Hey, I’ve recently gotten into MTB and started learning the anatomy of a bike.
The rear hub makes a clicking noise when coasting but is silent when pedaling – this is caused by springs or ratchets in the hub either engaging with the rest of the system or going the opposite direction, causing the springs (ratchets) to click.
And here is what I cannot fully grasp: What makes the inside of the hub suddenly start going in the other direction when coasting?
Sorry if my description was somewhat vague but I did my best 😀
Thanks!
In: 23
This is a tricky one… but I’ll take a crack at it.
There’s most definitely a few different designs. I can try my best to explain one popular design with enough detail.
There’s a center ring that the sprocket is fixed to, it has to rotate with the sprocket and chain. That center ring has sawtooth cuts on the sides both facing the same direction.
That center ring spins freely on the rear axel.
Then there’s a ring on both sides of that middle one.
One is just a ring with sawtooth cuts in the opposite direction of the center ring. But it has inner posts that ride inside a channel on the axel. So it has to rotate in unison with the axel, but can slide along the axel.
The other is similar, also sawtooth cuts, but larger as it holds the wheel assembly, and doesn’t slide down a channel along the axel. It only rotates.
The two outer rings are linked with a stretched spring that pulls them together and sandwiches the center ring in the middle.
Because of the sawtooth teeth on the sides of the rings, when a force is applied in one direction the flat faces of the teeth press together rings can push on other rings.
But force in the opposite direction, and the sloped faces of the teeth meet. As those faces are like a ramp, the ring teeth ride up those ramps.
The rings expand apart until the end of all the teeth run out. Then the teeth fall into the groove of the next slot and the spring slaps all the rings back closer together. Click.
The force can be applied to either the center ring, using the pedals, chain, and sprocket. Or similarly force can be applied to the outer rings through the wheel.
The wheel will behave just like the pedals will. In one direction, the ring teeth meet face to face and transfer force. In the other direction, they meet slope to slope and slip past another.
You can see that by flipping the bike upside-down. Spinning the wheel forwards and it’s a lot of slip-click-slip-click. But in reverse it stays engaged and transfers the rotation through the rings.
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