So bought some used sneakers about three years ago, we've worn away about half of the remaining life in that time. Half inch worn down to 1/4 or so above the TWI marks. They have a few areas where there are no cracks. I figure when they start loosing air then it'll be time to replace them. I was wondering if they had a date code branded or encoded, or do I contact Michelin with the serial number to find out? Just to make a good argument, it sounds like if we burn off 6/32 a year, then maybe get 7 years out of a set.