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Bicycle Glossary - I


Imron - A brand of paint which is favored by custom frame builders and painters. Originally designed for trucks and cars, it is also good for bicycles. Imron is a two-part enamel paint made by DuPont. Two chemicals are mixed just before the paint is applied. Imron is highly toxic. A proper charcoal filter must be worn to protect the painter. Synonym: polyurethane enamel.

25-Ways: Professional Bicycle Painting

Inch - A dimensioning system originally applied to bicycles constructed in America and the British Empire, which is being fazed out. Interestingly, the standard became so strong that bicycles manufactured everywhere in the world still use it for some of their parts, such as chains and sprocket width (1/8-inch and 3/32-inch by 1/2-inch between links) There are exactly 25.4 millimeters in one inch. Inch is often abbreviated as in. See also: SAE.

Inches - An expression of the multiplication of speed at the rear wheel due to the sprocket(s) at the crank being larger than the sprocket(s) at the rear hub and the diameter of the rear wheel. Gearing is measured in "inches" like so: Number of teeth on front sprocket, divided by number of teeth on rear sprocket, times diameter of the rear wheel in inches. This is a nominal figure, because pi is not part of the formula. If you multiply the result by pi, then the number you get is the number of inches actually traveled for each revolution of the crank.  Synonym (sometimes): gearing.

Index shifting - Until about twenty years ago, shifting derailleurs was a skilled operation. There were no positions on the shifter - you moved the lever until the chain jumped onto the sprocket you wanted, then, if the chain was not aligned just right with the new sprocket, you jiggled the shifter a bit to get the chain to run smooth and quiet. Many bicycles still use this shifting system, referred to as "non-index shifting." Most new bicycles have detents or clicks in the shifting mechanism, and as you move the shifter into any click, the derailleur handles the rest of the chore of putting the chain where you want it automatically. 

Index shifting requires one more adjustment beyond what derailleur-equipped bikes without index shifting need. The cable tension must be adjusted so that the detents match the necessary positions of the derailleur. This is easier that it might seem. There is an adjusting barrel on the shifter or derailleur. The adjusting barrel is a long hollow bolt at which the cable housing stops, but the inner wire continues through. By unscrewing the adjusting barrel the cable becomes tighter. To adjust index shifting, try unscrewing the adjusting barrel a turn at a time and see how the bike shifts. If the shifting gets worse, turn the adjusting barrel the other way. 

Indicator chain - A small chain coming out of a hollow axle nut on Sturmey-Archer and Suntour three-speed, four-speed and five-speed wheels. This is attached to the control cable which leads to the shifter. The end of the indicator chain is a threaded rod with a locknut. You can adjust the shifting mechanism by tightening or loosening the connection of the cable to the indicator chain, the setting the locknut against the connection to keep it from drifting. There are two ways to adjust this type of shifting system:

1. Hold the shifter exactly between second and third gear positions. Adjust the cable tension until the pedals can turn forward without turning the wheel. This neutral position should be exactly between second and third gear. As you move the shifter toward second or third, the hub should securely engage the gear before the shifter is fully in position, so there is no chance of hitting neutral unexpectedly when shifting into second or third on the road. 

2. Look into the side of the axle nut where the indicator chain comes out, if the kind of axle nut has a sighting hole in it. When the shifter is in the second gear position, there is a shoulder on the rod to which the indicator chain is attached, which should be even with the end of the axle. This is why it is called an indicator chain. 

Indicator chain on the lower, Sturmey-Archer hub.  The upper Shimano hub is equipped with a bellcrank.

Inflation - The amount of compression of the air in a tire. Almost all bicycle wheels have an air-filled tire, generally with an inner tube which is like a balloon to seal in the air. The compressed air makes the ride more efficient and comfortable. The pressure is usually measured in pounds per square inch. The average modern fat tire takes a pressure of up to 65 pounds per square inch (PSI). The average thin tire takes up to 100 pounds per square inch. The exact recommended pressure varies from one model of tire to another, and is almost always molded into the side of the tire. In Europe, another system of air pressure measurement is sometimes used called "bars" which refers to multiples of standard barometric pressure (14 pounds per square inch) Synonym: Air pressure.

Inner tube - Because bicycle rims usually have holes in which spokes are mounted, it is difficult to seal them air tight. Therefore, unlike most "tubeless" car tires, bicycle tires use inner tubes as air seals. Even sew-up tires have inner tubes sewn inside. The inner tube has no structural strength, the tire is depended on for strength, but the inner tube is the bladder which actually contains the air. Synonym: Tube.

Inner wire - The braided or twisted series of strands making up the inner portion of a brake or derailleur control cable. See "Cable." 

Invisible kickstand - A technique in which a rider can come to a stop and maintain balance without taking any feet off the pedals. Synonym: Track stand - which see for more details.

Italian Standard - A old set of dimensions which were used to insure parts interchangeability among all manufactures following the Italian Standard.  For instance, pedals from a Bottecchia will fit cranks on a Mondia. Unlike American, English and French standards which use threads with a sixty degree angle, the Italian standard uses 55 degrees. See also Schwinn.

See also: Parts interchangeability chart


Anything missing or need greater coverage? Let me know - Jeff

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Although I have attempted to cover the major safety issues, I cannot be responsible for your use of this information. Working on bicycles is dangerous if you do it without considering consequences of bolts left loose, known problems which are ignored, things which should be replaced but are glued instead, and so on. Proceed carefully at your own risk and use common sense. Jeff Napier, and all agents associated with this information, do not offer any guarantee or warranty for your use of this information.

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