Please keep in mind that this question is specific to mountain bikes which roll through lots of dirt and mud. I heard stories of bikes that had their cable housing last for years, but I doubt that this applies to mountain bikes (or maybe it does).
How would I know when the housing needs to be replaced? Several options occur to me:
- As a rule of thumb, always replace the housing together with the cable. The reasoning is probably mostly the low cost of materials which is a few dollars.
To the other extreme, do not replace the housing unless you get some indication that it needs replacement. For example, visual inspection finds some wear and tear or the cable won't move freely while tugging it.
My current practice is to follow option 1 but I would be interested in knowing if there is perhaps a more efficient option backed by the experience of the masses.