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Bicycle chain

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This article is about the drive chain on a bicycle. Chain locks for bicycles are discussed in the Bicycle lock article.

A bicycle chain is a chain that transfers power from the pedals to the drive-wheel of a bicycle thus propelling it.

The chain in use on modern bicycles is a roller chain with a 1/2" pitch. Chain comes in either 5/32", 1/8", 3/32" or 3/16" roller widths. 5/32" is used on cargo bikes and trikes, 1/8" is used on the common low cost coaster (back pedal brake) bike, and on three speed, fixed gear and track bicycles, and 3/32" is used on derailleur-equipped road bicycles such as racing and touring models.

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.

Efficiency

A chain as used on a bicycle can be very efficient. Efficiencies of 98.6% have been measured Surprisingly, lubrication of the chain didn't effect 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". 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".

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.

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.

Sizing

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).

Manufacturers

Bicycle chains are made by companies such as:

See also

References

External links



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Last updated on Sunday March 09, 2008 at 14:27:53 PDT (GMT -0700)
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