been told HPI tires gave more grip than PL on asphalt, at track i race at PL tires are the VTA spec only tire now, so far pre-softening works best prior to race day, which consists of putting tires in bags, spraying WD, PB or LW and sealing bag along with placing them in the sun. so far using foam, TC, and buggy traction compounds seem to have little or no effect, saucing the tires prior to a race, even wiped clean for us has proven to be a big mistake. first 4-5 laps are near slip and drift mode.
if you don't do a 1 year phase out, people will go to every corner of the earth to find and hoard them and racers will still have them 6 years from now.