Valentino Rossi and Jorge Lorenzo got their first taste of Yamaha's new seamless gearbox during the start of the second 2015 MotoGP test, at Sepang on Monday.

The factory riders have been urging Yamaha to match Honda's seamless downshifts ever since receiving a full range of seamless upshifts for the start of last season.

Seamless technology slashes the time taken to switch drive from one gear to the next by engaging both gears simultaneously. While the shorter shifts provide a small increase in performance, riders often cite the main benefit as enhanced stability and therefore consistency.

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With Honda's main strength perceived to be braking and corner entry, Rossi and Lorenzo are hoping the new gearbox can help them take on reigning double champion Marc Marquez.

Rossi gave the new gearbox a perfect debut by setting the fastest lap time of the day, a position confirmed by a brief thunderstorm with two hours remaining.

"Everybody in our team was curious about the new gearbox and my first impression was quite positive," said the Italian. "It's not a huge difference but it's a small help in a critical point where we needed to improve.

"The bike in braking and under braking is a bit better and I think that we have to work to understand the maximum potential but the first test was good and I'm happy to finish in first position because I was fastest from this morning."

Rossi's best lap time of 2m 0.414s was 1.5s behind Marc Marquez's unofficial lap record at the first test. However track conditions were more slippery even before the afternoon rain.

Team-mate Lorenzo was fifth quickest on day one, 0.641s slower than Rossi. The Spaniard admitted it had been a tough day, albeit with the new gearbox as a clear highlight.

"Today has been very hard for me to be competitive," he began. "The setting I had from the last test didn't work so well today on a more slippery track. The positive thing is that we tried the new seamless downshifts.

"Both of us like it. It is only the first day but already it's a bit better than the old one. The bike is more stable in straight braking, so you can brake a bit later.

"Still we need to do some adjustments but it has a lot of potential. Now we need to understand how to get the maximum performance from this new technology.

"It won't completely close [the gap to Honda on corner entry] but it will be better."

Ducati also uses a version of seamless gearbox technology, with similar systems under development at Suzuki and Aprilia, returning to MotoGP this season.

The satellite Tech 3 Yamaha team are running last year's factory gearbox, meaning they also have the full range of seamless upshifts from 1st -6th (the first generation Yamaha seamless worked from 2nd-6th) but normal downshifts.

MotoGP riders no longer need to use the clutch lever when downshifting, however this is unrelated to seamless technology.