I’d be surprised if it’s “only” a few seconds faster than the current model. But if 7.25 holds true you can bet GM will re-run the ZR1 on a day w/ less wind and a pro driver. With lap times in the 7 minute range being just 1% slow means nearly 5 seconds. It’s not hard to imagine a GM engineer being a few % off what a true ring-seasoned profesional could do. But perhaps time will tell.
Just for the fun of bench-racing, a good “street tire” is probably 5% faster than a run flat. A true R-compound is at least 5% better yet, probably closer to 10%. So just assuming an overall advantage of 10% going to an R-compound a C6Z06 could shave more than 40 seconds off its ring time… dropping it into race car sub-7 minute territory.
Obviously that’s just pure speculation and nothing but empty bench-racing, but I think most seasoned track drivers would agree that 10% reduction in lap times going from any “true” street tire, particularly run flats, to an R-compound (something on the order of a Hoosier R6 would probably be appropriate for the 'ring) is conservative, very conservative.
However, since the 'ring has long sections of flat out high-speed running where there’s little/no advantage to the R-compounds perhaps typical gains wouldn’t hold true. Still, even a 5% improvement would have the C6 Z06 in the high 7-teens.
For an example of the extreme differences between street tires and R-compound; my car has stock C5 Z06 suspension other than alignment and front sway bar (T1). I hit 1.39Gs on flat ground on Hoosier A6s. Stock C5Zs are rated at around what .98 on Supercars (better tires than run-flats)?
-TJ