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
Former 6-year bicycle mechanic here.
A bike hub contains bearings that hug the axle of the bike and allow the wheel to spin independently of it, meaning that your wheel can spin while the axle stays in place relative to the frame of the bike.
There are two basic kinds of rear hubs in a bike.
One is just a normal hub without any ratcheting mechanism but has external threads on one side (almost always the right side) that someone can attach a freewheel to. A freewheel is a cassette (gear cluster on a bike) that has a ratcheting mechanism inside. When you replace the gears, you are also replacing the ratcheting mechanism. This is usually what’s used on cheap bikes.
The other is a longer hub that has a “freehub” attached. The ratcheting mechanism and an additional bearing or two are built into the freehub body. The cassette (just the gears this time, not the gears and the ratchet) is placed onto this freehub body. The freehub body can be replaced, but its lifespan is much longer than the lifespan of the gears that you would place on it which would be replaced once a year or so, so it goes longer without being serviced.
You’re correct that it is a ratcheting mechanism that keeps it engaged in only one direction. The clicking you are hearing are the pawls being sprung back into place – the actual “click” happens when they suddenly stop moving once they reach their reset position. The pawls are little teeth-looking things that are spring-loaded to only collapse when force is applied from a certain direction but to stay up when force comes from the other direction.
As for the inside of the hub moving the other direction – the reason you can’t grasp it is probably because this isn’t what’s happening – you’ve been right about the rest of it. The inside of the hub is going to move as long as the bike is rolling, it’s the *outside* of the hub (the freehub body) that stops when you stop pedaling. When you are pedaling the ratcheting action means the cassette and hub are moving together, when you are not pedaling the ratchet allows the freehub and hub to stop moving together which is when you’ll hear the pawls clicking back up after they’re allowed to be pushed down. It’s not moving the *other* direction, it’s just not moving in the *same* direction. It’s not moving at all, but the wheel is still moving relative to it.
A mechanic tip – as a general rule you can tell the quality of the freehub (and thus the bike, unless they’ve only upgraded the freehub for some reason) by how loud the freehub clicks. The louder the better. There are exceptions to this like with other stuff, but if you’re out on the ~~train~~ trail and hear a super loud ratchet in the distance, it’s probably a good bike.
Latest Answers