I've read somewhere that you should change shoes approx every 400 miles can't remember where I read it, however like most other people mine have probably done closer to 500 miles. I always work off if you start getting niggles in your legs and back then its time for a change or if the tread is worn out at the edges.
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Having said that I've probably done nearer 500 in mine and they are as comfy as the day I bought them (Brooks stability)
I'd work on the basis that they should get you through a season if you're training for sprint races mostly
jazdog
jazdog