As title really. Mine discs have done approx 4-5k miles. Still look fine but wondered when or if ever they wear out?
If you run your fingernail from the spines to the braking surface you might find the braking surface is more worn.
At that point I change mine but it takes a lot of use
The only time I've ever needed to change mine is when I've either managed to warp one or when I've wanted to change for purely aesthetic reasons. They do tend to last for quite a while notmally.
shimano have a minimum thickness on them.
I would replace when they get to this thickness or they have lots of scoring or uneven wear.
I have a Hope floating disc that wafer thin, I decided to change it before it fell apart on a long decent. It's the only disk I've ever felt the need to change
As z1ppy.