Question - should the discs not last until they are 100% worn?
This is 100% wear
But yeah if there is 60% left until the recommended manufacturer limit he's only about half way through. If he's had it from new, then double the current mileage and he's got an easy estimate of when to replace them.
He has new ones on now. I think 70000 miles on the originals - the ones worn 40%.
I don't like spending money (he is worse than me!) and I would not be keen on spending money on something that wasn't at least 80% worn.
This is 100% wear
But yeah if there is 60% left until the recommended manufacturer limit he's only about half way through. If he's had it from new, then double the current mileage and he's got an easy estimate of when to replace them.