My rear tyre, about a year or so old with a lot of use (dry miles only, so that means it's probably had about 6 months use in total) has developed the beginnings of the old "squaring off". Conventional wisdom means it's time to change it, but what with all the waste in the world, etc etc, I thought to myself "Really, how much longer could I ride this?".
There's got to be a bit more rubber to go yet, so when's the absolute latest you'd change a tyre? I've seen some pretty worn out ones still being used, where the black of the outer layer is worn so much you can see the lighter inner layer (admittedly, I'd change it then)....nothing like that on my tyre yet, so...how long..!!?