Given that they control the shifting (
and often the braking as well) of your bike, cables and housing most certainly don't get the respect that they deserve. We often take it for granted that a shift cable will almost never fail during a ride, or that, barring wear and tear, its housing will assuredly never come apart. That feeling of security comes from many decades worth of manufacturing experience and has resulted in the relatively inexpensive cable becoming an unsung hero of the modern mountain bike. Jagwire's Tech Support Specialist Ben Oliver has been working with cables, hoses, and housing for the past fifteen years, including wrenching for professional cycling teams around the globe, and here he sheds some light on this often overlooked subject.
What exactly are a shift cables and housing made of?Shift cables are typically made using nineteen steel wire strands, either galvanized
or stainless. An inner core is created using seven strands with an additional twelve
wrapped around the outside in a slight spiral.
Shift housing features four layers. From the inner-most layers out, they include:
• a polymer inner liner, which may or may not be lubricated
• a shell made of linear steel strands
• another polymer layer that stabilizes the linear shell
• and an outer layer of housing that faces the elements
A dissected view of shift housing Is there really a difference between brake and shift housing?There is a critical difference in the inner shells of brake and shift housing. Brake
housing has a shell of coiled, flat wound wire wrapped around the inner liner. This
wound wire flexes slightly to resist the significantly higher load that brake cables put
on housing. This flexing would wreak havoc on shifting performance because it
doesn’t deliver the precision movement needed for clean shifts.
Shift housing resists this flexing by using linear strands of wire that run the length
of the housing parallel to the shift cable. These wires experience much lighter
loads, but are designed to keep the housing from compressing, resulting in clean,
crisp shifting. If you’ve ever tried to use shift housing in place of brake housing you’ve
seen what a poor substitute it is. The force of braking will either cause the linear
strands of wire to compress and bow out or simply split the housing into pieces.
All this, not to mention the cables and housings for each application are of vastly
different size, are reasons to never switch up the two.
And why is it that shift cables are made from spiral steel strands instead of a simpler straight wire?Cables today are made from spiral steel wires to deliver strength and durability, while still remaining flexible. A single or series of straight wires would be extremely stiff and vulnerable to breaking when curved.
We've all seen cables rust, but could this cause them to fail?Rust can obviously be a cause, but most frequently it’s general fatigue and wear. When overused or installed incorrectly, cables can fray due to movement against cables guides, tight bends in the frame or shifter, etc...
How is the cable "head" attached to the cable, and why is it the shape it is?The shape of the cable head is dictated by the individual OEM component manufacturers.
Mountain bike brake cables have settled on something fairly standard, whereas road
components have a couple different types of cable heads for both shift and brake.
The attachment of the cable head is accomplished by first cutting the cable, then spot
welding the end. Once complete, the welded end is “punched,” causing the individual
strands of the cable to mushroom out. This mushrooming allows the cable head to be
forged around and through the strands making it extremely strong and resistant to being
pulled off the cable during braking or shifting.
Shift cables are often used to control dropper seat posts as well. Mechanics often use the phrase "cable stretch." What does this mean, and is it all down to the cable or does housing play a part?In general, cables today are all pre-stretched. The “cable stretch” phenomenon has more
to do with housing compression that occurs after installing new cables.
If you’ve ever put on new brake cables and housing you know the way to finish everything
off is to give the lever several hard squeezes. This compresses the flat-wound wire and
“stretches” the housing. There’s a noticeable change in lever feel once this has been done.
It’s less of an issue with derailleur cables and housing, but it’s still good practice to get any
settling that the cables and housing are going to do out of the way before you send a new
bike out on its maiden voyage. This can be difficult if the bike uses internal cable routing. But
again, it’s usually not as dramatic on shift cables, and if it does occur all it takes is a simple
twist of a barrel adjuster to take up the slack.
www.jagwire.comFollow Mike Levy
@MikeLevyPB 
no need to lube (and looks cool ).
well outer cables, shit gets messy trying to lube the inners' just flush the outer through with some gt85/tf2 spray, but make sure to de-grease the outside of the outers, dont want dirt sticking anywhere near the entrances to cable outer. 
