from Rookie’s keyboard
Hello, friends
This Wednesday I decided to present to you in great detail what powers the distinct sound of a bicycle rear hub (BRH). Of course, I’m talking about the “buzzing” that comes from the rear wheel when costing.
The Source
The rear hub noise comes from an assembly of tiny, spring-loaded elements that bite against the ratchet of the hub when pedaling forward. Those are called paws precisely because they “grab” a ratcheting ring.
Complicated?
Calm down, bro.
It’s as simple as ABC after you look at a few images and graphs.
Figure 1 shows how a hub behaves during forward pedaling. The pawls (remember that they’re spring-loaded) jump out and engage/bite against the teeth of a ratcheting ring part of the hub body.
That union is necessary to transfer power from the rear cog to the hub. And when the cog moves so does the hub and respectively the rear wheel.
When the pawls are engaged, they remain immobile and thus silent.
Figure 2 shows what happens when pedaling backward.
During backpedaling, the pawls move in the opposite direction, brush against the engagement points, and then go into their beds for a second. That contact and springing are behind the rhythmic sound that you hear.
Figure 3 shows what happens during coasting.
In this case, the pawls remain stationary (the freehub body, driver, and cog aren’t moving), but there rest of the hub continues to spin and with it the ratcheting ring.
Since the paws are stationary, they don’t bite. Instead, the ratcheting ring is brushing against them and pushing them down – similar to what happens during back-pedaling, the only difference is that the circular motion comes from the ratcheting ring rather than the pawls.
The number of pawls and engagement points influences the sound. In general, more pawls and engagement teeth result in a louder buzz.
And since expensive hubs tend to have more engagement points as well as pawls with stronger springs, those luxurious models are often much louder (although not always – sometimes manufacturers “silent” them).
The benefit of more teeth and pawls is the elimination of“dead spots”. For instance, I have a low-end hub on my road bike with only 2-3 “tired” pawls and a very limited number of engagement points.
And there’s a noticeable gap before the pawls bite against the ratcheting ring. Expensive hubs aim to eliminate that so that the rider has more control and experiences no energy loss.
Here’s a table with some high-end hubs and the number of pawls they have.
| Model | Number of pawls |
| DT SWISS MTB 370 | 3 |
| DT Swiss 360 | 3 |
| Hope Pro 4 Disc 6-bolt Boost Rear Hub | 4 |
| Hope Pro 3 Mono Road Rear Hub | 4 |
| Ibis Freehub | 4 |
| Industry Nine 6-Pawl Driver Body | 6 |
| DMR 6 Pawl 10 Speed Bolt Through | 6 |
| CNC Hubs | 6 |
Material and Machining Matter Too
The material and the craftsmanship of a musical instrument influence its sound. Hubs are the same way even though their main purpose isn’t sound production, of course.
Expensive/luxury hubs are more precise and made of higher-grade materials. Also, they have better painting. Believe it or not, paint influences acoustics too.
As a consequence, different hubs have different resonances and a more distinct sound.
Lighter = Louder
The lighter the hub, the noisier it can be because the low mass has a smaller noise-damping effect.
Less Grease = Louder
Hubs lubricated with less aggressive grease are louder because the pawls are freer and grind more.
Some people even purposefully de-grease their hubs to make them louder. The downside of this practice is the decreased lifespan of the hub’s internals.
Rims + Cassettes = Sound Amplifiers
The rim and the cassette increase the sound of the hub. Carbon rims tend to be the loudest.
Cheap cassettes with plastic parts muffle the sound. Meanwhile, expensive models with stiffer, lighter bodies “pump up” the volume of the hub.
Loudness Doesn’t Always Equal Quality
Many top hubs are indeed loud, but silence doesn’t indicate poor quality. Many “boss” hubs are purposefully silent.
For example, Shimano’s Scylence is as silent as it gets to improve the focus of the rider.
Some old-school hubs have a “roller clutch” system that doesn’t use a ratchet and is, therefore, a lot quieter. That said, roller clutch models are too weak for extreme riding.
“Get Out of the Way”
I’ll be real with you. My favorite quality of loud hubs is that they tell people to get out of the way for me.
I am not kidding. If you have a loud hub, you can start coasting when you want to alert those around you of your presence. And the louder the hub is, the more effective the warning becomes.
Of course, this effect has its shortcomings – you are muting the scenery and giving up the option to be stealthy.
The truth is that the sound of a hub and mostly its loudness could be a big selling point. And some cyclists take great pride in having a hub that dominates the audio experience of those nearby.
However, some hubs are so damn loud that I just want to press a mute button on them when a cyclist passes by me. This used to be the case mostly for BMX models and MTBs, but these days even road hubs are in the same screaming category.
And that my friends, is the secret orchestra of the rear bike wheels:
It’s made of pawls with springs and a ratcheting ring.
Buzzzz….
Until next time
– Rookie
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