I bought my first ever road bike last summer; A second-hand Canondale Supersix EVO.

On a list of satisfying sounds, a freewheeling bike must come near the top. Yet it was only this morning I asked myself, "what makes that sound?".

The Sound

What is it?

That ticking sound is made by a ratchet mechanism. The same mechanism which allows you to stop pedalling whilst the wheels continue to move.

When you pedal, the chain causes the cassette to spin. That cassette is mounted to the freehub, where the ratchet lives.

Why does the ratchet make that sound?

The outer shell of the freehub is lined with teeth (the type you find on any gear). The inner layer (attached to the rear hub) is a wheel with some pawls.

If you pedal hard enough, the cassette (and thus the outer shell of the freehub) will reach or exceed the speed at which the rear hub is spinning. At this point, the pawls lock into the teeth, and the cassette starts powering the rear wheel.

When you stop pedalling, the outer shell stops spinning and the pawls repeatedly pass over its teeth, resulting in that satisfying ticking sound!