And how do you decide when to retire them?
I used to abide by the 300-mile rule - many years ago (10?).
Then I started running in Newtons, which seemed to last between 4-500 miles before retirement.
In recent years I have switched to Altras, which seems to depend on the model. I had a pair of Ones that barely made it to 300 miles. Then I went through three pair of Escalantes, which each got an easy 400 miles a pair.
For trail running I tried some Newton Bocos, which got over 300 before I retired them for other reasons.
Then I blew through two pairs of Altra Superiors, which seemed disappointingly frail for trail runners.
I look at red wear, but more importantly, soul cushion, to determine if a pair of sneakers is spent.
The Escalantes are my favorite road runners ever. I could probably get more than 400 miles out of them, but like to avoid injuries. (Plus they make nice house slippers in retirement. Trail runners get put on lawn-mowing duty.)
I was going to say 200-300. unfortunately, I 'train' mostly on sidewalks and streets, which, imo, does a job on the cushioning as well as tread.
I found I had have at least two pairs, one for training, one for the 'real trails', else my training shoes were always in need of being switched out before getting into the wilderness/hills (as I want the max support/cushioning I paid for!)
Late to the conversation, but I always stick to the 500 mile rule, unless I determine the shoes have taken too much. If I waited for tread wear, I'd probably hurt myself! Definitely cushioning is my sore spot. If I feel anything significant or a glimpse of pain that's it. I separate shoes based on the length of run too. An older pair may be no trouble for a three mile run, but if I'm out for 10 or more, I want the most cushion possible. I rotate pairs too so that the cushion has time to "plump" between runs. That could sound like a big investment, but I'm always searching sales racks and trying new things since every time I find "the one", they stop making it. The replacement usually is not the same... Also, as new pairs get worked in, I have a good comparison for what the cushion Should feel like since you never notice the decline.
While I do track mileage on my shoes via Strava, like others here, I really don't think there's a solid rule of thumb on miles. I have had shoes from the same brand vary widely in the mileage I could get out of them. For me, it has typically been anywhere between 300 and 600+ miles. I find that, if I listen to my feet and my knees, I go off that to determine when to retire shoes. I also like to rotate through a couple different pairs of varying styles. Yep, I am shoe nerd (as much as I can afford to be anyways).
I hardly ever get more than 250 miles out of a pair of shoes. I run in Adidas, Brooks, Mizuno, Nike, Saucony and Salomon currently. All neutral-cushioned shoes. I am on roads 99% of the time.
I always figured I'm harder on shoes than most runners because I would wear off the outsole in the heel after 300 miles. 500? I would fear I'd wear off half the midsole.