The loud freewheels found on above-average and high-end bikes tend to surprise new cyclists. I wasn’t an exception. When I began commuting on a bike, I was often turning my head after bikers whose bicycles sounded like angry robots. I was impressed.
Some may think that the extra buzzing is just for show, but that’s not the case. There are technical reasons why expensive rear hubs produce such great decibels.
Why are higher-end hubs louder than the cheap ones?
The noise produced by a rear hub, cheap or luxurious model, comes from the so-called pawls – tiny, spring-loaded elements designed to bite to the ratchet of the hub when pedaling forward.
When coasting or pedaling backward, the pawls disengage and slide over the engagement surface.
Since higher-end hubs use stronger springs and have a greater number of pawls and engagement points, those models produce louder and more aggressive sounds.
Also, more advanced hubs rely on lighter grease which doesn’t restrict the motion of the springs as much.
I know that this sounds a little complicated. But don’t worry. Further clarification is coming.
Figure 1 illustrates what happens inside the hub during pedaling.
The pawls push out and engage against the teeth of the ratchet. As a result, the wheel begins moving under the dictation of the cyclist.
When the pawls bite to the ratchet, they stop producing sound because they lock against the inner teeth and become immobile.
Figure 2 shows what happens when back pedaling.
During back-pedaling, the pawls start sliding against the inner teeth and go into their “beds” upon coming in contact with a tooth. When the rotation is reversed, they jump out since they’re spring-loaded and bitе again. (fig 1.)
During coasting, the pawls remain stationary, but the ratchet ring slides against them.
The buzzing sound produced by the hub comes from the closing and opening of the pawls plus the sliding of the pawls against the inner teeth.
Pawl Spring Mechanism
The graph above illustrates the operation of the springs under the pawls.
When a pawl is engaged, the spring opens and maintains the position of the pawl.
When a pawl is disengaged, it closes and so does the spring.
The stored tension in the spring pushes the pawl ever so slightly up, and the pawl gently brushes the engagement teeth whenever possible.
The interaction is largely responsible for the hub sound.
More Pawls + More Engagement Points = More Noise
A greater number of pawls in combination with more engagement points results in more movement and consequently noise.
And since more pawls and engagement points equal greater pedaling efficiency, more expensive hubs offer more of those and sound louder as a result.
A Table With Higher-end Hubs and Their Number of Pawls
|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|
|Industry Nine 6-Pawl Driver Body||6|
|DMR 6 Pawl 10 Speed Bolt Through||6|
Why are more pawls and engagement points more efficient?
When there are more pawls and engagement points, the two connect to each other faster and minimize the loss of pedaling power.
You have to spin the pedals very little (think millimeters) before transferring power to the rear wheel.
This type of pedaling efficiency is greatly appreciated in mountain biking because it improves gear shifting while ascending and when making slow and tight turns.
How Loud Are High-end Hubs Really
Hubs such as the Koozer XM 470 reach 74 dB. Meanwhile, Hope Pro 4 is measured at around 60 dB.
Luxury Hubs = Better Machining
High-end hubs are made of better materials and with greater precision.
Moreover, they aren’t painted with the “syrupy” paint common for the cheaper ones. As a consequence, they produce a different resonance and a more distinct sound.
Of course, the materials of which they are made, as well as the rims, influence the final audio output too.
Lighter Hubs = Louder
High-end hubs are lighter too. Their lack of mass minimizes noise-damping – another property increasing the volume.
Less Grease = More Freedom
High-end hubs tend to use less aggressive grease. This practice frees the movement of the springs.
Subsequently, the synergy between the pawls and the engagement surface becomes more fluent and consistent – another technicality that makes higher-end hubs louder than the entry-level ones.
Carbon Rims + High-End Cassettes = Sound Amplifiers
Expensive hubs are rarely the only luxurious part on a bike. After all, it would be somewhat weird to ride a 100-dollar beater equipped with a 200-dollar hub.
If the hub on a bike is high-end, chances are that so will be the remaining parts. Believe it or not, the rest of the components affect the “orchestra” too.
For instance, many people who ride with pro hubs, rely on top tier carbon rims too; those act as a sound system amplifying the noise produced by the rear hub.
The cassette of the bike has a strong effect on the hub’s sound production too. Cheap ones with plastic elements muffle the sound whereas the higher-end models with solid, stiffer, and lighter bodies boost the buzzing of the rear hub.
It’s not uncommon for a hub to get louder upon changing the bike’s cassette with an upgraded model.
Frequently Asked Questions
Does the friction between the pawls and the engagement surface slow you down?
Yes, there’s some drag, but it’s minuscule and practically non-existent when you take into account the weight of the involved parts, the optimized angles of engagement, and the effective greasing.
Besides, drag is present only when you’re coasting or backpedaling – two situations when the rider is not going for limit speed.
Is loudness always an indication of quality? Are all good hubs loud?
No. There are many high-quality hubs that are purposefully silent.
One example would be Shimano’s Scylence – a hub free of ratchets sounds designed to improve the concentration of the rider.
You can see how Scylence works in the video below.
There are also old-school hubs relying on а “roller clutch” system which eliminates the need for a ratcheting system and produces significantly less noise. However, roller clutch models are considered too fragile for extreme riding.
By the way, I’ve also heard of people who purposefully degrease low to medium level hubs prior to selling their bicycles in order to confuse the buyer that the hub in question is “one of those loud MTB hubs”. Be aware.
Are there any other benefits to a loud hub besides efficiency?
Yes – effortless alerting. A loud hub is easier to hear than a quiet one and saves you the trouble of ringing your bell to announce yourself 20 times a day when riding close to other people.
The hub acts as a precautionary alarm too – it alerts people who you can’t even see.
Why is there so much sound variation between different hubs?
The final sound and the rhythm depend on the mechanism, the used materials, and the weight of the hub. Hence why every manufacturer produces hubs with a distinct “melody”.
The classic example would be ChrisKing hubs. They are instantly recognized as they sound like angry bees.
Is it me or are BMX hubs the loudest of them all?
It’s not just you. BMX bikes have some of the loudest hubs on the planet due to their incredibly high number of engagement points – over 100 in some cases.
Moreover, some BMX riders remove the grease from their hubs to amplify the sound even further and win the “who has the loudest bike” competition. The end result is one very noisy skate park.
What are the downsides of degreasing a hub to make it louder?
This hack reduces the lifespan of the hub by increasing the friction between the pawls and the engagement points of the splines. It has no practical value other than to boost the buzzing of the hub.
What are the downsides of a loud hub?
Not everybody likes loud hubs. Some people found them annoying and distracting. But that is more of a personal preference than a direct downside.
- Camouflaging other sounds
From a technical perspective, one of the main shortcomings of a loud hub is that it could overpower other bike sounds indicating mechanical problems.
- Muting the scenery
Loud hubs can mute the surroundings and prevent you from hearing other cyclists, people, or vehicles.
- Anti-stealth mode
If your hub sounds like the exhaust pipe of a motorcycle, you lose the silent power of the bicycle. In most cases, this shouldn’t be a problem, but if you’re passing through an area densely populated with house dogs, they may get irritated and cause problems.
Therefore, if you want to preserve your ability to enter ninja mode when riding, it’s recommended to stay away from angry hubs.
Is a hub’s sound part of its selling points?
For sure. The sound of a hub influences the final purchase more than a non-cyclist or a beginner may think.
Some people prefer silent ones while others search for the loudest and angriest option to assert dominance on the trail or the street. Yes, you read that correctly.
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