Originally Posted by 79pmooney

Pump the tires up hard (110 psi) and see how long they hold pressure. 6 hours later you certainly should have 100 psi. (The fact that you are seeing bubbling doesn't sound good to me, but give it a try anyway.) If there is a leak, bubbling will always occur at the valve and any cuts through the casing. If there is no bubbling elsewhere, see if you can hear the air hissing out somewhere besides at the valve. That would be the problem. Mark the casing there for future reference. Those tires look to be in excellent shape and are good quality. Someone will want to fix them if you don't.

Ben