Aprilia has settled on the Step 1 specification of its RS-GP machine to start the 2015 MotoGP season but, with one test remaining, is still seeking a solution to Marco Melandri's woes.

Making its Factory MotoGP return one year earlier than initially planned, Aprilia will use an upgraded version of its ART Open class machine this season. An all-new bike will then debut for 2016.

Aprilia brought two different 2015 RS-GPs for the opening test at Sepang, a Step 1 bike that made its debut during testing in November plus a new Step 2 design. Melandri and team-mate Alvaro Bautista both preferred the Step 1, struggling for feeling and grip due to different weight transfer characteristics on the Step 2.

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Work on the Step 2 continued with test rider Michael Laverty during the first Michelin tyre test, and some 'radical' set-up changes brought an improvement. But by the conclusion of the second Sepang outing the decision was taken to race the Step 1.

"We brought the Step 1 bike here [to Sepang 2] and also some components of the Step 2, which we tested on the Step 1. Anyway the layout, the basic configuration of the Step 1, is still the best," Aprilia Racing manager Romano Albesiano told Crash.net.

"The overall balance of the Step 1 bike is very good. Okay, we couldn't improve with the Step 2 but we are quite satisfied anyway because the Step 1 bike is working well. We believe it's a good base for starting the season.

"Now we will make some improvements from what we learned here, but details. For example the Step 1 fuel tank is not big enough to finish the race so we have to put some more fuel somewhere. It was a real laboratory bike! We will find some extra room for the fuel, prepare all the parts and go racing."

The Italian added: "It looks like we are very good on handling. We are losing something on the straights and exiting the corners because, okay for sure we have less power compared to the best competitors, but also we have to tune our traction control. The time we are losing on the exit is much more than the power gap alone would explain."

Indeed, Albesiano is satisfied with the output of Aprilia's new, pneumatic-valve, powerplant and initial engine updates will focus on reliability rather than performance. The seamless gearbox "we are testing at home. It's promising but not ready yet."

Bautista improved from 21st and 3.057s behind the best lap time at the first Malaysian test to 19th and 2.195s from Honda's Marc Marquez at the second test.

"Alvaro is really happy with the front especially," Albesiano said. "Looking at him on the racetrack is fantastic. He looks very comfortable. We still have many things to improve. Some engine brake but the traction - as I mentioned before - the drive out of the corner is where we lose most."

Meanwhile Melandri, returning to MotoGP after four years in the World Superbike championship, was left at the very bottom of the timesheets.

"Marco still has not reached a good confidence with the bike," Albesiano said. "We have tried many, many things! We brought the Superbike [RSV4] because we wanted him to ride something he knew very well and kind of restart. He had some positive feeing but it is not the way. So we are still struggling!"

Aprilia's MotoGP machine is based on its World, Superbike title-winning RSV4. If Melandri still wasn't comfortable on the RSV4, a bike he took to six victories in WSBK last season, does that mean it is the Bridgestone tyres that are the main issue for him?

"Probably it's a big part," Albesiano replied.

Just three more days of testing, at Qatar this weekend, remain before the start of the racing season.

"Maybe a different track could be better for Marco," Albesiano added. "At the moment he hasn't the right feeling leaning the bike. The bike has some movement. So we are trying to stabilise the bike in that situation."

Going into the corners?

"Yes. That is the main point. The turning of the bike is also not what he is looking for. We'll keep trying."

Melandri, a former MotoGP title runner-up, will start his first grand prix since 2010 at Qatar's Losail circuit on March 29. It will also be Aprilia's first race as a factory entry since 2004.

"I would be very satisfied if we could finish the race between 10th and 15th position. That would be for me perfect," Albesiano declared.