Originally Posted by MaysEffect

Were you measuring tire pressure consistently?. Given the natural weight balance of the car, its possible the rears are just moderately scrubbing during turns. This is not unusual with front weight biased vehicles.

As a cheat/penalty, carry an extra 40-70ibs in the rear. Of course strap whatever it is down as best as possible. as far rearward as possible as well.

You don't have to burden yourself with this practice indefinitely, but just enough times to gauge how the tires react to a slightly rearward bias change. The GVWR accounts for a load range of up to about 200ibs. And additional load on the rear can keep the tires from sliding and scrubbing the surface. Downforce