Bicycle chain
From Wikipedia, the free encyclopedia
A bicycle chain is a roller chain that transfers power from the pedals to the drive-wheel of a bicycle thus propelling it. Most bicycle chains are made from plain carbon or alloy steel, but some are chrome plated or stainless steel to prevent rust or simply for aesthetics.
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[edit] History
Obsolete chain designs previously used on bicycles included the block chain, the skip-link chain, and the Simpson lever chain. Virtually all modern chains are of the "Sedis" bushingless design, which is cheaper to make, promotes better lubricant flow inside the rollers, and has created more lateral flexibility for multi-geared bicycles.
Before the safety bicycle, bicycles did not have chains and the pedals were attached directly to the drive-wheel, thus limiting top speed by the diameter of the wheel and resulting in very dangerous designs with front wheels as large as possible. Using chain drive allowed the mechanical advantage between the drive and driven sprockets to determine the maximum speed, thereby enabling manufacturers to reduce the size of the driving wheel for safety. It also allowed for the development of variable gearing, allowing cyclists to adjust their gearing to the difficulty of the terrain, on the fly.
[edit] Efficiency
A chain as used on a bicycle can be very efficient. Efficiencies of 98.6% have been measured[1] Surprisingly, lubrication of the chain didn't affect efficiency of the chain much; "The role of the lubricant, as far as we can tell, is to take up space so that dirt doesn't get into the chain".[1] A larger sprocket will give a more efficient drive (reduces the movement angle of the links). Surprisingly, higher chain tension was found to be more efficient; "This is actually not in the direction you'd expect, based simply on friction".[1]
[edit] Maintenance
Chain lubrication is a common problem for cyclists. Liquid lubricants penetrate to the inside of the links and are not easily displaced, but quickly attract dirt. "Dry" lubricants, often containing wax or Teflon, have poor penetrating qualities unless carried in an evaporating solvent, but stay cleaner in use. The cardinal rule for long chain life is never to lubricate a dirty chain, as this washes abrasive particles into the rollers. Chains should be cleaned before lubrication. The chain should be wiped dry after the lubricant has had enough time to penetrate the links. An alternative approach is to change the (relatively cheap) chain very frequently; then proper care is less important. Some utility bicycles have fully-enclosing chain guards which virtually eliminate chain wear and maintenance. On recumbent bicycles the chain is often run through tubes to prevent it from picking up dirt, and to keep the cyclists leg free from grease and dirt.
[edit] Removal
On most upright bicycles, the chain loops through the right rear triangle made by the right chain stay, right seat stay, and seat tube. Thus a chain must be "broken" with a chain tool or at a master link (also known as a connecting link), which typically has one pin held by a C clip, allowing it to be inserted or removed with simple tools, to be removed for cleaning or replacement.
[edit] Wear
Chain wear, or chain stretch, becomes an issue with extensive cycling. Although the overall effect is often called "stretch", chains generally wear through attrition of the bushings (or half-bushings, in the Sedis design) and not by elongation of the sideplates. The tension created by pedaling is insufficient to cause the latter. Because an old chain is longer than needed, its links will not precisely fit the spaces between teeth in the drivetrain, making gear shifts a problem and possibly resulting in a 'skipping' chain that reduces power transfer and makes pedalling very uncomfortable.
Twenty half-links in a new chain measure 10" (254 mm), and replacement is recommended before the old chain measures 256 mm (0.7% wear). A safer time to replace a chain is when 24 half-links in the old chain measure 121/16 inches (0.4% wear). If the chain has worn beyond this limit, the rear sprockets are also likely to wear, in extreme cases followed by the front chainrings. Replacing worn sprocket cassettes and chainrings after missing the chain replacement window is much more expensive.
[edit] Sizes
The chain in use on modern bicycles has a 1/2" pitch, which is ANSI standard #40, where the 4 indicates the pitch of the chain in eighths of an inch, and metric #8, where the 8 indicates the pitch in sixteenths of an inch.
[edit] Width
Chain comes in either 3/32", 1/8", 5/32" or 3/16" roller widths: 5/32" is used on cargo bikes and trikes, 1/8" with the common low cost coaster (back pedal brake) bike, hub and fixed gearing and on track bicycles, and 3/32" with the derailleur gears most commonly fitted on racing, touring and mountain bikes.
The Wikibook "Bicycle Maintenance and Repair" explains that the difference between derailleur chains commonly labelled 8-speed, 9-speed, and 10-speed is in its external width (all are 3/32" chains).
[edit] Length
New chains usually come in a stock length, long enough for most upright bike applications. The appropriate number of links must be removed before installation in order for the drive train to function properly. The pin connecting links can be pushed out with a chain tool to shorten, and additional links may be added to lengthen.
In the case of derailleur gears the chain is usually long enough so that it can be shifted into the biggest front chain ring and the biggest rear cog without jamming, and not so long that, when shifted into the smallest front chain ring and the smallest rear cog, the rear derailleur cannot take up all the slack. Meeting both these requirements is not always possible.
In the case of single-speed bicycle and hub gears, the chain length must match the distance between crank and rear hub and the sizes of the front chain ring and rear cog. These bikes usually have some mechanism for small adjustments such as horizontal dropouts, track ends, or an eccentric mechanism in the rear hub or the bottom bracket. In extreme cases, a chain half-link may be necessary.
[edit] Variations
In order to reduce weight, chains have been manufactured with hollow pins and with cut-outs in the links.
[edit] Manufacturers
Bicycle chains are made by companies such as:
[edit] See also
[edit] References
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[edit] External links
- Bicycle chain length calculator and stretch/wear test
- Wikibooks Bicycle Maintenance and Repair - see the section on Chains
- The Complete Guide to Chain - general, not specific to bicycles
- How to calculate chain length (video tutorial)
