I did today’s run session with Nathan who tracks his mileage with his Ipod Nano which prompts me to suggest this as a good idea. You could use a Nano or a Garmin or could work out your pace and calculate the mileage yourself. It doesn’t need to be particularly accurate but it will let you know when you should buy a new pair of running shoes.
Typically shoes won’t look knackered even when they are. The heels and soles will only show a little wear but the constant pounding will have “crushed” the mid sole and you won’t be getting enough cushioning. The eventual result of this is that injuries caused by jarring will occur. I suggest buying a new pair of shoes when your current shoes have covered about 350 miles, this then allows you to alternate them. Alternating shoes is another good idea if you run day after day as you shouldn’t run in the same shoes two days running. Letting the shoes “rest” for 24 hours after a run allows them to recover from the run and get back their bounce. Doing this regularly extends their life and helps prevent injuries.