The 800km rule is not a measurement
It is a rounded average that suits retailers. Across our test data, useful midsole life ranged from 240km to well over 600km depending entirely on foam chemistry and rider mass.
Check durometer drift
A midsole that has softened by more than ten points from new has lost most of its useful rebound. You can approximate this at home by pressing a thumb into the lateral heel and comparing against an unworn pair in a shop.
Check outsole loss
Once you can see midsole foam through the heel strike zone, the geometry has already changed. That matters more than the tread itself.
Ignore the upper
Uppers usually look worn long before the midsole is finished, and occasionally the reverse. Neither tells you much about the part doing the work.
