The Complete Handbook of Bicycle Chainrings

Chapter 1: Understanding Bicycle Chainrings

Walk into any bike shop and you will see chainrings in a dozen shapes, sizes, and prices, from a twenty-dollar steel disc to a three-hundred-dollar carbon aero ring. But beneath the surface, a chainring is a simple, precisely engineered component that performs one task: transferring the force from your legs, through the crank, into the chain, and ultimately to the rear wheel. How well it does this determines not just how fast you accelerate, but how smoothly your bike shifts, how efficiently you climb, and how long your entire drivetrain lasts.

On a physical level, the chainring is a circular disc with teeth machined into its outer diameter. It is bolted, riveted, or otherwise attached to the right-side crank arm. As you push the pedals, the crank arm rotates, turning the chainring. The teeth of the ring interlock with the links of the bicycle chain. This interlocking action is a positive engagement; it does not rely on friction like a car's clutch. When the ring turns, the chain moves with it, pulled forward in a straight line from the top of the ring toward the rear cassette or freewheel.

This straight-line pull is the key to understanding how a chainring converts your pedaling force into motion. The force you apply to the pedal is linear, directed roughly downward. The crank arm converts that downward force into torque, or rotational force, around the bottom bracket axle. The torque is proportional to the length of the crank