Oversimplified: Freewheels

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April 13, 2015

Pedaling backward while coasting was likely the first "trick" you ever learned on a bike. If you've wondered in the intervening decades why it works, what happens while you coast, or what that clicking sound is, read on for our Oversimplified Guide to freewheels.

How do they work?

A freewheel (or freehub depending) is a ratchet and pawl system. Ratchets produce rotary motion in one direction, but not the other.

In the video above imagine you're backpedaling on a bike that is not moving. The exterior teeth and ratchet (blue) are turning counterclockwise, while the interior pawl and axle (red and yellow) are static. Halfway through, the direction reverses and the ratchet turns clockwise, engaging the pawl which drives the axle and the bike forward.

That's pedaling backward (coasting works the same) and forward on a freewheel bike.

Part names. For clarity we’ve removed the ball bearings.

What's that clicking sound?

That clicking sound is the pawls as they run across each ratchet tooth, sort of like a tiny Wheel of Fortune wheel.

The pawls thread onto the hub body and spin whenever the bike is moving. The ratchet fits over the pawls.

Is louder better?

The volume of the "click-click-click" is the product of many factors. Some higher quality freewheels are louder due to construction techniques or the number of pawls, but some are not. For city riding pay little attention to the idea.

Ready for a pop quiz puzzler?

Now that you know how freewheels work, answer this: what's happening here?

Courtesy Pasquale D'Silva via giphy

If you figure it out, shoot us an email by hitting reply.