The most obvious sign of wear on your running shoes is the sole. If the sole and treads are worn down, meaning they're smooth instead of textured, it's time to replace your shoes. Excessive wear on the upper, like fraying on the outside, can also signal that your running shoes have reached their maximum lifespan. Uneven wear can also be a sign that you're wearing the wrong running shoes for your gait—excessive wear on the front is usually a sign of overpronation while wearing on the outside signals supination.Pain in your joints and knees while running and decreased shock absorption are also telltale signs, especially if these things weren't an issue when you first got your shoes. If you're physically uncomfortable, it's time to get a new pair.