My first thought was right there with Carls. Rubber gets harder with age and therefore looses grip. Two good signs of the tire getting hard which I have learned first hand are.
1- the tire starts to feel like it wants to slide every time you make a corner even on dry pavement. I even had the entire bike slide sideways on a ramp one year coming home from a WNY rally, to which the Count, who was behind me witnessed. Thankfully I did not go down but it was a wake up call
2- You start to notice that tire wear slows down and begins to exceed its normal life span. Initially you think great, but then you come to realize there is a very bad reason for this extended tire life.
Even though the tire has lots of tread left, when it gets to this point change it. THE HIDE ON YOUR RIM IS NOT WORTH THE HIDE ON YOUR BACK .
Hey @cowpuc I think I just made up a new slogan for your collection.