Mixed weather conditions at Motegi on Friday meant it was difficult for Valentino Rossi to assess Yamaha's level of competitiveness at the Japanese track.

The factory team suffered badly at last year's wet event, but returns fresh from an expectedly strong weekend in Thailand, Rossi and team-mate Maverick Vinales finishing third and fourth, both within 1.6s of ending Yamaha's record losing streak.

One of Yamaha's top priorities for Motegi is to determine if they truly made a step forward with the M1 in Buriram, or simply benefitted from a revised rear tyre design and circuit characteristics.

Rossi was ranked ninth during the lone dry (FP1) session on Friday, when Tech 3's Johann Zarco and Vinales were close to the top in third and fifth respectively.

"It was a difficult day to have a clear idea, because today wasn't the perfect day to get an understanding of our situation," Rossi said.

"Fortunately it was dry in the morning, so we could work a bit, but my pace wasn't fantastic.

"But on the other side, Maverick and Zarco were quite strong, also concerning the pace, so this is good for Yamaha. We have to try something else, like this."

Rossi and Vinales were 14th and 15th respectively in the damp afternoon session, after staying on worn rain tyres rather than fitting soft slicks for the final stages.

"Unfortunately in the afternoon the conditions were half-and-half," said Rossi. "But I had something to try, so I stayed on the track with the wet tyres to try to understand and, from that information, we will try to make a better setting tomorrow. Especially to keep a good pace with the used tyre, which is always difficult for us.

"We hope for good weather tomorrow to understand our situation better."

Team director Massimo Meregalli added: "Vale didn't get the start we hoped for in the first session, but he and his crew managed to get things to go their way towards the end of the morning.

"We still have room for improvement. We are confident we can make more steps over the weekend to be even more competitive on Sunday and we hope the conditions will remain dry tomorrow. Every session is important, because you can always gain information.

"However, as FP2 was wet and the forecast for the race is for dry weather, we lost some crucial time to work on the set-up. We also haven't finished the tyre comparison yet, to choose a combination for the race, so tomorrow we'll work some more on that."

Meanwhile, Rossi and Vinales ended the day in special pink shirts:

"We changed our team wear for an important occasion. The pink shirts me and Maverick wore at the media debriefs are a part of Movistar's support in creating awareness for breast cancer," Rossi said.