Table of Contents
- Chain Drive
- Material & Manufacturing
- Bushed and Bushingless Chains
- Master Links
- Checking for Chain Wear
Bicycle drive trains are chain drives with roller chains. Chain drives were used in industrial machines for decades before they were adopted by the bike industry late in the 19th century. The manufacturing of roller chains, bicycles and lubricants was based on trial and error, experimentation and the concepts and models used by artisans and engineers.
The chain drive is made of links connected in a continuous loop. The links overlap, alternating as inner and outer. The links are made of plates; the plates are held together with rivets called pins. Hollow pins made of tubular steel are common. The pins are riveted to the outer plates. The pins connect the links to adjacent links; the links pivot on the pins.
A metal roller chain does not stretch. It wears, which makes it get longer – a longer chain fails to fit the cogs and fails. Microscopic wear on individual links adds up. With modern 11 and 12 speed chains, elongation of .5% (half of one percent) of the length of the chain leads to replacement. Some count 1 link as a set of 1 inner half-link and 1 outer half-link; others count all links. Pitch is the length of any link, outer or inner. Pitch (length) is the distance between pins, measured from the centers of pins. It can be expressed as an ANSI number, or a fraction of an inch, or in millimeters. See:
- Wikipedia, Bicycle Chain: Sizes;
- Wikipedia, Roller Chain: Chain Standards;
- Bicycle Technical Information, Glossary, Chain/Sprocket pitch;
- Bike Gremlin, Bicycle Drive Chain Standard Dimensions.
The standard pitch for modern bicycle chains is ANSI 40 (designating 4/8 inch) = 1/2 inch = 12.7 mm. On the all-links-are-counted assumption, a chain will normally be more than 100 links long. A road chain may have 108 links or more. A gravel or mountain bike chain will be longer. A chain for a compact road crankset with a 46 tooth large ring and a cassette with a 36 tooth large cog will be about 112 or 114 links long. Chain lengtt depends on the length of the chain stays and the diameters of the largest chain rings and cogs. Resources on measuring a chain:
- BTI (Sheldon Brown site): (Rear) Derailer Adjustment; Chain Length;
- (YouTube video) Alex Ramon at BikeRide.com, 2019, How to Calculate chain length;
- YouTube video, Global Cycling Network channel, 2016, How To Calculate The Correct Chain Length (Road Bike)
- YouTube video, Park Tool channel, How to Size a Bicycle Chain.
The BTI method of sizing a chain is to break a chain (remove links with a chainbreaker tool) to fit the largest rings. A chainbreaker pushes rivetted pins out. Another key measurement considers how the chain is tensioned when the chain is on the smallest rings. This makes sure the chain does not fold and rub on itself.
A 108 link chain is 1371.6 mm long; elongation by .5% is a fraction more than 6.8 mm. The Park Tool CC-3.3 drop-in chain checker gauge measures about 170 mm. to indicate if the elongation in a span exceeds .5%. In a span of 1/8 of the length of chain the gauge has to detect the difference between to a tolerance of .5 mm.
A roller chain has a few dozen open plain bearings which need lubrication, according to the opinions of builders, engineer and mechanics. Lubrication reduces the co-efficients of friction when steel surfaces in contact with each other. It can reduce wear if lubrication is applied often enough.
Lubrication is required for correct operation of mechanical systems such as pistons, pumps, cams, bearings, turbines, gears, roller chains, cutting tools etc. where without lubrication the pressure between the surfaces in close proximity would generate enough heat for rapid surface damage … .Wikipedia on Lubrication
… many chains … have to operate in dirty conditions, and for size or operational reasons cannot be sealed. Examples include chains on farm equipment, bicycles, and chain saws. These chains will necessarily have relatively high rates of wear, particularly when the operators are prepared to accept more friction, less efficiency, more noise and more frequent replacement as they neglect lubrication and adjustment.
Many oil-based lubricants attract dirt and other particles, eventually forming an abrasive paste that will compound wear on chains. …Wikipedia on Roller chain, July 2021
Material & Manufacturing
Chain link plates are punched out of steel sheet metal; usually carbon steel. Steels are alloys of iron and other elements. Carbon steel is more susceptible to oxidation (rust), corrosion and wear than other steels. Other steel would cost more and would require retooling by the chain manufacturers. On some chains link plates and other chain parts are plated with metal less suscepible to corrosion, or case hardened.
Adam Kerin of Zero Friction cycling provides an overview of materials at pp. 9-11 in his chain longevity testing brief:
The most common hardness ratings are Rockwell D and Vickers.
… the Vickers hardness test is generally regarded as the most suitable. Mild steel/stainless steel will typically have a Vickers hardness rating of around 150 to 200. Quality hardened steel will be 200 to 400, or even 500, and the highest level tool steels / high speed steels can be up to 700.
However – the harder you make steel, the less ductile and more brittle it becomes. Steel can be made with very high “toughness” – combination of hardness and ductility – but this is very expensive requiring alloying with multiple other metals plus quite exacting heating/cooling cycles. For bicycle chains … different manufacturers use a different level or grade of steel. Campagnolo for instance claim their chains are made of “special steel”. Exactly what grade of steel is used I am unlikely to every find out from manufacturers. But in summary for bicycle chains, you can expect the steel will be hardened for wear longevity but there is limit as to how hard they can make this steel without the chain becoming too brittle and snapping on the first poor shift – especially the more economical grade of steel that is used.Adam Kerin, Zero Friction Cycling site, Chain longevity testing brief, 2018
Bicycle manufacturers acquire chains from specialty manufacturers including Renold, Campagnolo, Rohloff, Wipperman, Shimano, YBN, KMC, SRAM and others. They make chains out of the same raw stocks, but have different machinery and workforces. Some chain manufacturers subcontract to each other. Bike chain manufacturing in 2022 is largely an Asian industry. A few chains are made in Europe and the US. (The packaging of US firm SRAM chains indicates those chains originate in Portugal). Some chains are still manufactured by German, French, English and Italian firms. A few chains are made in Japan. Many are made in Taiwan, the People’s Republic of China and other Asian countries with steel and heavy industrial supplies and capabilties. The steel in chains machined in Asia will normally have been sourced from Asian foundries – it will have been smelted and forged from iron ore and carbon, rather than from recycled steel. Pins are steel too. The pins are fabricated from steel stock according to the methods used by manufacturers. The steel mills decide how to forge, roll and process the steel. The chain manufacturer can choose the thickness and some of the performance characteristics of the steel. The options depend on what the steel manufacturers are selling, and price.
The shortage or unavailability of chains for purchase in 2021 was attributed to delays in production and transportation of materials.
Modern chains are as light as feasible; the link plates are thin. They are not as strong or durable as possible. There is no industry standard for the necessary hardness and tensile strength of the steel. Chain manufacturers order sheet steel by thickness – they trust the steel mills to supply steel that meets the chain maker’s specified standards. Chain manufacturers will market some chains as having been hardened more and better, or coated. Some chains are better than others. Bike manufacturers and bike shops disclose the name of the chain manufacturer; a high value chain may be a marketing point. Even cheap and shoddy chains work for hundreds of hours. Few modern chains are good for more than a few thousand Km – durability varies with chain material, riding conditions, lubrication and cleaning practices. Bike manufacturers trust the chain manufacturers. Consumers trust the manufacturers and the market.
Pitch is standardized. The width of chain links varies. It is generally proportional to the number of cogs on the cassette on the drive wheel. The spaces between cogs in modern systems are so narrow that shifting is only feasible with indexed shifters and carefully adjusted rear derailleurs. Cleaning the paste of lube and dirt out from between cogs requires narrow tools. Older tools for cleaning a cassette may not fit. It isn’t necessary to resort to butchers twine to floss debris out of the spacesbut the changing number of cogs has made some tools obsolete.
Bicycle chains for derailleur systems with 11 or 12 cogs on the rear cassette, measured by internal or external width:
- internal – 11/128 inches = 2.2 mm;
- 11 cog – 7/32 inches; 5.5 to 5.62 mm;
- 12 cog – 13/64 inches = 5.3 mm.
Bike manufacturers buy chains and install the chains on new bikes. Even where the bike manufacturer uses a Shimano or other brand name drive train component set (crank arms, chain rings, derailleurs, rear cassette), the chain may be by another manufacturer. Bike manufacturers have begun to change their “current” models almost annually.
Component manufacturers and bike shops suggest a chain should be made by the same brand as the rest of the drive train. This seems to be a myth. Most chains have standard dimensions.
Bike, component and chain manufacturers expect consumers to accept chains which have limited durability. Purchasers of new bikes may have to replace or upgrade the chain frequently. The use of light chains made of cheap material is planned. Whether bike manufacturers follow a strategy of planned obsolesence might be debated. The bike, component and chain manufacturing industries think bikes and chains have have a short service life. They accept a short mean time before failure for chains, and sell bikes with chains they expect to fail within a few thousand Km. of use.
Bushed and Bushingless Chains
For most of the 20th century, the bushed or bush roller chain was common on bicycles. Bushed chain has become less common, but is being used for some e-bikes as of 2021-22.
On a bushed roller chain the rollers rotate on bushings around pins. The pins attach the plates on the outer links; the bushings fit between the inner link plates. The rollers fit around the bushings.
There are two types of links alternating in the bush roller chain. The first type is inner links, having two inner plates held together by two sleeves or bushings upon which rotate two rollers. Inner links alternate with the second type, the outer links, consisting of two outer plates held together by pins passing through the bushings of the inner links. The “bushingless” roller chain is similar in operation though not in construction; instead of separate bushings or sleeves holding the inner plates together, the plate has a tube stamped into it protruding from the hole which serves the same purpose. This has the advantage of removing one step in assembly of the chain.
The roller chain design reduces friction compared to simpler designs, resulting in higher efficiency and less wear. The original power transmission chain varieties lacked rollers and bushings, with both the inner and outer plates held by pins which directly contacted the sprocket teeth; however this configuration exhibited extremely rapid wear of both the sprocket teeth, and the plates where they pivoted on the pins. This problem was partially solved by the development of bushed chains, with the pins holding the outer plates passing through bushings or sleeves connecting the inner plates. This distributed the wear over a greater area; however the teeth of the sprockets still wore more rapidly than is desirable, from the sliding friction against the bushings. The addition of rollers surrounding the bushing sleeves of the chain and provided rolling contact with the teeth of the sprockets resulting in excellent resistance to wear of both sprockets and chain as well. There is even very low friction, as long as the chain is sufficiently lubricated. Continuous, clean, lubrication of roller chains is of primary importance for efficient operation as well as correct tensioning.Wikipedia on Roller chain, July 2021
The bushingless innovation was widely adopted by designers and manufacturers:
… 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.Wikipedia article on Bicycle Chain
The bushingless chain was developed by Sachs under the Sedis brand and introduced in 1981. It was adopted by SRAM, which initially had been a mountain bike component manufacturer, and became popular in the chain and bike manufacturing industries. The side plates of the inner links are formed into half bushings or shoulders. The roller rides on the half bushings. The pins go through holes in the outer side plates and the half bushings and hold the links together. The outer plates overlap and turn against the inner plates. The plates turn on the pins where the pins go through the plates. My photo of an outer and inner link (left over after I had shortened my new bushingless SRAM chain for installation) shows these features. The hollow pins used in this chain connect the outer links – an outer link on the left. The pin on the left is still partially displaced by the chain breaker tool (there is no roller on that pin – the roller stayed in inner link which was used to close the chain with a master link). The inner link on the right has been pried open to release its roller and show the bevels. The (small) magnification of my smart phone camera shows what the surface, which appears to be perfectly smooth and shiny, are actually rougher. The roughness does not affect the travel of the chain over the cogs. Lubrication is supposed to affect the articulation of the plates, rollers and pins at the ends of the links.
Sheldon Brown and John Allen said:
The inner side plates of a bushingless chain are three-dimensional. Instead of having a simple hole at each end with a bushing pressed through it, each inner side plate hole has a protruding shoulder that amounts to half of a bushing. Since the side plates have an inside and an outside determined by the existence of the shoulders, they can also have bevels on the inside edges without further complicating the manufacturing process. These bevels permit the chain to run more smoothly when it is not perfectly lined up with the sprocket than a conventional chain with flat inner plates. They probably also improve shifting performance.
Since the “bushing” of a bushingless chain is made up of two halves that don’t connect directly with each other, this type of chain is more flexible sideways than a conventional chain. This is because the two halves of the “bushing” have a bit of “wiggle room” with respect to each other.BTI (Sheldon Brown site), Chain Maintenance
The holes in outer link plates are smaller than the holes in inner link plates. The holes in inner link plates are punched to create the protruding shoulders which serve as partial or “half” bushings. The flexibility of chains was engineered by swaging (shaping the pins into barrels rather than perfect cylinders). Modern bushingless chain is more vulnerable to stress and wear than other designs:
The lightweight chain of a bicycle with derailleur gears can snap (or rather, come apart at the side-plates, since it is normal for the “riveting” to fail first) because the pins inside are not cylindrical, they are barrel-shaped. Contact between the pin and the bushing is not the regular line, but a point which allows the chain’s pins to work its way through the bushing, and finally the roller, ultimately causing the chain to snap. This form of construction is necessary because the gear-changing action of this form of transmission requires the chain to both bend sideways and to twist, but this can occur with the flexibility of such a narrow chain and relatively large free lengths on a bicycle.
Chain failure is much less of a problem on hub-geared systems (e.g. Bendix 2-speed, Sturmey-Archer AW) since the parallel pins have a much bigger wearing surface in contact with the bush. The hub-gear system also allows complete enclosure, a great aid to lubrication and protection from grit.Wikipedia on Roller chain, July 2021
The load bearing areas of a bushingless chain are smaller than the load bearing areas of a bushed chain. Bushingless chains have tiny internal voids around the middles of pins where the half rollers on each side end. Lubricants applied to the outside of a bushingless chain flow differently than lubricants applied to bushed chains.
Master links, devices that replace a single outer link, were noted in the BTI (Sheldon Brown) glossary. Master links for chains for single speed drive train chains were, apparently, rare. A few custom metal fabricators made and sold universal master links for derailleur shifting chains by any manufacturer on the market by the 1990’s – e.g. the Craig Super Link. A few other universal links came on the market. The manufacturers were small or fabricated the devices in limited quantities. Some non-proprietary or univeral links are on market or in use.
The master link makes removing a chain for cleaning, maintenance and replacement easier.
Chain manufacturers developed proprietary links for some of their chains. One of Shimano’s systems secured the master link with a special pin. Some manufacturers had three part links – 2 different link plates and a third spring plate to slide over the pins and clip the links. Connex/Wipperman still sells this kind of link.
The more common modern master link is a two part system. Each part is one link plate with one solid pin riveted to the plate. The pins are machined with a grroove or slot at the free end that fits into a machined slot and hole in the opposite plate. Connex Wipperman uses curved slots for some models, and straight slots for others. Many manufacturers have one straight slot model in each size. For intance see the YBN product. These two part systems depend on getting both pins into the opposite slots and locking the link. Two part master links are made by Shimano, SRAM, YBN, KMC and others. The manufacturers name their master links – the names may cause some confusion. Many are sold as single use products.
Some master links made by chain manufacturers may be used on other chains, if the chains are built to the standards of the pitch and width for compatibility with the number of cogs on the cassette on the drive wheel (i.e. links are machine to work on “11 speed” chains exclusively). Some manufacturers market links as compatible with other manufacturers’ chains of the same size – e.g. YBN. Others insist on branded links for their branded chains.
Most two part master links are sold as “single use”. YBN’s 2 part master links, labelled Safe Sections and QRS (Quick Release-Safety) are sold as safe for five uses. If a master link is not properly installed, it may fail – not necessarily instantly. The finely machined slots are vulnerable to microscopic, nearly invisible wear, fatigue and stress. Riders commonly reuse master links.
Removal and Locking
Many cyclists never remove a master link. Some users only remove a master link to replace a chain. The risk of the failure of a master link is real. Often failure is caused by improper installation. It is sometimes caused by wear of the finely machined slots in the pins and plates – which can be caused by removing and locking the link too often or damaging the locking slots. se.
At one time removing a master link by hand was hard. Needle nose pliers could be used, but this tool is harder to use with more narrow chains. There are special pliers that can open and/or lock a link. Locking the two part link depended getting the pins into the slots and holding the bike and stepping on a pedal.
A two part master link can be removed with master link pliers, like the Park Tool MLP-1.2, which is sold in bike shops and online for about $17 to $25 US. The Park Tool pliers can be used to lock or remove a master link, and can fit a chain as narrow as a 12 speed chain. There are other master link pliers on the market. Most are bulky or heavy enough that they will not fit in a seat pack. Light compact travel tools are available. Some of the compact tools store replacement links.
The parts of a master link can be easily lost. Master links are durable but vulnerable to wear and stress in places – the slots that hold and lock the pins. Immersive waxing requires removing the chain at intervals of a few hundred Km.
A user trying to remove a link from a chain on a bike will need to deal with by the tension in the chain caused by the rear derailleur spring. When the link is released and pins are clear of the slots, the chain can snap, flinging the parts into space. Putting the chain on the smallest rear cog and the smallest chain ring (in 2x or 3x sytems) reduces the tension. The user has to keep a grip on the chain which may be dirty and greasy. Some chain breaker tools have a wire accessory – the thickness of spoke – bent just less than 90 degrees at each end. This can be detached from the tool body and slipped over rollers of links beyond the master link. Some users make such an item spoke with a pieace of scrap spoke (a coat hanger may fit into outer plate links but not inner plate links in 10 speed or narrower chains).
Checking for Chain Wear
The inspection and replacement methods used for industrial machines and motor vehicles – e.g. days or hours of operation or distance – do not work for most bikes and chains. The conditions and the use vary, and are not normally measured and recorded. A chain may show almost no wear for several hundred Km., and then wear rapidly. Chain wear is not linear.
The bike chain and bike tool industries developed tools to measure wear, called chain gauges (or chain checkers). A lot has been written about measuring wear and gauges. Articles by the Australian cycling tech writer Dave Rome on checking for wear, based on discussions with the chain wear expert Adam Kerin of Zero Friction Cycling (“ZFC”), and on other sources):
- Dave Rome at Bike Radar, 2016, How to know when it’s time to replace your bicycle chain;
- Dave Rome at CyclingTips, August 2019 How to check for chain wear: The easy way, the best way, and why. The ZFC measurement methods are explained in this article.
There are videos on chain gauges and other chain tools, and online instructions on using them. Adam Kerin of ZFC has published articles and videos on checking chains, as discussed above. There a videos and podcasts of his interviews. Adam Kerin’s advice on chain gauges, and some of his related advice on maintaining chains, can be summarized:
- get a simple drop-in gauge – know how to use it;
- use a chain checker it when the chain is new, and regularly;
- lubricate the chain regularly and clean it frequently. The cleaning will depend on conditions and which lubricant has been used and will be used next;
- consider checking chains on long rides and the possibility of replacement along the route;
For the ZFC chain wear tests, Adam Kerin used the (expensive) KMC digital caliper chain checker. Adam Kerin says a drop-in metal gauge is a sufficient tool for the rider/home mechanic. Adam Kerin cautions that drop-in gauges must be precisely made in video episode 5 of the ZFC YouTube series. He recommended the Shimano TL-CN42 because it is cut to the exact tolerance, and reliably free of manufacturing errors. The tool was not on Shimano’s US sites in early 2022. Some dealers adverstised at that time. It was out of stock at ZFC as of February, March and April 2022. It was selling for nearly $90 (Canadian) on Amazon. Adam Kerin, without mentioning names, said that many drop-in gauges are cast and finished poorly, and do not measure the short span to the tolerance required. There are several inexpensive drop-in checkers by previously unknown vendors for sale online; several claim to be laser cut – which seems to mean precisely cut and finished.
Dave Rome, the CyclingTips tech editor and correspondent in Australia described the subject of measuring chain wear as “murky” on the Ask the Mechanic segment in the NerdAlert podcast episode recorded February 21, 2022. He noted the Park Tool CC-2 gauge is capable of some precision but is vulnerable to bending of the pins affecting the accuracy of measurement. Park Tool makes several different gauges. He thought the Park Tool CC-3.2 drop-in gauge was reliable for most chains except for some SRAM 12 speed chains.
I have a ParkTool CC-3.2. It sells for about $12 US from US online bicycle supply stores (and for $18 or $35 from vendors in the Amazon market jungle). It measures total elongation – it does not “isolate” the rollers. It has hooks at one end, on each side, to fit against a roller. One side is machined to detect .75% wear. One side is machined to detect .50% wear in chains for 11 and 12 speed cassettes.
Hook to Tip
|.75%||7-8-9-10 speed||≪172 mm|
|.50%||11-12 speed||≅171 mm|
The manufacturer recommends dropping a hook end into an inside link. The user should ensure the chain is taut and the hook is held against the roller. Park Tool says the device can be used at the top or the bottom of the loop (between chain ring and rear cog) – the derailleur spring should be pushing the chain taut at the bottom. This gauge spans nearly 14 pins; the tip can touch or fall short of the 14th roller. A chain is elongated when the tip falls does not rest on the roller at the other end (it is falling short) and drops into the inside of the link. The Park Tool CC-3.2 chain gauge measures a span just over 170 mm. to indicate if the elongation in a span exceeds .50%. In a span of 1/8 of the length of chain the gauge has to detect the difference to a tolerance of .5 mm.
The Park Tool CC-3.2 had fairly clear instructions. I had no context or background on how often to use it, or what the gauge was supposed to do. In 2022, I was wondering if it was accurate. I had a new chain available. My kludge to confirm my gauge was good enough. I tried it on a new chain (making sure the chain was taut). The tip did not drop in, and the tip did not pass the midline of the pin inside the roller the tip was touching. It was working, and reasonably close.