Lots of Tricross gravel-grinding here on hard pack and loose fine gravel bike paths. My Specialized Borough Armadillo Elite tires (700x32c) have been holding up well with never a single flat these last few years. But lately a bit of uncomfortable sliding on tight loose gravel turns with treads getting a little smooth. So is it time to replace with new, or is that a waste of money and hold on until they give out? Just don't want to be caught out there with a failed tire. Also thinking of going to 38's on next replacements.