I've always been on the cautious side, and replaced with about 1/4 remaining on passenger car or suv tires. I've got 9/32's to 10/32's remaining on my duratracs now. The duratracs have gripped really well, but they are getting louder. In a snowless climate, they would definitely have another season in them. I'm tempted to see if they are worth anything. And I like buying tires for some reason, so I'm looking forward to new ones.