65# max would give you a "D" rated 8-ply equivalent tire. The door jamb still applies as a guideline as your entire suspension system is designed around the amount of flex/spring rate the factory supplied tires had @ that pressure. If you've got a 1/2T that came with 4 or 6 ply rated tires, the 8-ply you have now will ride a little stiffer, even @ door-jamb pressures. If you have a 3/4T or 1T pickup that's supposed to have "E" rated 10-ply, those 8's are gonna feel squishy.
