Just hit the 2000 mile mark on my Continental Gatorskins. I was just wondering, is there a general mileage where tires should be replaced? I weigh about 160, ride on city streets that don't have many potholes or shards of glass, keep the tires around 110-115 PSI, don't skid at all (maybe once or twice because I had to), and keep my bike indoors away from the elements. The rear tire looks like it's squaring off a bit. Any advice would be greatly appreciated - thanks.