BICYCLE CABLE BASICS TUTORIAL
Figure 1 - A few universal bicycle cables
Bicycle cables transfer motion from your brake levers and shifters to the brake and shifting hardware with very little friction loss. Unlike rods, cables also allow forces to be “bent” around corners, so a bicycle can have all of the braking and shifting hardware attached to the handlebars, which are constantly moving. Without the cable’s ability to transfer motion around corners, all of the shifting and braking hardware would have to be installed on the frame, making it difficult or dangerous to operate. Cables are easy to install, adjust and maintain, and you will certainly be working with them when you create a new cycle, as it will normally require at least four cables for dual wheel braking and complete shifting.
A bicycle cable consists of two main parts: an inner cable that consists of several twisted strands of flexible hardened steel and an outer sheath that is made up of a hardened steel coil wrapped in protective rubber. Often, there will also be a lead ball formed at one or both ends of the cable that allows connection to a lever or shifter. Bicycle cable is very flexible to a point, and then the sheath will be bent or friction will impair the motion of the inner cable, so there are limits to how tight of a corner a cable can be bent around.
On mass manufactured cycles, the sheath is often omitted as much as possible, with the bare inner cable running along the underside of the frame tubing. The longer the sheath, the more losses that will occur due to sheath compression so the running of “open” inner cable is actually a good design. Figure 1 shows a typical hardware store “universal” bicycle cable that includes a formed head at each end. This is the type of bicycle cable you will most often use in home built creations, and it will need to be cut to a custom length.
Figure 2 - Cable ends often have a ferrule
Several bicycle cable sheaths are shown in Figure 2. The top two cables have an end cap (ferrule) that protects the end from damage and helps it seat into the hardware it mates with. When cutting your own cables, you will probably not have and end cap, but this is okay as long as you have trimmed the end properly using techniques that will be discussed later. The cable at the bottom of Figure 2 has been custom cut, so it has no end cap.
Figure 3 - Brake cable is larger than shifter cable
Braking cables have a larger diameter inner cable and head than shifter cables since they have to endure a much greater amount of tensile (pulling) force. The two center cables shown in Figure 3 are obviously larger than the outer two cables - they are brake cables. Also, notice how much larger the brake cable head is compared to the shifter cable head.
At the top of Figure 3 is shown a badly frayed cable, which is a serious stabbing hazard and will need to be cut in order to use the cable. The hard steel strands are like needles, and will easily punch through a light glove and into your skin, so be careful with frayed cable ends or newly cut cables. Sometimes you can simply twist the strands back together if they have unraveled, but once bent, you will have to cut the damaged part off.
Figure 4 - Cable is cut using large wire cutters
To cut a cable or its sheath, use a pair of electrician’s cutters (shown in Figure 4) or a large sharp wire cutter. Both the sheath and inner cable are made of very hard steel, so a typical set of small wire cutters will have no chance of cutting through. A zip disc in an angle grinder also works great for cutting cables, especially the sheath, which could end up with a piece sticking out after cutting with inadequate cutters.
Figure 5 - A frayed cable must be trimmed
The cable shown at the top of Figure 5 has been pinched by the brake hardware and then frayed at the end, so it needs to be cut at a point where there is no damage to be used. Every time you trim a cable, you must also trim the sheath, so expect to lose a few inches in the process. The image at the bottom of Figure 5 shows a properly cut inner cable after cutting just below the damage using the electrician’s cutters shown in Figure 4.
Figure 6 - A standard bicycle brake lever
Almost every type of bicycle brake and derailleur will require a cable and some type of lever to activate it. The lever pulls the braided steel cable through the outer housing, transferring energy to the brake system. Most levers can move the inner cable about 1 inch, which is plenty of distance to allow for light braking all the way up to a full wheel lockup.
A typical brake lever is shown in Figure 6, having a steel lever and a hard plastic body that can clamp to a handlebar. Notice the slot and opening that allow the round head to be inserted and locked into the lever. The same type of system is used on a shifting lever, although it has a smaller opening.
Figure 7 - The nut and bolt hold the cable
At the “business” end of the cable will be a derailleur or brake of some type. Since only one end of the cable has a formed head, the other end of the cable must be fastened by some type of clamping system that usually consists of a bolt with a hole through it so that the cable can be crushed onto the arm. Figure 7 shows a typical pad brake that grips the cable end using the bolt and nut method described. Front and rear derailleurs use the same type of system to grab the end of the cable.
Figure 8 - A cable noodle and end cap
Another brake is shown in Figure 8, which also includes a few other small cable trimmings that help make things work better. The small steel 90 degree corner is often called a “noodle”, and it allows for a friction free 90 degree bend at a very tight arc, something that cannot be done with the cable sheath. Also shown is a small cap that has been crimped to the end of the cable sticking out past the fastening bolt. This end cap stops the cable from fraying and protects hands from being stabbed by the sharp cable end. This end cap can be pulled off and reused on your own creations.
The SideWinder can fold almost right in half, making it a unique variable wheelbase bike that can turn around in about the space of a single sidewalk block. By shortening the wheelbase, the turning circle is drastically reduced, making the sidewinder seem as though it can spin in a circle or slither around a corner in ways that defy logic.
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