What is a Freecoaster?
A freecoaster is a bicycle hub that can roll in either direction without the pedals moving.
What are the 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 as if you were using your brakes (though technically you are…). 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.
- Which brings me to the next type, the BMX specific freecoaster. This works nearly Identical 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 refereed to as a coaster brake, however it is not. These are the internal transmission hubs (made by Shimano mostly) 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. I just wanted to add this to clarify.
What are the main components of a coaster?
There are a few aspects of the freecoaster that must always be present (items in bold are necessary specifically to a freecoaster):
- Hub shell (I hope this one was easy enough to figure out)
- 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 (This should be easy enough also. If not, then look up the basics of a hub).
- Bearings (Although a hub could work without bearings, you would have a hell of a time getting it to roll anywhere).
- Nuts (or sometimes bolts) and washers (need to be there for almost any hub)
How do they work?
The typical freecoaster works off of a screw mechanism. The driver will have a screw shape coming off of it into the hub. And the clutch will have it on the inside, so that when you turn the driver, 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 pedaling, the movement of the hub shell forward will push the clutch slightly back off of the driver thread an 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.
According to G (that’s 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 cassett might take up to a 1/20th of a revolution to engage, while a typical coaster might take 1/8th.
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…