Originally Posted by
noglider
We replaced cable housings down there with bare cable because the housings had a way of sucking in water and grit. These thinner tubes might not be as bad, but bare cable still may be best (or least bad).
+1 ^^
I've seen many incidences of various tubings ending up doing more harm than good, especially where something slips out of place along the cable's path, causing a loss of cable tension adjustment.
I typically just put a drop of chain lube on each cable path whenever I lube my chain.
A bolt-on plastic cable guide piece is better, and in a couple of cases I used the existing guide loops to retain a short, thick section of rather stout plastic tubing.
Trek used stainless-steel cable sliding plates under their carbon frame's bb shell which actually caused enormous friction against stainless-steel cable, but luckily the plate's retaining tabs could be crimped onto some thick plastic tubing so as to retain a short piece of it (so not to lose indexing adjustment later because of a drifting piece of tubing).
A couple of Italian bikes I've seen had stepped, very sticky cable pathways under the bb shell, and luckily here I was able to force a right-sized diameter of plastic tubing into the existing loop(s) so as to eliminate the severe friction problem.