Smooth, not barbed, fence wire threaded through the original housing works as a stiff but functional brake cable, thinner wire works for shift cables, and small steel or copper tubing or tightly wound wire can stand in for housing. Check the stress first: a panic squeeze that puts 1,080 N in the cable loads a 1.6 mm wire to about 537 MPa, which soft wire cannot carry, and 50-lb fishing line breaks at only 222 N, so use the thickest wire the housing accepts and never fishing line on a brake.
Part of Bicycle Repair & Fabrication
Cable and brake substitutes are the wire, line and tubing used in place of manufactured control cables and housing on a bicycle.
How Much Pull Must The Wire Carry?
The brake lever multiplies the squeeze of the hand. Take an assumed lever ratio of 3.6 (hand end 90 mm, cable 25 mm from the pivot, as in Brake Adjustment):
- Normal squeeze, 100 N → cable tension 100 × 3.6 = 360 N
- Panic squeeze, 300 N → cable tension 300 × 3.6 = 1,080 N
Stress is tension divided by cross-section area (π d² / 4). At the panic load of 1,080 N:
| Wire diameter | Area | Stress at 1,080 N |
|---|---|---|
| 1.6 mm | 2.01 mm² | 537 MPa |
| 2.0 mm | 3.14 mm² | 344 MPa |
| 2.5 mm | 4.91 mm² | 220 MPa |
Soft, low-carbon galvanised fence wire yields at very roughly 250-350 MPa, while hard high-tensile wire carries several times as much (recalled handbook ranges, not measured here). So a 1.6 mm soft wire stretches or breaks in a hard stop, a 2.5 mm one sits just below that range, and the difference between soft and hard wire matters. A wire that bends easily by hand is soft. At the normal squeeze the 2.5 mm wire sees 360 / 4.91 = 73 MPa, which is comfortable.
Use the thickest wire that slides freely in the housing, and if it is soft, expect it to stretch with use and need the brake re-adjusted often (Brake Adjustment shows how 2 mm of cable stretch becomes about 7 mm of lever travel).
Fishing Line
Fishing line is rated by its breaking load: nominal 50-lb line breaks at about 50 × 4.45 = 222 N, and 100-lb braided line at about 445 N (recalled ratings; 1 lb of force is 4.45 N). Both are well below the 1,080 N panic load, and monofilament stretches and abrades. Fishing line is not a brake cable. It might be considered for very light work such as a derailleur return, and even there it will stretch.
The Housing
The housing is a flexible sheath that the cable slides inside, resisting the cable tension in compression so that the cable pull reaches the brake. The carrier’s substitutes are small-diameter steel or copper tubing, or tightly wound wire. Tubing is stiff and does not bend round the handlebar without kinking, so use it for straight runs and keep the bends gentle and few. A coil of wound wire compresses slightly under load, which adds lost motion at the lever. Grease the inside to cut friction.
What You Need
- Smooth fence wire, not barbed, in the largest diameter that fits the housing
- Housing: the original, or tubing or wound wire
- Pliers and wire cutters, and a file for the cut ends
- Grease
- A clamp bolt on the brake to hold the wire
Method: Fit And Test A Wire Cable
Step 1: Measure the housing bore and pick the thickest wire that slides freely through it.
Step 2: Check whether it is soft or hard by bending a short length by hand.
Step 3: Cut to length and dress the ends with a file, so no strand catches.
Step 4: Grease and thread the wire through the housing and the brake.
Step 5: Clamp it under the anchor bolt; leave a short tail, and bend the tail over so it cannot pull through or catch a finger.
Step 6: Set the brake as in Brake Adjustment.
Step 7: Test hard. With the wheel held, squeeze the lever harder than you ever would in use, and look for slip at the clamp, wire stretch and housing kinks.
Step 8: Re-check after the first ride and after every ride until you replace it with a proper cable.
Common Mistakes
- Barbed wire — it cannot slide in housing and tears it.
- Wire too thin — see the stress table.
- A kinked bend in the housing — the wire jams or snaps at the kink.
- Relying on one improvised brake with no backup — keep the other brake original if you can.
Safety
A brake cable that fails
A wire that snaps or pulls out of the clamp leaves the brake dead, usually at the moment of hardest braking. Ride slowly on an improvised cable, keep the other brake in proper order, inspect the wire for frays and kinks every ride, and replace it at the first opportunity. See Improvised Parts & Fabrication.
What’s Next
- Learn next: Frame Repair — the other structural repair
- Combine with: Iron Wire — making wire when none can be found