Coaster brakes are very popular; everybody has used one of those old bikes with backpedal brake, sometimes in their life. Right, that’s a coaster brake!
The coaster brake became very popular when bicycles became a mass market; it was a time when economy and simplicity were the most important engineering issues; and the coaster brake fitted the bill.
The working principle is very simple: a metal shoe is pressed against the inside of the hub shell by backpedaling. By applying braking force with the pedal there’s no need of a rear brake lever with its cable;
the fact that the brake is inside the hub leads to other benefits, mainly related to low maintenance requirement.
How it works
(image copright ParkTool)
It is a very simple mechanism: the “driver” is threaded on the hubshell followed by the “clutch” and the brake shoe; so they are free to spin when pedalling or free-wheeling; then the brake shoe is followed by the reaction arm, which is secured on the frame to contrast the torque.
( please note: the hub shown has got a fixed sprocket, but the same principle applies if it had a freewheel).
When backpedaling the driver (usually by an internal thread between it and the clutch) presses against the clutch and that opens the brake shoe. Do you remember? They are free to spin on the hubshell, but now they are pressing against it. This friction gives a high amount of torque that is stopped by the reaction arm… better not say what happens if it is not secured properly to the frame…! 
That’s all, a very simple and reliable mechanism. Let’s summarize the advantages:
But, of course, there are also some disadvantages…
One other disadvantage maybe is that the coasterbrake cannot be used with external gearsprockets?
Well, very often coaster brakes are associated with internal gears.
External gears will give more than a trouble while backpedaling.
Also the Coaster brake, as said, makes more sense in utility bikes where the maintenance has to be low; so external gears with their high demand of maintenance and spares, are not a good idea to associate with coaster brakes.
As far as I know, never seen a coaster brake with cassette freehub
I think that hub brakes are the best thing for children to learn on. In the USA they were standard for all kid’s bikes, and they really turn kids into confident and capable cyclists. When I see a british child cycling, they nearly always have hand brakes. I think this is really dangerous since it requires a lot more coordination and physical strength. There is something a lot more intuitive about backpedaling to stop, and this makes it easier to concentrate on balance, considering what is around you, and steering. Backpedaling is probably a great thing for the elderly or anyone with reduced hand-strength. Your legs are very strong and they can be used to carefully control the degree of braking. It’s really great to read an article about hub brakes. I miss them, and I’d be happy to ride a bike with hub brakes any time.
-jesse
I recently put a 700 x 30 rear wheel with a coaster brake on one of my bikes. The thin tires and somi-aero seating combined with the simplicity of the single-speed coaster brake make this an incredibly fun city bike. I haven’t ridden my other bike once since I put it together!
hi
can i ask how you disable this braking system. my young son keeps pedalling backwards when learning to ride, so need to disable for thie learning period
any help appreciated
James,
The coaster brake is internal in the hub and cannot be disabled. Have you read Jesse’s comment above? Much easier to wait for your son to learn to use the brake.