I have at least two pairs of each shoe on the go at any time, sometimes three.
I try to avoid running in the same pair of shoes on consecutive runs, just to give them time to breathe and/or dry, and it spreads the wear around. But mostly the idea is that you don't want to be doing long runs in shoes nearing their end of use, nor with shoes right at the beginning of their life, so new shoes are worn in a bit and then favoured for longer runs.
(The trail shoes are often worn when it's wet or, for my local parkrun, runs that can involve running through 6" deep puddles and thick mud. Giving them at least a few days to dry off is a good thing. I never clean them, the mud just falls off at the start of the next run.)
Strava keeps track of the total kilometerage of each shoe for me. I don't bin them at any particular distance. The Saucony Jazz 17/18/19/20/21 I use for general running tend to start to fall apart in some way at about 800km, usually the tread wears out like this (and are retired to casual/garden usage):
(yes, I was running in those until that point, I'm lucky that I don't get injuries because of this but I'm guessing this is more to do with playing years of 5-a-side football means my muscles are better developed for dealing with non-lateral movements that are often the cause of injuries in runners.)
Looking at current shoes on Strava:-
* Saucony Peregrine 4 SS14 Oct14 Green - 800.7 km
* Saucony Peregrine 5 AW15 Jan16 Blue - 564.8 km
* Saucony Jazz 21 Blue - 32.1 km
* Saucony Jazz 18 Sep16 Yellow - 396.3 km
* Saucony Jazz 17 AW15 Nov15 Red - 593.8 km
Almost all of my shoes are previous years models bought in sales for 50% off. With shoes with an RRP of £110 or so this makes it considerably cheaper. It also helps that I'm not chasing the latest Nike AirFly Max NEXT% nonsense (those retail for close to £300!?!).
800km out of a pair of shoes would mean 70 run commutes. For a ~£60 shoe (bought in a sale) that's just under £1 per commute, not bad compared to the train (£2.60 off peak) but more expensive than cycling.
The Peregrine's are the trail shoes and they look like they'll last a lot longer than 800km, I reckon probably 1600km before the cushioning is completely gone although I should look to pick up a new pair in any sales as a replacement should the trusty green pair start to go.
