I just replaced my PS2s, backs were bellow the "wear bars" after 15k miles of daily driving, fronts could have lasted another 3K maybe...I replaced all 4 to cut down on the road noise you get as the tires get worn down.
It's been raining for the past week in southern cali and I almost spun out and crashed in the rain on a mild banking turn
traction control saved my
. It prompted me to go buy new tires the next morning
. In my experience you can drive till the thread is nearly gone if you live in a desert, or southern california from april through october...once it gets wet the "wear bar" indicators are there for a reason. Moral of the experience is, you are gonna have to replace the tires either way and you are only extending the inevitable while jeopardizing your safety.