Check bike cables by looking for fraying, rust, kinks and stiff movement, and replace any that show them. Brake cables come first because their failure is the dangerous one. There is no verified mileage or month interval that fits every bike, so inspect on a routine (the pre-ride checklist is a good place for it) and replace by condition.
How cables work, and why they fail
A bicycle cable has two parts. The inner wire is made of twisted steel strands, and the outer housing is flexible steel, usually wound in a helix. The housing gives the pull of the inner wire something to push against: there cannot be a pull on an inner cable without an equal push on the housing. Modern housing also has a plastic liner around the inner wire, which considerably reduces friction.
Cables rarely wear out in the usual sense. They fatigue from repeated bending, and they usually break at the lever or where they pass over a pulley, usually with no symptom beforehand. Rust and seizing are separate problems, and both call for replacement. Bent helical housing can also stay lengthened, which causes spongy braking or imprecise shifting.
A shift-cable failure usually does not lead to a crash, but a brake-cable failure very easily can. That is why brake cables get the strictest inspection.
What to look for
- Fraying strands at the lever, at the cable ends or where the cable passes over a pulley.
- Rust on the inner wire, or a cable that feels gritty or sticky when you move it.
- Housing that is kinked, cracked or permanently bent, or with missing ferrules.
- Spongy brake feel or sluggish shifting that adjustment does not cure. Most brake and gear problems come from cable friction or misadjustment, so fix the cable before blaming the shifter or derailleur. For shifting faults, see why your bike shifts badly.
Choosing the right housing
| Type | Use | Note |
|---|---|---|
| Conventional helical housing | Brakes; shifting where the cable barely changes curvature | Cannot be compressed, but can lengthen if bent |
| Index-compatible housing | Shifting only | Relies on plastic to hold together; never use it for brakes |
Index-compatible housing should never be used for brakes. The loads on a brake cable can make it rupture and burst, causing a complete and sudden loss of brake function. Brake inner wire is also thicker than shift wire because it must resist higher tension, so do not swap one for the other.
Lubrication: less than you might expect
With plastic-lined housing, grease is the wrong choice: it makes cable movement sluggish. Many manufacturers recommend against lubricating cables at all, and sealed systems such as Gore-Tex cables should not be lubricated. On bikes ridden in wet conditions, a little oil can help, more as rust prevention than as lubrication. Follow your cable maker’s instructions where they exist.
Replacing a cable
If you are not confident, have a shop do brake cables. If you do the job yourself, do the following.
- Cut housing cleanly. Poorly cut or unshaped housing ends are a very common source of friction and sponginess. Helical housing can have its last loop crushed by the cut; a second cut can trim off the bent half-loop. Index-compatible housing is very difficult to cut without the proper tools, so use cutters made for it.
- Fit a ferrule on each end of cut housing whenever possible. Ferrules help keep the housing aligned with the cable stop it fits into.
- Thread and clamp the cable. For a derailleur cable, start with the shifter and derailleur in the slack position, usually the smallest sprocket. Before connecting, screw the adjusting barrel in fully, then back it out about a turn to a turn and a half so you can tighten or loosen later. Limit stops should not normally need changing after a cable swap, but the indexing will.
- Tighten the clamp bolt as specified. Anchor-bolt threads should be lubricated so they do not strip, and the bolts are small enough to strip or break. Use the torque value printed on the component or in the manufacturer’s instructions rather than a guess.
- Trim and cap the end. Leave the tail long at first, then trim it once everything works. An end cap stops unraveling, and it must be replaced with a new one every time the cable is disassembled and reassembled. Keep the tail clear of the chain and rings.
Test before you ride
Brake-cable anchor bolts are the most important fasteners on a bicycle. If they are not tight enough, the brakes appear to work in normal use, then in a panic stop the cable slips and the brakes fail completely, with no warning. To check, grab each brake lever in turn with both hands and squeeze hard. For shift cables, shift to the position with the cable tightest and pull hard on the lever.
Then, before riding in traffic, wheel the bike and apply each brake at walking pace in a safe, empty spot. Both levers should stop the wheel firmly without reaching the handlebar. If the lever pulls close to the bar, the cable slips, a strand is frayed, or the brake drags or rubs, stop and adjust or take the bike to a mechanic. The same applies if you are unsure about any step on a brake. See servicing your own brakes for pad and caliper checks.
E-bikes, hydraulic brakes and electronic shifting
Hydraulic brake lines are frictionless, offering smoother modulation of braking force, and they use fluid rather than cables. Electronic shifting needs no shift cables. The trade-off is that hydraulics and electronics are usually not repairable during a ride, whereas cable systems have no battery to run down. Bleeding hydraulic brakes and any work on a battery or motor wiring is a job for a qualified mechanic using the fluid and procedure your brake maker specifies. Cable-operated brakes and shifters on e-bikes follow the same rules as above. Wash gently, as covered in how to wash your bike properly, so water is not driven into cable ends.
Sources
- Sheldon Brown (Harris Cyclery): Cables
- Sheldon Brown (Harris Cyclery): Bicycle Cable Installation and Maintenance
Last reviewed: October 2026.