Most bicycles have a conical cluster of gears hanging off the hub of the rear wheel. Despite external appearances, though, they’re not all the same.
In fact, it is this rear gear cluster that makes up the heart of a bicycle’s derailleur-based drivetrain. The cluster of cogs is called either a “freewheel” or a “cassette.” How do you tell which is which? The major difference is in how it attaches to the rear hub.
New York-based DIY mechanic RJ the Bike Guy shows the major differences in the excellent video below.
To recap:
- A freewheel is a self-contained unit of the cogs and ratchet mechanism that screws onto a threaded rear hub.
- Freewheels make up the heart of the drivetrain of older and/or more affordable bikes that have 5, 6 or 7 cogs, or even single-speed bikes.
- A cassette is a simple collection of cogs that slides into a splined rear hub, retained by a lock ring. The ratchet mechanism is inside the rear hub itself, in a part called the freehub body.
- Bicycles with derailleur drivetrains with 7 to 11 cogs on the rear wheel make use of cassettes and freehub bodies.
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If you wish to use your bike casually around town or to run errands, a freewheel should suffice. It is cost-effective and does not require much maintenance.