a. What? Why would i replace them?
b. When my dog has chewed them up.
c. When they stink too much to stay in the house.
e. None of the above.
The general wisdom says to replace running shoes after 300-500 miles. What happens when you don’t run that much or don’t track mileage that closely?
Shoe cushioning and the materials that make up a running shoe deteriorate over time. Coach likes to write a date under the sock liner so that she’ll have an easy way to tell how old a pair is. If you tend to run 20 miles per week, after 6 months you will have 500 miles on your shoes. Time to switch them out. If you run more and/or have a heavier build, especially if you are training heavily for a goal event, you will generally need to switch your shoes more often.
Often you can tell that shoes are wearing out by noticing little aches and pains in your feet, legs and hips. They may not fit as well as the materials change with degradation. Before panicking about injury, think back to when you last replaced your shoes. A pair of shoes is cheap compared to a running injury!
Certainly if you wear though the outer sole of your shoe, you should replace them. The outer sole is made of a tougher material and exposing the softer under sole can easily change the mechanics of the shoe which could lead to injury.
You may have heard that switching between multiple pairs of shoes will extend the life of a pair. There is no evidence to support this but it never hurts to have a spare pair of shoes to switch to if your current shoes get wet, if you need a pair to keep somewhere else or just because you like shoes!
Also you may try different types of shoes depending on your training day. For instance, for those easy recovery runs, you may want your most supportive shoe. If you have speed work or a race, contemplate a lighter shoe with less support. it can be fun to have “fast shoes” as long as you have no injury issues that would contraindicate this. Many athletes find they prefer one shoe and there is nothing wrong with that.
And don’t forget that what you wear on your feet all the other waking hours when you aren’t running can wear out too. If you use custom or over the counter orthotics, those also can show wear and deteriorate over time.