Turtle Wax Trans Am Series Category Management is investigating the controversial droop in the rear windscreens of the Garry Rogers Motorsport cars.

A furore has broken out in the series over the droop in the rear windscreen and roof line which the three GRM cars, all Ford Mustangs, exhibit.

Notably, Mustang-bodied cars of different generations entered by rival competitors do not feature the droop.

It is thought that the deformity in the GRM cars leads to a greater volume of air flowing over the rear wing, and hence an increase in rear downforce, all other things being equal.

A statement from the category in response to the controversy reads, in full, “Category Management has been made aware of the issue and are investigating with our technical partners and Motorsport Australia on why this may be occurring and if any changes to the Technical Regulations are required.”

Two of the GRM vehicles in question are driven by Nathan Herne and Owen Kelly, who are positioned first and second in the series standings, respectively.

They locked out the front row for Race 1 of last weekend’s Queensland Raceway round, with Wall Racing’s Tim Brook a further six tenths of a second off the pace in third position, although photographs show the droop in at least Herne’s car at previous rounds of the current season.

It is particularly pronounced in the #45 GRM entry of Lochie Dalton, but absent from Car #03 of Ben Grice and Car #69 of Jon McCorkindale, for example.

Worth noting is that Grice’s car is of latest spec, being a late-2021 build, whereas McCorkindale’s is a 2018 build.

Those facts are pertinent given one theory that the GRM issue is in fact a broader one related to a particular generation of car/bodyshape.

While it should be stressed that there is no confirmation that GRM is in breach of National Trans Am Series regulations, NASCAR Cup Series teams have fallen afoul of officialdom for failure to maintain rigid rear glass in recent years.

In 2018, Kevin Harvick’s win at Las Vegas was excluded from Playoff consideration, with he and the #4 Stewart-Haas Racing entry stripped of 20 series points, for what was deemed a Level 1 breach.

Crew chief Rodney Childers claimed that the bend in the roofline and rear windscreen which occurred at speed was inadvertent, and had been caused by a failure of a rear window brace.

That explanation squares with a theory from a Speedcafe.com source, who explained that the rear windscreen bend could be caused by a failure or looseness in the brackets behind it.

The sixth and final round of the 2022 National Trans Am Series takes place at Sandown on September 16-18, before the Trans Am 100 at the Supercheap Auto Bathurst International in November.