Valentino Rossi remains unclear over whether or not Yamaha have closed the top speed deficit to his Honda and Ducati rivals, which the Italian star highlights as the only weak point of last season's YZR-M1.

The 36-year-old was sixth fastest overall on the second day of the Sepang MotoGP Test, lapping in 2m 01.021s as he finished nine tenths off the fastest time set by Danilo Petrucci on the Octo Pramac Ducati GP15.

Rossi feels the 2016 M1 has slightly more power, but says he will have to wait until the first race in Qatar in March for the chance to truly evaluate the difference in top speed between the leading factory machines.

"For me [new bike has] a little bit [more power] but the speed is similar, also this will be interesting because at this moment we don't know exactly the level of our top speed compared to the Honda and Ducati and it is a great issue for us, because last year it was the only weak point of our bike," Rossi said.

"It was another hard day, a lot of work to do, but I am quite satisfied, especially because we improve a lot the setting of the bike. My pace and my best lap improved quite a lot, but we still have a lot to do.
But I think we have to wait for the first race to understand [top speed]."

With an extra two litres of fuel per race and two more engines permitted under the 2016 regulations, Rossi admitted that Yamaha could take a chance by raising the horsepower of the M1 to boost maximum speed.

"I think yes [could raise the horsepower] and I hope we can have more horsepower for the top speed, but also Honda [have same fuel/engine advantage]," he said.

"Not Ducati, so maybe we can close the gap with Ducati, but we need to understand if Honda improve, how much. We will know when we have the official top speed."

Rossi and team-mate Jorge Lorenzo are testing two 2016 Yamaha M1s at Sepang and the nine-time world champ currently prefers the bike that is closer to his 2015 machine than the more radically altered '16 model.

"At this moment I prefer the bike that is more similar to the 2015, to last year, because with the 2016 we have something good, but in braking we are having trouble," he said.

"But tomorrow I will try another time, we are not in a hurry and for me it is interesting to try in Phillip Island one time, the new bike, because you have another track. Now, bother riders are more for the bike that is more similar to 2015.

"They tried to modify the bike with tyre of last year - the Michelin of last year - so now Michelin make a step, so maybe we don't need; this is the situation."

Rossi has been unable to match the pace of world champion Lorenzo in Malaysia on the opening two days of the test and although he conceded that his team-mate is 'very fast', he also feels Lorenzo is especially strong on the harder compound Michelin.

"Jorge is very, very fast, also today I think he is faster with the harder tyre because I think [Danilo] Petrucci, [Hector] Barbera and also [Marc] Marquez make [their time] with the soft," Rossi said.

"The second fastest with the harder tyre is [Cal] Crutchlow and he is seven tenths slower than Jorge, so he rides very well and he has a good feeling with the front. We know that he is very good in the time attack, but he rides very well."

Tuesday's test was halted for more than an hour following a frightening main straight crash for Loris Baz, who came off at around 180mph after a suspected tyre failure.

Michelin withdrew the soft version of the tyre used by the Frenchman at the time of the incident and Rossi said it was clear Baz had a lucky escape.

"Like I said before, if you start to think, it is better than you stay in bed and you go back home because f**k... it is one of the most dangerous things that can happen," he said.

"Loris was very, very lucky, and we have to say thank-you, but now the important thing is that Michelin can understand why. When you ride the bike and you are on the straight, the feeling is very comfortable and you don't feel very fast but for something to happen... it is scary."