Valentino Rossi has praised Yamaha's new seamless shift gearbox, but is still unsure when it will make its MotoGP race debut.

Ducati and especially Honda already use their own versions of the special gearboxes, which slash the time taken to change gear.

This improves acceleration, but the main benefit is in terms of stability, with the motorcycle less 'upset' during gear changes.

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Reigning double champion Jorge Lorenzo and factory team-mate Rossi made their debut on Yamaha's version of the technology in a private test at Brno, during the MotoGP summer break.

Speaking at Indianapolis on Thursday, the Italian hailed the handling improvement from the gearbox: "[The new gearbox] doesn't change a lot in terms of lap time. We tried to make some comparison. A lot of people speak about two-tenths a lap - I think it is less than two-tenths.

"But the big improvement is, I think, in 20 or 30 laps because the bike becomes a lot easier to ride, more stable, more stable in acceleration, but also more stable in braking.

"For me, it's better for the tyres, less stress for the tyres, and also it's very good for the riders because the bike becomes more easy to bring at the limit and more difficult to make a mistake. So I think it's something very important for the race distance, more than for one lap.

"The feeling is fantastic. It's a great emotion to ride with the gearbox, and acceleration is very good.

"If you need to change gear [when leaning] on the very edge you can do it. You don't have to modify the riding style, but you can use some [new] tricks to get the maximum from the gearbox to go faster.

"When can we [race it]? Sincerely, I don't know. Me and Jorge push a lot for to have as soon as possible because is very good. And now it's a little bit bad feeling to come back to the normal one, because the normal one feels very fast before you try the seamless.

"But the Japanese say that we have to be quiet, the gearbox is a critical point [for reliability]. We have to be ready 100 percent, but I hope [to race it] as soon as possible."

Lorenzo, 26 points from MotoGP title leader Marc Marquez, is also pushing for the earliest possible race debut. "For the moment it's not ready. I hope to use it as soon as possible for to win this world title," said the Spaniard.

With both Lorenzo and Rossi having already opened the fourth of their five engines for 2013, it may not be technically possible to introduce the new gearbox until the closing rounds - unless it is compatible with the engines already in use.

"I don't know if it possible to put the gearbox already on this engine or we have to wait for the last engine," said Rossi. "Seriously, I don't know. If we have to wait for the last engine for sure, we speak about the last two or three races, not before."

Lorenzo is third in the world championship, behind Honda riders Marquez and Dani Pedrosa, heading into this weekend's Indianapolis round.

Rossi, riding in his comeback Yamaha season, is fourth in the standings but already 46 points from Marquez. With an eighth MotoGP title unlikely this year, The Doctor may feel more comfortable taking a gamble on the gearbox in pursuit of more race wins.