Hazelwood and primary driver Brodie Kostecki achieved the rare feat of backing up last year’s Bathurst 1000 win at Erebus Motorsport with a first-up enduro triumph at Dick Johnson Racing.

But amid the move between teams, there was a not-so-obvious rule change that Kostecki highlighted post-race amid praise for his co-driver.

“It’s awesome to be partnered with this guy, he’s the best co-driver out there,” said Kostecki while standing alongside Hazelwood amid the victory celebrations.

“I feel really privileged to be driving with him. It shuts down a lot of the weight stuff for him at Bathurst last year, he was ‘lights out’ on all the other guys.”

The “weight stuff” was a reference to the driver weight rules that caused controversy in recent enduro seasons and benefitted the likes of Hazelwood.

Previously, the minimum car weight rule of 1340kg utilised only the weight of the primary driver and their racing apparel, even for the endurance races.

That meant any co-driver lighter than their primary was able to complete their stints in the endurance races with an underweight car.

The issue was raised off the back of the 2023 enduros, where the mismatch combinations of Shane van Gisbergen/Richie Stanaway and Kostecki/David Russell set the co-driver pace.

Despite it being slammed as an unfair advantage, Supercars elected not to act for 2024 – citing the fact teams had already signed co-drivers with those regulations in place.

Hazelwood was among those to benefit most last year when teamed with Kostecki at Erebus. According to Kostecki, Hazelwood was driving 22kg under the minimum weight in 2024.

While estimates on the exact lap time benefit vary, Supercars acknowledged that some were enjoying a “significant advantage” over the course of a stint at Bathurst.

For 2025, it revised the rule to utilise average weight.

In cases such as Kostecki and Hazelwood where the primary driver’s weight is greater than the average of the two, the 1340kg minimum car weight applies using the average figure.

And where the primary driver’s weight is less than the average of the two, the 1340kg minimum car weight continues to utilise only the primary driver figure.

The end result reduces the advantage enjoyed by the lighter co-drivers, while not allowing the lighter primaries to run under 1340kg.

In the Kostecki/Hazelwood example the delta between them is essentially halved; the co-driver gets half to run underweight and the primary is slapped with the other half to run overweight

“Todd with his kit and seat insert is 92 or 93 [kg] and I’m 105… so I’ll drive around five or six kilos over the minimum weight,” Kostecki said via Lucky Dogs ahead of The Bend.

“I’ve been trying to trim down, and he’s fattened up,” Kostecki added. “Every time he’s been into the workshop there’s caramel slice…”

The notion that lighter co-drivers could help their primary by gaining weight this year was not limited to the Kostecki/Hazelwood duo.

Among the other combinations with significant weight disparity is Erebus Motorsport duo Jack Le Brocq and rookie Jarrod Hughes.

“Jack has been telling me to go to KFC every day,” laughed Hughes at The Bend. “He said I’ll give you some money for a KFC bucket, just go and fatten up for me!”

The new rules have been criticised for impacting the primary drivers, who spend the bulk of the races – including the key stints at the end – in the cars.

It’s an issue that’s also experienced in GT endurance events such as the Bathurst 12 Hour, where weight is averaged across three or four drivers.

“It’s a tough one, there’s no real perfect answer,” surmised Triple Eight team manager Mark Dutton, whose squad was among those to support the rule change for this year.

“Sometimes it is just trying to make the best compromise so that no one is massively advantaged or disadvantaged.”

Supercars rules continue to stipulate a minimum driver weight of 95kg (including race gear), meaning cars with either their primary or the average driver weight under that figure are fitted with ballast inside the cockpit.

There was no change to the rule this year regarding qualifying, where only the weight of the driver at the wheel during the session factors into the 1340kg, regardless of their co-driver’s status.