Why does cable routing utilize alternation of sections of shielded and unshielded cable?

Question

Why do manufacturers do this? What's even more interesting, many a bike have the middle cable fully housed, while the other two are "interrupted" as shown above.

IMHO those are the pros and cons of interrupting cable housing:

Advantages:

• lighter

Disadvantages:

• more complicated to cut to length and install
• more friction as there are a lot of enter/exit points for the cable into the housing
• far more susceptible to dirt and water
• more expensive, because of end caps and labor cost.

As is evident, in my opinion, all cables should have uninterrupted housing. However, all kinds of bikes in all price ranges have these intermissions - on the top tube, bottom tube, seatstay (for the RD). And it is not a factor of weight, as 10-year old massive steel frames also utilize it.

There must be an explanation. But what is it?

Answer 1

I believe one reason is more "stiffness" in the cable. Cable housing typically contracts when the cable is contracted. That's why Nokon also builds bicycle cable housing now. With The frame attachments, you get almost half a meter less housing that may contract. This could lead to crisper shift and brake feel.

Answer 2

1. It's not a given that the full-length housing is lower friction. I suspect that a well-done exposed cable scheme is lower friction than a full housing.
2. Especially for indexed shifters, the cable housing changes effective length with tension and temperature changes. The exposed cable scheme has much less flex and hence more precision shifting.
3. The full-length housing is ugly!

I haven't looked at new bikes much in about 5 years, but prior to that the full-length housing was almost exclusively seen on inexpensive bikes, while the exposed cable was common on the more expensive ones. This strongly suggests that cost is not a reason for exposed cables. (And reason also suggests this -- the housing is cheaper than the housing ends, eg.)

Of course, full-length housings are more compatible with suspension bikes, and probably have some advantages on true off-road bikes. So you'll see full-length housings more and more on bikes in that spectrum.

Answer 3

The installation is actually much easier for the interrupted housing. Keep in mind that the cable is housed for the bent sections, and unhoused for for the straight sections. In a bended section, housing will keep itself in place through tension, and pretty much any round shape will do the job. In a straight section, you'd have to bend the housing exactly straight, and fixate it to avoid bending under stress. It's much easier to just have the cable running straight under tension.

I don't think that there is much friction at the entry/exit points of the housing, and you have more points to apply lubrication.

Answer 4

I think you've got most of the reasons already. A couple of others:

Pros

• cheaper to manufacture (less outer meaning less metal, same amount of inner)
• lighter
• easier to route cables (no need to feed outer through tubes or bend it into twist holders - look at how hydraulic tubing is routed as a comparison point)
• less friction when clean and new (ie, in the bike shop when you're buying it)
• ease of servicing (releasing a cable is much easier as you can pop it out of a frame attachment rather than having to undo the end bolt)
• quieter (much less slapping against frame tubes)
• for the maker and seller, more frequent servicing, more frequent replacement (due to water getting in)

Cons

• for the owner, more frequent servicing and replacement

Note that almost no-one does entirely outer sheathed on derailleur geared bikes because the bend under the bottom bracket to the front derailleur is too awkward.

I suspect cost to manufacture is the main driver of this, with weight a secondary consideration. On cheap bikes, it will be purely cost. That's why I'm sure it's cheaper, because on cheap bikes there is almost nothing that could be done more cheaply. Suspension and other sale gimmicks are the exception, obviously, but I've never seen "exposed gear cables" advertised as a feature on a cheap bike.

Answer 5

I think bike manufacturers play on the looks of the bike with the split housing, making the bike look more advanced and professional and they actually charge more as well. Practically it makes much more sense to have the fully sleeved well lubricated cables, i.e. less water ingress/corrosion and dirt and easier maintenance.