Bicycles/Maintenance and Repair/Glossary

A

Actuation Ratio

In general, the change of input action divided by the change of output effect. In bicycles, it is most mentioned in relation to the indexed shifting of derailleurs, where it refers to the change in length of the shift cable divided by the transverse change in position of the derailleur across the cogs. Although the handlebar shifter no doubt has an actuation ratio of its own, it is the length of cable shifted that is of interest to indexed shifting. The reciprocal of actuation ratio is called the shift ratio, and this ratio is used more often. Typical figures for derailleur shift ratio are 1.7 for Shimano, 1.1 for the native SRAM set, and 1.5 for Campagnolo. In addition, SRAM makes a family of Shimano compatible shifter products with the appropriate cable shifts.

B

'B-height' adjustment

One of the three main derailleur adjustments. It sets the distance of the guide pulley below the largest cog. It is important for clean shifting and low cog / chain wear.

Barrel-adjuster

A screw adjustment that is installed in-line with brake or shift housings to simulate a change in the housings length. This causes a movement of the cable within the housing. Cable with housing is referred to as a Bowden cable.

Bowden cable

The combination of a steel cable in a reinforced flexible housing that is used to operate brakes and derailleurs.

Brake

The assembly on the wheel that brings the bicycle to a halt. It applies friction to a part of the wheel, for example the wheel rim or within the hub. Most bicycles have a brake on each wheel.

Brake arms

The parts of a brake assembly near the wheel the that pivot and provide any necessary leverage to assist in the application of the brake pads.

Brake balancing

The process whereby both brake pads are caused to reach the wheel rim at the same time. This ensures stability in braking.

Brake cable

The steel wire cable that connects a brake lever to the brake arms, used to operate the brakes. A part of a Bowden cable.

Brake housing

The reinforced, flexible cable conduit used by the brake cable. A part of a Bowden cable.

Brake lever

The lever on the handlebars operated by the rider to make a brake work.

Brake pads

The parts, usually rubber or leather, that come into contact with both sides of a wheel's rim to brake it.

C

Cable

A twisted steel wire that is used to operate brakes and derailleurs. Diameters vary between about 1.2mm and 1.5mm.

Cable cap

A small metal piece that fits onto the end of a cut cable to prevent its fraying. It is either crimped or soldered.

Cable clamp

Screwed fastenings at brakes and derailleurs used to fix cable ends.

Cable cutters

Special cutters that can cut tough steel cable. They are also used to cut reinforced cable housings. Both blades have v-shaped cutouts to avoid crushing the housing's end.

Cable housing

The outer part of a Bowden cable that acts as a conduit for the steel inner wire. It is supplied in both 4 and 5mm external diameters.

Cable sleeve

The lubricated cable route within the outer housing of a Bowden cable.

Cable terminal

The thickened end part of a cable that is designed to fit into shifters or brake levers, and acts as an anchor there. There are barrel-ends for the brakes of bikes with non-drop handlebars, pear-ends for racers, and button-ends for shifters.

D

Derailleur

The assembly near a wheel that moves the chain from one cog to another in order to change the ease of pedalling. It does so when the rider operates a shifter on the handlebars. Derailleurs exist for both the rear cogs and for the front chainrings, so increasing the number of gear combinations.

Derailleur capacity

The extent to which the chain can be made to tighten when a gear is selected that uses smaller cogs. The most severe test of a derailleur's capacity (total capacity) occurs when there is a shift from using the largest cogs on front and back, to using the smallest cogs on front and back. Total capacity is therefore expressed as the front chainring range plus the rear cog range (measured in teeth) , and decides a derailleur's suitability for given gear-sets. Derailleurs are made in so-called low, medium, and long-cage families for small, medium, and large total capacities respectively.

Derailleur hanger

A sacrificial metal plate that is fixed between the bicycle frame and the derailleur, designed to bend on impact instead of the other equipment. These differ greatly between bikes, and generally speaking are hardly ever interchangeable. Each has a lip whose angle sets the upper limit of the derailleur's 'B-height' adjustment.

F

Ferrule

A metal or plastic cap that is used on both ends of a Bowden cable's housing, to ensure alignment of the internal sleeve and to provide a good bearing surface. The inner cable extends through the ferrule while the housing's end is sealed. They are most often pressed on as a tight fit, but some are crimped onto housings. They are supplied with internal diameters of either 4 or 5mm. Ferrules come into contact with cable stops on frames or make a loose fit in the ends of barrel adjusters, and sometimes the ferrules for these purposes differ. Sometimes housing ferrules also have curved metal transitions, to better guide an inner cable at the brakes.

G

Gear-inches

A measure of the difficulty in pedalling. It is a calculated figure based on the two cogs in use at the time, and the diameter of the driven wheel. It is just the ratio of the front chainring and the rear cog (in teeth), times the diameter of the driven wheel (in inches). The gear-inch figures are used to plan gearing for the various riders' needs, and the road distance traveled with one complete turn of the pedals can be found by multiplying the gear-inch figures by the constant pi (3.142).

S

Shift Ratio

(See Actuation Ratio also). The reciprocal of actuation ratio. Shift ratio in bicycles most often applies to a property of derailleurs and is the inter-cog spacing of the cogset divided by the length of cable pull to make a shift.