Yamaha has already confirmed that it will be moving its Factory-Spec chassis 'in the direction' of the older A-Spec machine for the 2021 MotoGP season.

But Wilco Zeelenberg, team manager of the Petronas Yamaha squad that took the A-spec to such great success with Franco Morbidelli last season, has now explained that 'turnability' is the feature the Factory-Spec is seeking to regain.

"It was not a '19 bike, but it uses the '19 chassis," Zeelenberg said of the A-Spec bike. "The '19 chassis is different to the '20 chassis, the size is a little bit different in width, but not in length or whatever.

"So we cannot change that, but the [Factory-Spec] riders were actually quite happy with the handling [in testing] but it was clearly decided on tracks where we did not have the problems.

"In Jerez we did not have a problem, in Sepang we did not have problems. But at other tracks during the season, you arrive in situations where you have different problems than you expected.

"So that's the area where they want to improve the '20 chassis, to have the same turnability as the '19."

While the A-Spec bike used the proven 2019 chassis, a redesigned airbox to boost top speed required modifications for the new Factory-Spec chassis.

"Clearly, they made the 2020 [Factory-Spec] bike to be faster on the straight. So they made some changes to do that," Zeelenberg said.

"They made a big jump last year to decide to go to the 2020 bike and they did not do that for many years. They were always making small steps, but last year they made quite a big step and it was clear the bike had some problems in some areas."

Although the changes made performed well during pre-season testing, once racing began the Factory-Spec trio suffered from inconsistent form.

That included an end-of-season slump that saw Petronas Yamaha's former title leader Fabio Quartararo, plus Monster Yamaha's Maverick Vinales and Valentino Rossi fail to finish on the podium in the final six races.

Meanwhile, Morbidelli and the A-Spec went on to win three races and finished second in the world championship behind Suzuki's Joan Mir. The four Yamaha riders will remain on the same spec for 2021, when Quartararo swaps seats with Rossi.

"For us it was quite clear that the combination of the '19 bike, chassis, and the riding of Franky was better for sure at some tracks," Zeelenberg said. "But I don’t want to break down the performance of Franky because also to do what he did has been very special. It was not just 'he has the best bike it's easy to win'. It isn’t.

"How he won in Misano, to lead and control Vale in the beginning and escape was a great performance and it takes a lot out of the rider to do these kind of things. I don’t want to say anything [to play down Morbidelli's results] but for sure he had some benefit in some areas because the other three Yamahas were struggling in those areas."

While Yamaha is confident they have diagnosed the chassis problem after comparing data between Morbidelli's bike and the Factory-Spec machines, there will now be only six days of official pre-season testing in which to pick the right parts before the opening race.

"We will have four riders here in Qatar and if they bring a couple of chassis to test, or swingarms or whatever, then they need to have all the parts chosen available in a very short time for the races," Zeelenberg confirmed.

"Because the chassis they don’t make over two weeks basically, it's one month's work.

"But if Yamaha already have all the materials available then it doesn't matter to start in Qatar and decide which chassis we're going to use, or which materials."

Helping the four Yamaha race riders will be new test rider Cal Crutchlow.

"First of all his communication is quite precise, so Cal knows how to say things, sometimes not always the good way!" joked Zeelenberg, who helped Cructhlow to the 2009 World Supersport title. "But especially when you come to the bike, he's very precise and he's not shy to say if something is really bad but also especially when something is really good. He really points it out straight away. And of course his speed is there, if you have just stopped from MotoGP, and especially the way he trains because he's always very fit.

"We wish we could ride a little bit more because with the Sepang test cancelled we would have liked to have him on the bike a little bit earlier so we had earlier information. Because now it's very tight for the season. He has all the experience from the Honda, how that bike rides and needs to be ridden – that will be important for us to understand where we stand."

While engine design is frozen, all Yamaha riders will get some form of performance boost simply from having all of their engine changes available this year, after being forced to park some engines due to the valve problems in 2020.

However, Zeelenberg isn't sure how big a difference this will make, other than calming the nerves of the team.

"Good question. It's difficult to answer. Of course we had our restrictions during the season because of [the valve problems] and also Franco at the end of the season was riding with an engine mileage that we could not think was possible to do! This is an understatement I think! And still he was winning races with that engine" he said.

"But that also says that it's not just power and performance but also the electronics, chassis, tyres need to work very good together and then if your engine is a little bit over milage or not it doesn't say so much. But of course it makes you a little bit cross the toes [nervous]… I hope everything goes well.

"But difficult to give an answer. The restrictions will be gone because we had some rpm limitations but even that didn’t really bother us so much because the engines are revving so high that a few hundred rpm less is not going to make a time difference."

While Petronas team principal Razlan Razali was open about friction in some areas of their partnership with Yamaha last season, including the slow arrival of upgrades to help Quartararo retain the title lead, Zeelenberg insisted all is well on a technical level.

"I don't share that feeling basically, I think we get treated very well by Yamaha but of course the bottom line is we are a satellite team, we rent the bikes, but when I look to the technical situation we get all the support from Yamaha they are able to give us," said the Dutchman, who moved to Petronas from Yamaha at the end of 2018.

"So in that sense I have a different opinion than Razlan, but that could also be in the way the discussions are going on, when it's coming to the financial side where I'm not involved.

"The technical side, they give us all the support there is, and on the financial side it's up to him. Of course then sometimes these discussions they go hard, when it’s about money everybody changes a little bit! And of course the situation last year was not very good for Yamaha, because the pandemic and nobody was selling nothing. So also they had to think about their own position.

"But I don’t want to go too deep into that. I feel we were treated well, especially on the technical side."