I've always wondered why the standard for derailleur cable routing under bottom brackets is to not use any cable housing. In the past, I have seen others slip the cable through a very thin housing material then into the bottom bracket cable guides when there are no plastic cable guides. This, I'm assuming, helps the cable slide freely and also protect the bottom bracket paint and shell.

Example:


Fantastic! I'm in. But where do you buy it from!? Everyone I ask seems to "have a little" in their shop but nobody knows where they purchased it from.

I just did a build, will try to find pics as soon as I finish typing. That cable roughing, cable on metal drives me nuts. On such a otherwise fine bicycle, its almost like the builder cut corners. And yes, the cable eventually does saw away the bottom bracket slowly but surely. I got a few pieces from a local LBS, I help out there, but the owner treated it like gold, and gave me about a foot of it. Is it inner housing liner? On another note the pic above, can you really fit a water bottle in there? Would someone want to?

I save all the tubing that comes in internal routed frames...not sure where it comes from. I bet McMaster would have it though.

Vintage Trek racers were/are metal-to-metal. My '86 760 surprised me when I first flipped it over on initial cleaning. I put a dab of grease on it and clean it frequently to help it along.

I have found that the tubing for automotive rear air shocks is perfect. It's black, very tough nylon material, perfect size, works perfect. I've seen it in white or black. One small roll will last for ever. it's comes in a few sizes, get the small diameter. You can also go to the LBS, they usually have a small box full.

You can get it at Amazon: https://www.amazon.com/Jagwire-Black-.../dp/B0029LF1XO

Does anybody know that it actually helps the cable slide or does it just protect the paint?

Try heat shrink tubing.

I grab a handful off the floor ever time I build up a bike at work. White is for DR cable, black is for brake cable. I use it for my 89 Trek and the few bikes that have an exposed cable along the top post.

Try your LBS.. they may have lengths of teflon cable liner such as this or the black mentioned above that they sell by the foot. Or buy a foot of line cable housing and use the liner from that.

Both of my road bikes with under-the-bracket cable routing had Teflon guides.

Since my 1959 Capo was designed for a front derailleur with an integral cable stop, I had to improvise when I installed a newer unit to replace the worn-out Gran Sport (which looked just like a Valentino, and similar to a Simplex, with a pushrod and a square box behind the seat tube). I ran a length of Campagnolo stainless cable housing from the downtube-mounted stop under the bottom bracket, and just let it terminate vertically in mid-air. Works like a champ.

Some tubing under the BB definitely helps the cables slide easier. On one of my frames, the metal cable guides under the BB were not aligned properly and it was difficult to shift when my LBS first built it up. I asked him to install some tubing under the BB for the cables, and it shifted great after he did so.

From heat shrink tubing, automotive rear air shock sleeves to official Jagwire black housing liner, it proves there is certainly more than one way to skin a cat (great expression, don't you think?!).

I'll likely go with the Jagwire tubing just because, although the other options are clever and possibly better material, the Jagwire product is made for this application. Plus I'm pretty sure 30 meters will last me until the end of time.

Thanks to everyone who chimed in!

There's indeed more than one way to skin a cat, none of them particularly good for the cat. I've always wondered about that expression: was cat skinning a common thing back in the day?

Well, it's certainly vintage: etymology - Origin of the phrase, "There's more than one way to skin a cat." - English Language & Usage Stack Exchange

That is a fun website!

A little brass tubing (hobby stores) will do the paint protection.. but actually the cast BB will be fine for your lifetime -- with the tiny cable motion of shifting..
posting above was a few that are already a generation old, and still on the road..

with 300 bike shops in Portland, IDK why you cant find stuff ? call around on the Phone.

A WD-40 straw (or equivalent) works perfectly.

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.