The Complete Handbook of Bicycle Chains

Chapter 1: Understanding Bicycle Chains

A bicycle chain is not a simple loop of metal. It is a precision-engineered power transmission system that must efficiently transfer torque, accommodate angular misalignment, and articulate millions of times under high load and abrasive conditions. Understanding how it works internally, and how its design interacts with the rest of the drivetrain, is a prerequisite for making intelligent purchasing decisions, diagnosing obscure noises, or offering credible professional advice. If you don't understand what the chain is doing, you can't predict its failure mode.

The fundamental function of the chain is to convert the rotation of the chainring into rotation of the cassette sprocket. The chain is a flexible tensile element that wraps around two or more toothed wheels. It transmits power via tension, not compression or friction like a belt. The force is applied to the chain by the engaged chainring teeth and carried along the top run of the chain to the cassette, where the sprocket teeth pull on the chain. The terms "chainring" and "sprocket" are distinct; the chainring is the front, usually larger, driven element, and the sprocket is the rear, usually smaller, element. The ratio of the number of teeth on these two elements determines the mechanical advantage. Bike manufacturers publish gear ratios, but the chain is the critical link in that equation.

The chain is an assembly of discrete links held together by pins. The standard bicycle chain is a "bushingless" roller chain, an evolution of the older roller chain