Freecoasters
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A freecoaster is a bicycle hub that permits a bicycle to be rolled backwards without causing the pedals to turn.
When pedaled forward, freecoaster hubs allow coasting in a manner similar to hubs equipped with a freewheel.
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[edit] Types of coasters
There are two basic types of coasters.
The first is the coaster brake. On this one, if you pedal backward, the hub will lock up. These were generally fit onto kids bikes and low quality adult bikes. They can be modified to work just like a regular BMX Specific coaster. The next type is the BMX specific free-coaster. This works nearly identically to the coaster-brake, but you can back pedal without any binding. They are also generally built to a more strict quality and offer greater performance. There is a third hub that is commonly referred to as a coaster brake, however it is not. These are internal transmission hubs. It does lock up when you back pedal, however, if you were to roll backwards, it would not coast freely, thus it is not a coaster brake.
[edit] The main components of a coaster
There are a few aspects of the free-coaster that must always be present (items in bold are necessary to a free-coaster):
- Hub shell
- Driver (The piece that has teeth attached to it for your chain to run on)
- Clutch (The piece that will either engage or disengage, from the hub shell, depending on the movement of the driver).
- Resistance (There must be some kind of resistance, usually a spring, against the axle so that the hub can “tell” the difference between pedaling forward and rolling backward).
- Axle
- Bearings
- Nuts (or sometimes bolts) and washers (need to be there for almost any hub)
[edit] How they function
The typical free-coaster works on a screw mechanism.
The driver will have a screw shape coming off it into the hub. And the clutch will have it on the inside, so that when the driver is turned, the clutch will move in toward the diver.
But what if the clutch just moves forward with the driver(you might ask)? Well, that is the work of the resistance. In most coasters this resistance is created by a spring running along the axle. The spring will prevent the clutch from moving forward easily with the driver, so the threads on the driver will pull the clutch in toward itself.
As it moves toward the driver, ridges on the clutch will come into contact with the hub shell and turn it with the whole mechanism. The harder you crank down the more the clutch will push into the shell and pull it forward.
When you stop pedalling, the forward movement of the hub shell will push the clutch slightly back off the driver threads and disengage the hub. In this way, the clutch never moves unless the driver moves, so the hub shell is free to move in either direction with out binding.
[edit] Tension and slack
According to George French of G-sport:
Slack is the rotational gap between the clutch being fully disengaged and fully engaged, measured in fractions of a turn either at the crank or rear sprocket. For example, a typical cassette might take up to a 1/20th of a revolution to engage, while a typical coaster might take 1/8th of a revolution.
Tension is the amount of drag on the free-coaster driver. In a KHE free-coaster, for example, this is applied by the little roller ball units. The drag/tension is an essential part of any free-coaster. It holds the clutch element in place while the relative movement of the sprocket activates the clutch to engage the shell. It is typically very small but sometimes it is useful to be able to increase it to stop the cranks spinning etc. I think that the KHE tension can be adjusted by screwing the ball units in and out, but on a typical free-coaster it can only be done by bending the springs out.
[edit] External links
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Tension is the amount of drag on the free-coaster driver. In a KHE free-coaster, for example, this is applied by the little roller ball units. The drag/tension is an essential part of any free-coaster. It holds the clutch element in place while the relative movement of the sprocket activates the clutch to engage the shell. It is typically very small but sometimes it is useful to be able to increase it to stop the cranks spinning etc. The KHE tension can be adjusted by adding on and taking off washers that are on the inside of the hub and flipping around the last washer in the hub, but on a typical free-coaster it can only be done by bending the springs out.
