Chain

Rick Proctor

While riding your bike on a nice day, do you give any thought about what is going on between you and the road?  What are the mechanical wonders responsible for your ride? 

Your feet provide rotational energy into the pedals, cranks, and chainrings.  A chain transfers the energy to the rear sprockets and wheel assembly to drive you and the bike forward.  Modern bicycle chains are the roller chain type with a pitch of ½ inch.  That means the distance from one chain link roller pin center to the next is ½ inch when the chain is new.  The gear teeth on chainrings and sprockets are spaced to match for the chain to mesh nicely as it wraps around the selected chainring and sprocket.  As gear teeth engage the chain, each tooth contacts a roller which ideally rolls a little bit as the gear rotates and the tooth becomes fully seated in the chain.  The force being transferred by the chain is evenly distributed to all the teeth in contact with the chain. 

Considerable amounts of research and development has gone into the shapes of gear teeth and chain links.  Numerous patents define details of the chains and gears commonly used today.  The materials and precise shapes of gear teeth and chain links make a difference in how well they function as a system for best performance and durability per dollar spent.  Bicycle chains are typically made of steel for the preferred qualities of strength, durability, and cost.  Neither aluminum alloy nor carbon-fiber are known to match these preferred qualities as a chain material.  Consequently, chains are heavy, but that’s what it takes to do the job.

The width and side-to-side flexibility of chains vary with the intended use for various gearing schemes.  For single speed use, a very durable chain can be built for no side-to-side flexing if the chainring and sprocket are properly aligned.  A belt could be used in the same application.  When multiple external gearing options enter the picture, the chain must be able to flex side-to-side to shift gears, which is something a belt cannot do.  Typical gearing schemes are 1, 2 or 3 chainrings on the front and up to 12 (13?) sprockets on the rear cassette.  There seems to be a contest between bicycle component manufacturers for who can provide the most gear options. 

A typical bicycle chain can have 112 links, and each link consists of a roller (a.k.a. bushing), a pin, and 2 side plates for a sub-total of 4 moving parts per link.  4 X 112 = 448 moving parts in a chain and they all move on the chainrings and sprockets.  All those moving parts need lubrication to minimize friction and wear.  A well lubricated chain is also quieter than a dry chain.  A chain that rattles or squeaks indicates neglect and may attract the attention of other riders.  It only takes one un-lubricated link in a chain to wear rapidly and weaken to prove the adage “a chain is only as strong as its weakest link”.  As the moving parts of a chain wear the ½ inch link pitch gets a little longer, which also increases wear on the teeth of chainrings and sprockets.  The chain should be replaced when it “stretches” to a certain point to protect the chainrings and sprockets from excessive wear and prevent an unexpected chain failure.

A fair question is what is the best chain lube to extend the service life of your bike’s drivetrain?  I’ve read a few studies that tested and compared various chain lubes.  Numbers for lubricant efficiency, longevity, viscosity, availability, convenience, and cost add up to indicate any chain lube is better than no chain lube, and the commercially available products that sell probably do the job at least acceptably well.  Ask around to see what other riders use, then pick one and use it consistently to free your mind for other thoughts.