'We don’t want to race with the 2016 chassis' - Valentino Rossi.
Yamaha took over from Honda at the top of the timesheets on day two of official 2018 testing at Sepang in Malaysia.
Movistar riders Maverick Vinales and Valentino Rossi were separated by just 0.035s at the front, on a day when 0.392s covered the fastest nine riders.
"Today was a positive day because I have always a good feeling with the bike and I was quite competitive also in the pace," said Rossi, who beat his best Sunday time by almost one-second.
"We improved a lot the performance with the used tyre compared to last year, that is very important, but you know the fight is very tight. Everybody is there. Also with the pace, very close.
"So we need to concentrate very much on the small details for try to arrive in front. It's just the beginning but to start in a good way is very important. Last year we start in a bad way and during all the season, with ups and downs, we struggle. Usually when you start well it's better."
Rossi's strong start - in stark contrast to last year's forgettable pre-season - appears largely been down to a switch back to the 2016 chassis concept. The nine-time world champion explained they are trying to use the best parts of that frame as a base, while working on small modifications.
"The chassis is very similar to the [standard] 2016. The heart, the idea, is like the 2016 but we try to modify something around. And also today I try something with one chassis that was slightly different. Maybe tomorrow I have another one," said Rossi, who also rode his firs lap with the new Yamaha fairing on Monday (see separate story).
"We work because we don’t want to race with the [standard] 2016, because it is the old chassis.
"In the test here in November we tried to understand what it is that I like about the 2016 chassis. What worked well. And I think that we have the idea more clear now, also Yamaha, and we try to work around the base of 2016."
In terms of his physical condition after last year's broken leg, Rossi revealed:
"I can train in a good way. I also had ten days more than last year because last year I had to go around for Yamaha and this year I arrive in a better condition. I'm very happy because today I'm better than yesterday. Yesterday was difficult.
"But I'm still not 100%, especially with the breathing, because with the leg I cannot run still. So I need to work for March, but I am already at a good level. I think this test is difficult for everybody. Also the young riders."
Testing at Sepang concludes on Tuesday evening.