So far in my riding 'career', I've had 2 flat tires, and both were with tires that were just about worn to the wear bars, so it wasn't worth just replacing the tube. I'm pretty anal about tires, I check pressures at least once a week and look over the tread area to see if any cuts or other damage has occured, and every couple of weeks, I spray a soap solution on them to check for leakage.