About a Specialized Stumpjumper FSR from around 2000 (meaning the 2000 model year, not the 2000s era),
when the seatpost length is adjusted to stick out just slightly from the frame,
the front shift outer cable (depending on its length)
sometimes interferes with the bottom of the seatpost,
and after years of use in this condition, I've seen
the aluminum seatpost bottom get worn smooth
as if someone had run a round file along it—
the size of the outer cable's diameter.
Strangely, the outer cable itself wasn't worn at all.
It's not that the outer was also being worn but had just been replaced
by the time I saw it.
I happened to remember that story today,
because I was servicing a flat-bar hybrid bike with
hydraulic disc brakes and mechanical shifters,
where the outer cable routing order was poor
and the outer cables were pressing against each other in contact.
At the spot where the shift outer cable and brake outer hose
were constantly rubbing hard against each other,
the shift outer cable's housing had been worn away,
but the brake outer hose was completely fine.
If it had been the other way around, there'd be a risk of brake fluid leaking,
so this is clearly intentional—soft file wins!
While writing this, I remembered one more thing.
In the case of front caliper brakes (→here), the outer also comes out on top.
The story linked there about "the seatpost getting worn from rubbing against the outer in the Ohtaki 1 race"
is not from the Stumpjumper mentioned at the start, but from a Gary Fisher Excalibur.
when the seatpost length is adjusted to stick out just slightly from the frame,
the front shift outer cable (depending on its length)
sometimes interferes with the bottom of the seatpost,
and after years of use in this condition, I've seen
the aluminum seatpost bottom get worn smooth
as if someone had run a round file along it—
the size of the outer cable's diameter.
Strangely, the outer cable itself wasn't worn at all.
It's not that the outer was also being worn but had just been replaced
by the time I saw it.
I happened to remember that story today,
because I was servicing a flat-bar hybrid bike with
hydraulic disc brakes and mechanical shifters,
where the outer cable routing order was poor
and the outer cables were pressing against each other in contact.
At the spot where the shift outer cable and brake outer hose
were constantly rubbing hard against each other,
the shift outer cable's housing had been worn away,
but the brake outer hose was completely fine.
If it had been the other way around, there'd be a risk of brake fluid leaking,
so this is clearly intentional—soft file wins!
While writing this, I remembered one more thing.
In the case of front caliper brakes (→here), the outer also comes out on top.
The story linked there about "the seatpost getting worn from rubbing against the outer in the Ohtaki 1 race"
is not from the Stumpjumper mentioned at the start, but from a Gary Fisher Excalibur.