How long will they do me Dermot? When will I need to change these again? What sort of mileage are in these babies?! These are all questions that I regularly get in relation to the life span of a pair of running shoes. The fact is that most of the running shoe company's will recommend that you change your shoes post 500 miles of running; after this the foam in the sole unit will become more compressed and so lack the required cushioning which provides the impact protection