There is no easy explanation for Yamaha’s sudden improvement in performance, with Rossi challenging for pole before qualifying second, and Vinales a close fourth.

“It is a surprise also for us, because in the test here we were in trouble,” said Rossi.

One change since then has been a different rear tyre from then, with a harder construction as used in Austria, and a different combination of compounds. This is a new tyre for particular conditions, according to Michelin, commissioned after tyre endurance problems in severe heat at the tests.

For Rossi, the apparent breakthrough was a combination of the tyre and the track, which offered adhesion that has been in short supply for the M1 all year.

The bike was “very similar” to that on which Rossi had qualified 18th at Aragon, but “maybe it is a better marriage between the tyre, the track and the M1.

“I have felt good from the beginning of the weekend. It seems we can make the tyre work in the right way, and that makes it easier to make decisions,” he said. Thus they had made productive setting improvements over two days of practice.

But being unable to understand the reasons was a worry. “I hope we can be strong at other tracks, but I reality I think it is just this track and the tyre,” he said. “We will talk again on Sunday, after the race.”

Vinales was no closer to an answer, but did credit some balance changes “that we should have made months ago” for giving him a bike on which he could feel comfortable and “ride as I like”.

Rossi had rejected the new twin-wing aero fairing he tried yesterday, since it offered very little advantage. Vinales had yet to fit the elaborate second-guess fairing.

Rossi, Thailand MotoGP 2018

By Michael Scott

Photos GnG