The last-minute change is the result of centre of gravity testing undertaken by Supercars with the Camaro, Ford Mustang and Toyota Supra in Bathurst last Sunday and Monday.

Supercars has crunched the numbers and determined the GM teams must wrap 4.4kg of ballast around the roll-cage tube directly above and forward of the passenger seat area.

Downplaying the significance of the adjustment, category motorsport boss Tim Edwards said Supercars tweaked its usual testing procedure this year.

“We did a more detailed version of what we’ve done before,” Edwards explained.

“In the past we’ve actually had more cars, but then you end up with a big spread of that’s got a new bumper, that’s got a used bumper, that’s got a new rear guard, that’s got a used rear guard.

“To be more clinical, we had three cars, all with brand new bodywork, we took all of those individual panels off the car and weighed them, so we were 100 percent confident exactly where they were.

“Obviously, that highlighted that there was a small difference.

“It is only a small difference, we’re talking in millimetres, but actually then the translation is you’ve obviously got to put that into kilograms to make the change, but in millimetres, we’re talking a small amount.

“The GM guys have made that tweak to their cars.”

Parity is again set to be a big talking point this season with Toyota joining the fray alongside Ford and Chevrolet.

While the top Toyota was just 16th in Wednesday opening half of the pre-season test, Edwards said little could be learned from the running.

“Everybody was keeping their powder dry for tonight,” he said ahead of the Thursday night session on the full track layout.

“Yesterday you would run on your worst tyre. Tonight we’ll get a better read of where everybody’s at.”