You can take the shoes that you’ve been running in and look at them from behind. If they are starting to wear out, they will not sit flat. You can see the wear on one side. However, your shoes may be starting to break down from the inside even before the outer soles show signs of wearing out. The cushioning on the inside of the shoe which keeps your foot stable and protected will usually break down before the outer sole. Wearing shoes that are broken down can cause injuries if run in for many miles.
The general rule of thumb is to replace your running shoes between 300 – 500 miles. How soon they break down depends on your body weight as well as the surfaces that you run on the majority of the time. Also, how your foot strikes the ground can be a factor. If you are a heavier runner – you should be replacing your shoes around 300 – 350 miles. Lighter runners can usually get 450 – 500 miles from a pair of shoes.
Be aware of any aches and pains when you run. This could be a sign that your shoes are needing to be replaced. Another test is the twisting test. If you can twist your shoe, it may be breaking down. It should be firm.
Keep track of the mileage on your running shoes in your running log. Whenever you write your run in your log, in addition to the usual entries (weather, mileage, course, etc.), write down which shoes you ran in.
Also, you should have 2 pair of running shoes that you are running in at the same time. Rotating your shoes can also prolong the life of them. Wear one pair and then the next time you run – wear your other pair. This will allow each pair to thoroughly dry out on the inside before you wear them again. Even if it is not raining, your feet sweat and will make the inside of your shoes wet.