competitive and I did some podiums, but always good races," said Rossi.
"But this year, especially in the last four races, we suffered very, very much.
"So we need to analyse the data, we need to understand why because I don't feel good with the bike and I am a lot slower than last year because today I am 20 seconds slower than my race of 2018.
"This is very difficult to understand, we need to find a way [and a solution]. "