Internal routing of cables - liner...?

[Frank9755]

My old bike, which used to have Di2, has internal cable routing.  I'm now re-building it up with cables (the Di2 bits having been cannibalised for my new bike).

When doing my pre-project shopping I got some white cable liner - ie the thin stuff, not strong like cable housing.  But do I need it, is it advisable / optional...?
If I do need it, how much do I use - as much as possible, right through to the mech - or just a little bit where the cable goes under the bottom bracket? 

Or does it depend on the inside of the specfic frame?

ISTR recall when I bought the frame 8 years ago that it may have had some of this stuff in it then, but I didn't know what it was and thought it was just a form of plastic string to guide cables through. 

[Hot Flatus]

If you've got one of the more recent Shimano front mech you can run the outer all the way to it.

[Dickyelsdon]

For frames that have cable stops at the frame entry points (i.e dont use outer cable for the entire length) its usually just there on new frames to make it easier to run the cables in the frame, no fishing required.

Most of the liners wont fit inside cable outer anyway uneless its specific stuff. So you'd have to cut it back to not interfere with the outer cable.

You only need it if there is any contact with the frame, which there shouldnt be really, other than the BB. If you need it at the BB depends if there is a plastic cable guide there. Many frames still offer one for internal routing, just like the ones installed under the BB of normal frames.  Sometimes these are removed to install DI2 so check you are not missing one.

[Frank9755]

I have a cable guide under the BB. I thought it might be good to use it there as it gets pretty dirty.

I also thought that it wouldn't do anything inside the down tube, but there seem to be some internal walls inside the tube. Not sure if these are structural or just messy bits of carbon residue. If the former then sawing them with gear cable might not be the best plan, but it's probably just carbon mess!

The cable stops are plastic inserts that fit into the frame holes.