The parity battle trying to stop a Mustang walkover

The latest era of parity unrest in Supercars didn't actually start with the introduction of the Mustang earlier this year. It can be traced back to the ZB Commodore, which made its debut at the start of the 2018 season.

While still a four-door body shape, perfectly suited to the Car of the Future control chassis, the ZB was the first Commodore racing car that was based on a car manufactured outside of Australia - and was also a hatchback.

Concerns over the availability of genuine Opel Insignia panels from Germany meant Supercars allowed an unprecedented use of composite panels on the new Holden. Composite doors and guards had been commonplace in the series, and the FG-X Falcon was running a composite rear light bucket thanks to a lack of OEM availability. But the ZB's composite roof and tailgate took it to a new level.

By the Saturday night at the 2018 season-opening Adelaide 500, the Ford and Nissan teams were up in arms. The claim was that the weight saved through lighter panels had been cleverly redistributed through ballast to provide a centre of gravity advantage.

The lobbying, led by Ford squad DJR Team Penske boss Ryan Story, was effective. Composite roof skins and bonnets for the Falcon and the Altima were rushed through homologation and made available in time for the Australian Grand Prix support round three weeks later.

DJRTP wasted little time getting the most out of those composite panels. At the Phillip Island event in the middle of last April it secretly introduced a new-spec exhaust system on its Falcons. External ballast may be banned in Supercars, but a muffler system running what some would deem unnecessarily heavy heat shielding was, at the time, given the green light from the technical department.

In a category so restricted in a technical sense - front uprights are considered the final frontier of freedom - saving weight to run more ballast became a new art form. It wasn't just about heavy exhaust systems, but making cockpit controls such as switch panels as light as possible.

There was always going to be limitations with the ageing FG-X package (above), but the Mustang was coming. And optimising weight distribution was an obvious target.

The other was clearly aerodynamics. When the Mustang broke cover, its swooping nose and huge rear wing endplates raised eyebrows. Could it possibly be legal?

It took 10 burning hot December days at Temora Airstrip in regional New South Wales for the VCAT (Supercars Controlled Aerodynamic Testing) process to reach the desired conclusion, with the Mustang's wild-looking bodywork signed off not just by Supercars, but Holden and Nissan representatives as well. In that moment, the Mustang became a completely legal racing car.

There were no suggestions of cheating, and no question marks over the outcome of the VCAT testing

The first comparative run came at the pre-season test at Phillip Island in February 2019, under the watchful eye of the category's brand new technical team of Adrian Burgess and Campbell Little, both title-winning race engineers in their own right. The signs were ominous; on the fast, flowing layout it was a Mustang top three at the end of the day, along with a sense it could have been worse. Scott McLaughlin, for example, was just eighth quickest, but repeatedly set fastest first sectors throughout the day.

When Autosport asked him if he'd been using a timing beacon elsewhere to keep his cards close to his chest, he smiled broadly and joked "I kept spraying it; driver error..."

Then, when the season kicked off proper in Adelaide, the Mustangs picked up where they'd left off at The Island. Except now everyone was playing for keeps.

No sooner was practice over than the Holden drivers were discussing how quick the Mustangs looked through the fast Turn 8, while DJRTP boss Story pre-empted any parity chat by reiterating that the VCAT outcome was "the closest in history".

Even Ford Performance aerodynamicist Sriram Pakkam, on the ground in Adelaide for the Mustang's debut, was on message regarding the impending parity storm: "It's got to be fact-based, right?" he said when Autosport asked about the whispers of inequality doing the paddock rounds.

"We've gone through a parity process and we've come out level with all three [cars]. I don't know, we followed all the rules, we've followed the regulations, and the rest is up to the team bosses and the sanctioning body to deal with. The ZB was quick last year too..."

There were no suggestions of cheating, and no question marks over the outcome of the VCAT testing. But what was coming to light was potential inadequacies in the VCAT process, which is largely focused on straightline aero performance - not how much downforce is being created mid-corner. It had never been an issue before, but there'd never been a coupe shape to play with before, either.

Four of the six Mustangs finished in the top six in the first race in Adelaide, followed by a Mustang one-two for McLaughlin and Cam Waters on the Sunday. Seeing a clean-sweep from an in-form McLaughlin, driving for an in-form DJRTP, wasn't overly surprising. But the upswing in results from Tickford, which had struggled through 2018, is what really raised eyebrows.

Still, it was the Penske Mustangs that copped the first change. After Adelaide, Supercars responded to a wave of centre of gravity concerns by asking the team to remove those heavy exhausts. Rival teams claimed they were as much as 21 kilograms heavier than required. DJRTP never denied the units were heavy, but refuted the figure.

Regardless of the weight, the units were gone for Albert Park.

Not that it slowed them down. McLaughlin won three of the four races and would have bagged the quartet for the weekend had it not been for his warm-up lap shunt with Waters on the Saturday evening. The first race was an all-Mustang top five, with Chaz Mostert coming from 22nd on the grid to finish fifth. From the 12 podium spots on offer all weekend, only three went to Holden drivers.

The Monday and Tuesday following the Australian GP weekend was spent further evaluating centre of gravity at Kelly Racing's workshop on the outskirts of Melbourne. There were 10 cars used, with Nissans from KR, Mustangs from DJRTP and Tickford, and Commodores from Triple Eight, Walkinshaw Andretti United, Garry Rogers Motorsport, Erebus Motorsport and Brad Jones Racing.

The outcome was overwhelming. The Altima was used as the control, with the Holden teams ordered to relocate 6.7 kilograms of ballast into the ZB's roofline, and the Ford teams forced to move 28 kilograms of ballast to the top of the Mustang's rollcage.

The public reaction from the Ford teams was telling; Tickford said it was "not thrilled" with the outcome, while DJRTP's media release was heavily focused on how the team was investigating an "alternative process" to the CoG test that Supercars had used. Even the way the Mustang's arrived in Tasmania - with the ballast clamped to the rollcage, rather than hidden in the roofline like the Commodore - had a sense of 'up yours' about it.

"Whilst we understand these changes are in the interest of the sport, we expect to run the rest of the season on track unchanged from this specification" Ford's Mark Rushbrook

The Symmons Plains circuit, with its low aero dependency, hinted that the CoG change had indeed had an impact. The Penske Mustangs were quick, but the Tickford Mustangs dropped back into the field. And a Commodore even won a race.

Still the question of aero was at that point still very much unanswered. Supercars looked at breaking its own windtunnel ban and sending cars to Monash University in Melbourne, home of the only remotely suitable tunnel in the country, in between the Symmons Plains and Phillip Island rounds.

But the stumbling block was that the Monash facility isn't big enough for side-on testing, which means it wouldn't have addressed the crucial yaw performance concerns. To get the required data was likely going to require a costly trek to Windshear in the United States. Instead, Supercars opted to stick with CFD and evaluate the data after the return to Phillip Island.

Unsurprisingly, The Island provided another pair of Penske one-twos. And in the Sunday race, five Mustangs finished in the top six.

It took just over a week for Supercars to hand down its verdict of its post-Phillip Island analysis - and, as expected, the Mustang has had its wings clipped. When the season resumes in Perth next week for the Barbagallo night races, the six Mustangs will be sporting smaller rear wing endplates, a lower gurney flap and a shorter undertray.

Again, the Ford reaction was carefully-worded. This time a joint statement was issued with quotes from Ford Performance boss Mark Rushbrook.

"The Mustang is an advanced, state-of-the-art Supercar, designed and built within the rules of the series. We are disappointed that we have had to make changes to the cars, however we respect the Supercars technical department and will comply," said Rushbrook.

"Our car was signed off and homologated by Supercars ahead of the 2019 season, however whilst we understand these changes are in the interest of the sport, we expect to run the rest of the season on track unchanged from this specification."

Those quotes make Ford's position abundantly clear. It's done Supercars a favour by altering what was signed off as a perfectly legal car. But don't even think about asking for more changes, regardless of what happens next.

So, what does happen next? The likely outcome is that McLaughlin keeps winning. He's in a league of his own form-wise at the moment, and, paired with an equally strong Penske outfit, would probably keep winning if he was forced back into an FG-X.

The fan reaction to the entire saga has been emphatic, with both sides of the Ford/Holden divide expressing a sense of being short-changed. But the reality is, there's no one party truly at fault.

DJRTP and Ford Performance handled a set of regulations in a ruthless, yet legal, manner.

Roland Dane, meanwhile, focused his lobbying on the spirit of the category and its touring car roots. The chief of Holden's leading team Triple Eight copped a lot of fan backlash, but his message about avoiding complex aerodynamics is consistent.

In an interview with Autosport back in January 2015, not long after the Gen2 roadmap was made public, he said: "For all intents and purposes, what we want to maintain is the look of the cars in relation to their street counterparts. I believe we've managed that better than any other touring car category by a massive margin, because our cars don't have silly bits of aerodynamic stuff all over them, they don't rely on massive aero, they don't have crazy wheel arches that make them look like a Saturday night special that was done in Birmingham in a back street."

And Supercars? Yes, this has exposed issues with the VCAT testing, but trusting a system that served it so well through the four-door era is forgivable.

As is always the case with aerodynamics, the genie is now out of the bottle. A trip to a suitable windtunnel seems, at some point, inevitable... particularly if there are new models, and more two-doors, on the way as soon as 2021.