There has been a reference to a magazine article posted on Corvette websites lately that states the 7:42.9 laptime was recorded after 2 weeks of suspension tuning and tire changing before Magnussen drove the laps. It states that the tires used were treaded street tires, but does not make mention of runflats. I am suspicious that the car tested does not reflect the stock suspension settings and tires...

On the other hand, I'm not aware of any other street tires that are made in the Z06's sizes, so I'm not sure what to conclude...