MTB drivetrain check: Everything you need to know about shift cables & outer casings

Nothing is more annoying than a rattling chain. We often look for the fault in the adjustment of the rear derailleur or a bent derailleur hanger. However, the cause often lies deeper - more precisely: in the derailleur cables and outer casings. While we invest hundreds of euros in high-end drivetrains, the "central nervous system" of your bike - at least if you are still shifting mechanically - lives a shadowy existence.

Anatomy of a shift cable: steel meets high-tech

A switching system always consists of two partners:

1. The inner train: A braid of wafer-thin, twisted stainless steel wires (usually 1.1 to 1.2 mm in diameter). High-quality versions are ground (Ultraslick) or coated (PTFE/Teflon) to minimise friction.
2. The outer shell: It is far more than just a plastic tube. Inside, longitudinal wires (steel inserts) support the housing so that it does not buckle under tension - only then can it transmit the shifting commands to the rear derailleur reliably and without loss. A plastic liner (often made of Teflon) ensures that the inner cable glides in an almost floating manner.

The crucial question: to lay continuously or intermittently?

It used to be standard: the outer shell was interrupted at frame stops, the bare wire usually ran along the down tube.

1. The advantage: A few grams less weight and a little less friction when new.
2. The disadvantage: Dirt and water have free access at every interruption. If you still rely on an interrupted cable routing, you should definitely install the sealing tubes that manufacturers such as Shimano supply with their derailleur cable sets. We recommend sealed stop sleeves at the end stops (black sleeve with three grooves for Shimano).

Our recommendation: Lay trains end-to-end

Anyone who rides a lot off-road, in mud or in winter should Continuous laying set. The cover protects the cable from the gear lever to the rear derailleur. Modern frames are often designed for internal, continuous guides. If your frame has stops, you can often convert it to continuous with special adapters or by carefully drilling out (caution: loss of warranty!).

The alternative: There is also the option of fitting an additional plastic liner over the shift cable if the cable routing is interrupted. This also protects the shift cable over its entire length. This method used to be widespread - the Gore Ride On cables (no longer available) were the benchmark here. Today, manufacturers such as Jagwire offer sets with an additional liner - for example the Jagwire Elite Sealed Shift Kit.

Advantages and disadvantages of the outer shells at a glance

Service interval: When should I change the outer casing?

Do the trains or the covers wear out faster? As a rule it is the Outer shell. The inner cable "saws" into the plastic liner over time, especially in tight bends on the handlebars or rear derailleur.

1. Change check: We recommend replacing them once a season or every 5,000 km.
2. Warning signals: Shifting to larger sprockets requires a lot of manual force, or the chain only jumps to the smaller sprockets with a delay when shifting down (an indication of too much friction in the casing).

The professional workshop: What is important when switching

When you swap trains, the care you take will determine your performance over the next few months. Follow these three golden rules:

1. Clean cuts are everything: Never use side cutters! Use a special Bowden cable pliers. A crushed sleeve end massively increases friction. Expand the inner liner again after cutting with an awl or needle.
2. End cap check: Always use high-quality end caps. At exposed points (rear derailleur) Sealed end caps with a small rubber sleeve are worth their weight in gold. They prevent swirling dirt from travelling directly into the cover.
3. No fat voodoo: Modern liners are designed for dry running or factory-fitted silicone oil lubrication. Viscous grease attracts dirt and sticks in the cold. If at all, only use special, low-viscosity silicone oil.

How we test shift cables & outer casings

We used extensive measurements and a specially developed test bench to scrutinise shift cables from a wide range of manufacturers. A semi-automatic Bowden cable machine served as the test bench. A pneumatic cylinder is connected to a beam that moves up to 14 cables back and forth in parallel. The cables are deflected through 180 degrees in a wide and a narrow arc, with the cables or liners lying freely in between.

After a running-in phase (measurement one after 500 strokes), the test protocol provides for four load cycles: 1500 strokes dry (measurement two), 800 strokes wet with the addition of quartz sand (measurement three), a further 2000 strokes dry after a twelve-hour break (measurement four) and a further 800 strokes wet and under sand bombardment (measurement five). After each cycle, the friction was measured separately for each train.

We can recommend these outer covers

Our test provided the clear result that investing in branded cables is reflected in better shifting behaviour and longer durability. The derailleur cable sets from third-party suppliers such as XLC or Alligator only delivered mediocre performance. In our experience, the following products are particularly recommended:

• Jagwire Pro Shift Kit: After the running-in phase, the cables deliver very low friction. The restoring force is constantly high. The clip-on liners in particular contribute to good protection. They keep the system tight. The coated inner cables run extremely smoothly. Frame protectors complete the scope of delivery. Price: 35,99 Euro
• Shimano shifter cable set Road polymer-coated: The polymer-coated cables from Shimano are definitely worth an investment. The set comes with very good features. Each stop sleeve is fitted with a separate seal. Very low operating forces. Installation is a breeze. Price: 39,95 Euro
• Sram Slickwire: Who knows how long Sram will continue to offer shift cables. The Americans have been consistently focussing on electric drivetrains for years - but the Slickwire shift cables are still worth a recommendation. Sram does supply frame protectors, but there are no mudguards. The cables are quick to install, but the end caps are difficult to fit. Overall, however, the performance is at a high level. Price: 44 Euro

Shifter cables and outer casings - what the editors say

A set of high-quality covers and cables for the bicycle derailleur usually costs around 30 euros, but often does more than an expensive derailleur upgrade. Invest the time in clean shifting - shifting!

The differences in the cables are made by the seals: Well-sealed cables often run a little heavier when new, but are significantly more durable than unsealed ones. The smooth-running Jagwire cables for just under 36 euros work surprisingly well.

The shift cable sets from Shimano and SRAM are also good value for money. The durability can be extended even further with a continuous outer housing. Teflon-coated inner cables do not offer any measurable advantages.