It's well known that Yamaha is chasing greater top speed for the 2020 MotoGP season.

"It's the main deficit we need to correct," confirmed Yamaha Racing managing director Lin Jarvis.

"We wouldn't want to put all efforts into top speed and lose in other areas, but clearly that's where we are struggling. It's probably a mix of horsepower, aerodynamics and acceleration."

The latest prototype engine was tried in post-season tests at Valencia and Jerez, but Valentino Rossi and Maverick Vinales both warned the top speed gap was still too big.

While the Yamaha engineers try to squeeze more from the engine ahead of February's Sepang tests, Vinales - the only M1 race winner since Assen 2017 - also feels he can find more performance by refining his riding style.

"I'm quite clear about what I have to improve and what the bike has to improve, at least to fight for the title," he said after the final test of 2019. "So we are working very hard for that and for sure now I have two months to improve myself."

Quizzed further, the double 2019 race winner explained: "A little bit riding style, some things to be a bit smoother, to help the bike to be faster. In that area I think I can do it, I can adapt quite good."

A MotoGP prototype is a unique machine, but Vinales feels he can work on the changes at home and won't even need a full-size motocross or dirt track bike.

"Even with the small bikes you can do it, it's the type of riding style. I will concentrate a lot to improve it."

Vinales has often topped the winter timesheets, only to strike difficulties when the racing season begins.

After being fastest in both the Valencia and Jerez outings, it was put to Vinales that he is the 'king of tests': "I'd prefer to be the king of another thing!" he quipped.

Vinales - who fought his way to third overall after a miserable start to last year's world championship - also emphasised that while his impressive testing pace may be unchanged, his approach is very different.

"Actually, we arrive with another mentality. Another programme of work. Especially in the pit box," he said. "In other tests I was doing too many laps, trying too many things and not very clear.

"Now less laps, pushing all the laps at the maximum is the important point and what we've changed."

Vinales switched crew chief from Ramon Forcada to Esteban Garcia for the 2019 season, where he took race wins at Assen and Sepang.