Valentino Rossi had a race to forget at Aragon on Sunday, finishing in a distant eighth place after grip problems for much of the 23 laps.

The Italian joined his fellow Yamaha riders in selecting the hard-rear tyre, a decision they would later question.

"I knew my pace was maybe not enough to fight for the podium, but I hoped and expected to be stronger," admitted Rossi, who had qualified in sixth.

While the likes of team-mate Maverick Vinales and Petronas Yamaha's Fabio Quartararo faced grip issues late in the race, Rossi was in trouble after just half-a-dozen laps and finished 18-seconds behind Vinales.

"The race was very difficult because we started with the hard-rear tyre like the other Yamahas," he said.

"Quartararo and Maverick had some problems at the end of the race but I had a big, big drop from the rear tyre already after 5-6 laps. So unfortunately I had to slow down and my pace was quite bad."

While the soft rear tyre - as used by the podium trio of Marc Marquez, Andrea Dovizioso and Jack Miller - might have helped, the fact Rossi hit grip issues so much earlier than the other remaining M1s (Franco Morbidelli was taken out on lap one) proved he still has a set-up issue to solve.

"It's not a problem of the tyre, but is more a problem of us, our setting, because in the second half of the season we modify the bike and I was more competitive in general, but we always have this problem of rear grip and suffer more than Quartararo and Vinales," he said.

"We need to continue to work and try to understand the way to improve and to be more competitive."

Unlike Vinales, Rossi was again racing with the new carbon fibre swingarm and exhaust. Might that have been a factor in the grip woes?

"I had this lack of grip already from Austria for example or from Silverstone when I had the old stuff. So for me, no," Rossi replied. "It's something else, because I have a lack of rear grip especially on the edge. I slide very much, and when you slide on the edge you damage more the tyre. So you go more slow and damage more the tyre. We need to find a solution to improve."

Rossi remains sixth in the world championship but is now ten points behind Vinales, who finished as the leading Yamaha in fourth place.

The Spaniard looked defenceless against the Ducatis of Andrea Dovizioso and Jack Miller on the long straight and Rossi confirmed top speed remains a Yamaha priority for 2020.

"It's very important because it's a lot easier if you're fast in the straight. You have time for free and if you have to fight it a lot easier to overtake," he said.

"We know it's our tough part, the top speed, and we push a lot with Yamaha to improve next year. It's not easy because the gap is quite a lot but I think Yamaha know they have to work under this point of view."