Originally Posted by m4a1mustang

Could just be a combination of the softer sidewalls on the PSS and full tread compared to your old, worn down Potenzas. When you wear tires down you eliminate or reduce tread squirm, so they will feel sharper than when new.

That's what it sounds like to me.

Keep in mind the Z is a front-heavy car with staggered tires. Its bias is towards understeer.