Rossi: First test day better than entire 2017 pre-season

Rossi and Maverick Vinales spent the past season struggling with Yamaha's 2017 chassis as well as rear tyre degradation and bike performance in mixed conditions, leading the team to revert to the 2016 version as the base for this year's bike.

Both riders spent time at the top of the timesheets during the first of three test days at Sepang before ending their day early, with Rossi and Vinales ending up sixth and 13th respectively.

Rossi praised the new Yamaha, saying he was "always competitive" during the day, which was not the case in pre-season testing the year before.

"I don't remember last year one day like this," said Rossi.

"I was always competitive, I am happy because in November [at the private Sepang test] we did a good job, we understood better after the confusion during the season.

"The chassis of today is a new chassis, an evolution but is based on the 2016 [chassis].

"When I ride this chassis I feel better, my ride is more natural, I feel I perform better and when I push, I have good speed."

In addition, Rossi revealed that he was using different engines in an attempt to improve acceleration, as well as working on electronics to fix rear tyre degradation problems.

Rossi didn't do longer runs in order to conserve energy, as the first day after the winter break at Sepang is a "disaster physically".

However, Vinales said that he was focusing on longer runs, and felt that big gains have been made in terms of tyre management.

"There is a real improvement because from lap zero to lap 20 I just really do [within] 0.3-0.4s, that is very positive.

"I felt great with that, but still, I think we can improve a lot."

Additional reporting by Oriol Puigdemont