Both cars logged 1.5 seconds to 40 kph, look at the slalom data and C lap time. There's nothing to suggest that the PSS were not working well. Ask anyone who's driven summer tires in freezing temps -- when they're "off" they're really off. You're hoping to make the stop sign, not collecting acceleration and slalom data. Sport Auto wouldn't have tested the C if the tires weren't functional.
Some of the contributors here haven't spent a full day at the track, or tracked in wide-ranging conditions...
In mid-summer, the difference between morning and afternoon sessions is regularly 20 - 30 F. Provided you get the car/tires dialed in during the a.m. hours, you cannot hope to match morning lap times once temps are in the upper 80's and 90's in the afternoon.
The difference between PSS/PS4S and (Star Spec) PSC2 over one hot lap is maybe 1 second, perhaps less. Some of you guys are vastly overestimating BMW's version of the Cup 2. It's street-friendly, good wear, not in the same neighborhood as the R (
https://www.tirerack.com/tires/tires...+Sport+Cup+2+R). The difference is not like previous gen tire upgrades, e.g., Pilot Sport PS2 to Nitto NT01.
The difference between 90 degrees and 30's is at least 1-2 seconds a lap.