I have usually run tires down to around 3/32" before replacing them. I believe that the wear bars that indicate "worn out, time to replace", are at 2/32".
Yesterday when I was driving home from Colorado, a man gratuitously inserted himself into that discussion while I was getting gas in North Platte, Nebraska. He just walked over to my old Lincoln Aviator, bent down to look at the tires, and told me that I was running them dangerously bald. I thanked him, all the while wondering what the heck his deal was, and told him that while I appreciated his input, I was planning to replace the tires within the next 60 days and figured I'd just run them the last 2,500 to 3,500 miles before they went off to old tire heaven. He seemed quite concerned, unnaturally so it seemed to me, claiming that just by driving on them, I was creating an unnecessary danger to myself, my passengers, and anyone who I might pass on the road. Again, I thanked him, and drove back to I-80 and headed East for the last half of my trip. That was the first/only time I've had someone approach me like that who didn't want either a ride, a handout, or to try and sell me something. Weird.
