Bicycle chain - WikiHQ

thumb|350px|Bicycle chains

thumb|Roller chain and sprocket

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 nickel-plated to prevent rust, or simply for aesthetics.

History

Obsolete chain designs previously used on bicycles included the block chain, the skip-link chain, and the Simpson lever chain. The first chains were of a simple, bushing-less design. These had inherent reliability problems and a bit more friction (and mechanical efficiency losses) than modern chains. With these limitations in mind, the Nevoigt brothers, of the German Diamant Bicycle Company, designed the roller chain in 1898, which uses bushings. More recently, the "bushingless roller chain" design has superseded the bushed chain. This design incorporates the bearing surface of the bushing into the inner side plate, with each plate creating half of the bushing. This reduces the number of parts needed to assemble the chain and reduces cost. The chain is also more flexible sideways, which is needed for modern derailleur gearing, because the chainline is not always straight in all gear selections.

The first solid bush-roller patent was filed by the Renold Chain company in 1880.

Early examples of chain-driven bicycles include the 1869 Guillemot and Meyer, the 1879 Lawson, the 1884 McCammon, the 1884 Starley Rover, and the 1895 Diamant. The study, performed in a clean laboratory environment, found that efficiency was not greatly affected by the state of lubrication.

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 cyclist's leg free from oil and dirt.

Lubrication

thumb|right|Bicycle chain laying in melted pure paraffin wax without additives. The sticky film indicates that the wax is about to solidify, and that the chain should be taken out.

How best to lubricate a bicycle chain is a commonly debated question among cyclists.

Wet lube

Liquid lubricants, like oil, penetrate to the inside of the links and are not easily displaced, but quickly attract dirt. The outside of the chain should be wiped dry after the wet lubricant has had enough time to penetrate into the links to avoid pickup of dirt.

Dry lube

"Dry" lubricants, often containing wax or Teflon, are transported by an evaporating solvent, and stay cleaner in use, but are less durable, and require frequent maintenance.) instead of oil based lubrication. Immersion wax stays cleaner in use and is reasonably durable, but requires an initial thorough degreasing (for example using white spirit followed with isopropanol) before the first wax immersion, and some basic equipment to melt the wax and re-wax when needed. Re-waxing may be necessary every 200-400 kilometers depending on riding conditions (dusty, wet or muddy conditions may require more frequent re-waxing). One popular method is to put the cleaned chain in a bowl and melt the wax in a water bath as a safety measure instead of melting directly in a pan, to minimize fumes and avoid overheating the wax which can be a fire hazard. Alternatively, chain wax melting equipment which fulfills the same purpose can be purchased. Since the waxing requires a little setup each time, many cyclists wax two or three chains at a time, and rotate between them one by one as the wax wears off. Long-distance bicycle tourists may even carry a spare chain that has been waxed. Drip-wax may also be an alternative for lubrication in the field as the wax wears off.

Chain removal

thumb|Chain tool

On most upright bicycles, the chain loops through the right rear triangle made by the right chain stay and seat tube. Thus a chain must be separated, (or "broken" ) unless the triangle can be split (usually the seat stay). Chain can either be broken with a chain tool or at a master link. A master link, also known as a connecting link, allows the chain to be inserted or removed with simpler tools, or even no tools, for cleaning or replacement.

Wear

thumb|right|Four lengths of bicycle chain with the same number of links but with different degrees of wear. They show chain stretch, a consequence of wear|upright

thumb|right|A chain-wear tool that exactly measures the length of a given number of chain links to detect when a chain is excessively worn; the two sides of the tool measure different degrees of wear

Chain wear, often misleadingly called chain stretch, becomes an issue with extensive cycling. The wear is removal of material from the bushings and pins (or half-bushings, in the Sedis design, also, called "bushing-less", where the bushing is part of the inner plate) rather than elongation of the sideplates. The tension created by pedaling is insufficient to cause the latter. Because the spacing from link to link on a worn chain is longer than the specification, those links will not precisely fit the spaces between teeth on the sprockets. This can result in increased wear on the sprockets, and possibly "chain skip" on derailleur drivetrains, in which pedalling tension causes the chain to slide up over the tops of the sprocket teeth and move ("skip") to the next alignment, reducing power transfer and making pedalling uncomfortable.

Since chain wear is strongly aggravated by dirt getting into the links, the lifetime of a chain depends mostly on how well it is cleaned and lubricated, and does not depend on the mechanical load.

Nickel-plated chain also confers a measure of self-lubrication to its moving parts as nickel is a relatively non-galling metal.

Chain wear rates are highly variable. One way to measure wear is with a ruler or machinist's rule. Another is with a chain wear tool, which typically has a "tooth" of about the same size found on a sprocket. They are placed on a chain under light load, and if the tooth drops in all the way, the chain should be replaced.

Twenty half-links in a new chain measure , and replacement is recommended before the old chain measures (0.7% wear). to 1980—called Shimano Dura-Ace 10 pitch. The Shimano 10 pitch system is incompatible with ANSI standard #40 (1/2″) e.g. chains, sprockets and so on, and was outlawed by the Japan Keirin Association, helping in its demise. (Fixed sprockets and freewheels are also available in widths, so fixed-gear and single-speed bikes can be set up to use the narrower and lighter chains.)

chains are typically used on bikes with a single rear sprocket: those with coaster brakes, hub gears, fixed gears such as track bicycles, or BMX bikes.
chains are used on cargo bikes and tricycles.

With derailleur-equipped bicycles, the external width of the chain (measured at the connecting rivet) also matters, because chains must not be too wide for the cogset or the chain will rub on the next larger sprocket, and chains must not be too narrow, which allows them to fall between two sprockets.

Chains can also be identified by the number of rear sprockets they can support, anywhere from 3 to 13. The following list enables measuring a chain of unknown origin to determine its suitability.

6 speed – 7.3 mm (9⁄32 in) (Shimano HG), 7.1 mm (9⁄32 in) (SRAM, Shimano IG)
7 speed – (Shimano HG), (SRAM, Shimano IG)
8 speed – (Shimano HG), (SRAM, Shimano IG)
9 speed – (all brands)
10 speed – (Shimano, Campagnolo)
10 speed (narrow) – (Campagnolo, KMC)
10 speed (narrow, direction) – (Shimano CN-5700, CN-6700, CN-7900)
11 speed – (Campagnolo, KMC, Shimano CN-9000)
12 speed – (SRAM)
13 speed – 4.9 mm wide – Campagnolo Ekar

The Wikibook, "Bicycle Maintenance and Repair", has more details on this topic.

Chain 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 onto the largest front chain ring and the largest rear sprocket without jamming, and not so long that, when shifted onto the smallest front chain ring and the smallest rear sprocket, the rear derailleur cannot take up all the slack. Meeting both these requirements is only possible if the rear derailleur is compatible with the gear range being used on the bike. It is broadly accepted as inadvisable to actually use the large/large and small/small gear combinations, a practice known as cross-chaining, due to chain stress and wear.

In the case of single-speed bicycles 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 sprocket. 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.

Variations

In order to reduce weight, chains have been manufactured with hollow pins and with cut-outs in the links. Chains have also been made of stainless steel for corrosion resistance and titanium for weight reduction, but they are expensive. A recent trend is chains of various colors, and at least one manufacturer offers a chain model specifically for electric bicycles.

Manufacturers

Notable bicycle chain manufacturers include:

Renold
Campagnolo
Rohloff AG
KMC Chain
Shimano
SRAM
Wippermann

References

External links

Wikibooks Bicycle Maintenance and Repair – see the section on Chains
Animation of Shimano gearing system

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