Motorsport.com understands that both Tickford Racing's Zak Best and Image Racing's Jordan Boys on a different batch of the soft compound Dunlop rubber as the rest of the field.
That's likely to be related to production schedules.
While the compounds are the same, the fact the tyres are from a different batch has led to some angst in the Supercars paddock.
That was heightened when Best stormed to a sensational pole position in qualifying for the opening race.
Boys, meanwhile, was a credible 17th in his Erebus-backed entry.
"There's a huge difference," one driver told Motorsport.com. "I've been told that the teams that tried those tyres from that batch at the test day were six to eight tenths faster."
Tickford Racing boss Tim Edwards said it was impossible to tell if there was a difference given there was no opportunity to back-to-back the two batches.
He also pointed out that Best had out-performed Boys to an extent that made his pole lap impressive even if there was a tyre edge.
"We don't know what we don't know," he said. "If they are just running on those tyres... it's not like we've had the opportunity to back-to-back them.
"Jordan had the same tyre and he was over a second slower. Zak still did a good job. There may be a difference but that's just speculation.
"Even if there was some difference there, the reality is that he still drove the lap. He's been fast all day, even on his practice tyres, which were from a different batch because everyone's pre-marked tyres are from different batches.
"He's doing a solid job."
