We know, there’s no such thing as a stupid question. But there are some questions you might not want to ask your local shop or riding buddies. AASQ is our weekly series where we get to the bottom of your questions – serious or otherwise. Hit the link at the bottom of the post to submit your own question.

This week we are joined by hub design experts at Tairin Wheels, Onyx, TrailMech and Stan’s NoTubes, to take on a reader’s question about silent hubs. Aside from the absence of the sound of a swarm of angry wasps (which many folk are into), what are the actual benefits, if any, of a silent rear hub? Your contributors are as follows:

Are there any advantages to a silent hub? Brands are going to great lengths to make quiet or completely silent hubs, but are there actually any durability advantages, or drag reduction to benefit from as a bonus?

Tairin Wheels: While there aren’t many designs of completely silent hubs out there compared to the abundance of ratcheting hub designs, a silent clutch design can be approached in many different ways. Aside from the benefits of being silent when freewheeling, one of the goals for a silent clutch design is to reduce the wear in the engaging mechanism, should it be a roller clutch, sprag, or an interference clutch with retracting elements.

tairin silent hub

Tairin has a silent star-ratchet hub under development that will use an interference mechanism with retracting elements

The ratcheting you hear on standard hubs comes from the potential energy stored in the pawl or ratchet spring converting into kinetic mechanical energy in the form of sound waves. The first and most obvious observation is the energy loss, referred to as friction in the clutch against freewheeling; but another occurring consequence is wear at the point of contact. If the ratcheting element/geometry is the same used for engaging and torque transfer, eventually, at some point there will be significant wear to impede or lower the torque transfer rating. A slipping ratcheting mechanism most often leads to complete failure soon after.

For those that would say that they never had problems with wear on their mechanisms or ratchet rings, the effect of wear is more evident the smaller the teeth, the higher the engagement points in a revolution.

An interference mechanism with retracting elements is the approach we take in our upcoming silent hub design, where we separate the friction bearing element out of the engaging mechanism, with the benefit of silent freewheeling. Interference mechanisms, like seen in all ratcheting designs, offer the best weight to strength ratio for torque transfer. This is especially true in face gears (star ratchets), which are fantastic when the teeth are of adequate size, but can suffer from wear failures at a higher teeth count per same ring diameter (higher POE) just from freewheeling. With an initiator/retracting mechanism, the wear of the teeth is spared.

Onyx: There can be many advantages to a silent rear hub. Some of the feedback we’ve gathered over the years has aimed at silent hubs offering a more pleasant ride and connection with nature on the trail. This also allows the rider to hear all the other noises on the bike, albeit good and bad, such as tires working, suspension moving, brakes rubbing, and even cable rattle against the frame. 

onyx sprag clutch hub mechanism shell cut away profile section

An Onyx hub with the hub shell cut away to reveal the sprag clutch engagement mechanism, silent while freewheeling with instant engagement upon pedaling

The mechanical relation to a silent hub is usually the drag coefficient of the engagement system. At many times the rider is coasting/freewheeling and many high engagement hub systems have a large amount of drag in this motion from the pawl/ratchet assemblies moving over their engagement teeth. On the Onyx Design, the Sprag clutch glides on a smooth surface which provides minimal drag and gives the byproduct of silence. A lack of drag helps riders sustain speed and efficiency when freewheeling. Durability would not be related to the noise in our hub, but it may be on other designs.

onyx sprag clutch silent instant engagement hub internals

TrailMech: One must be clear about what the term “advantage” means in this context. We will stick with these two: durability and reduced drag. And in both cases, there is no universal answer. It depends on the design. It is not possible to derive these characteristics based on a single attribute: silence. Indeed, it is also a characteristic of the design – whether the hub is silent or not.

Recently, there was an attempt to introduce retractable “ratchets”. That is, to completely remove whatever contact may be between ratchet parts in the disengaged mode. If there is progress with this approach – drag will be lower, compared with similar ratchet designs. Durability? Hard to say. One can think that ratchets themselves will do better. Possible, yes.

What about that retracting mechanism? How durable it will be? What about ratchets: how well they will operate? Especially at the “about to engage” point? Without an in-depth analysis of a particular design and its embodiment, it’s hard to tell.

trailmech vortex engagement design

TrailMech hubs run on their proprietary Vortex Ring Technology. Its durability is derived from the hardness, friction, and wear characteristics of the specially treated steel it is made from.

On the other known design, there is a one-way bearing type. If one were to use bearings theory, drag losses depend on the bearing’s diameter. It is not the only component, but it does contribute there. The larger it becomes the greater the resulting drag losses. The diameter of such mechanisms is comparable, or larger, to the size of a typical bearing used in rear hubs. Thus, it’s like an extra bearing that one needs to account for from a drag loss perspective. We haven’t done our own study to suggest any real comparative data.

In our view – it is not obvious, to say the least, that such designs bring a benefit there. What about the durability of such designs? Even though hardened steel is the material of choice there, it still wears out. And we all know that weight is an important factor. Thus, making a part “beefier” as a way to drive up durability is hardly an option. Wear hardening caused by normal operations gradually kicks in. It may not render the part unusable but will affect performance. E.g. engagement angle increases over time. Again, one needs to put things into perspective. These systems are durable in our view. At the same time, we do not consider that the design “per se” offers higher durability.

Stan’s: The main appeal of silent hubs seems to be creating a more quiet, natural riding experience. How you go about making a hub silent depends on engagement type, subtle design features, and component qualities. Some quiet hubs drag more than some loud hubs, and there’s no actual correlation between noise reduction and drag reduction or durability.

stans m-pulse magnetic pawls project 321 reduced drag coasting

Stan’s new M-Pulse hub, teased at the launch of their Crest, Arch and Flow rims, utilizes Project 321’s magnetic pawl system said to eliminate freehub drag while coasting, but it is not silent

With the new M-pulse, we didn’t set out to prioritize the sound. We thought some degree of “hub sound” was acceptable, with the main focus on exceptional durability, and relatively low drag. Form followed function for us, and function wasn’t silent.

Got a question of your own? Click here to use the Ask A Stupid Question form to submit questions on any cycling-related topic of your choice, and we’ll get the experts to answer them for you!

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17 Comments
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David
David
4 months ago

The reduced drag is a real thing. My OG Onyx hubs were great for this, and so are the Onyx Vespers I’ve got now. Looking forward to trying out the new Tairin hubs too!

Gary
Gary
4 months ago
Reply to  David

“Reduced drag is a real thing”? Stfu! Baggy mountain bike shorts creat more “drag” than any hub out there. If you’re slowing down because your freewheel has too much drag, you must be going pretty slow to begin with.

Lüttenberg Lüttenberg
Lüttenberg Lüttenberg
4 months ago

I love my TraiMech Enduro hubs, best quality I have found in the last 30 years. I also loved the freewheel sound, which gives a feeling of high quality and top notch manufacturing.
But meanwhile I would like to have it silent. Therefore I’m looking forward to Tairin, hope they can deliver soon.

Jason Etter
Jason Etter
4 months ago

I sure would like to see a test showing how many watts a silent hub saves. Then weights of the top silent and non silent hubs. Companies and the person who write this can make claims all day long. But without context they mean nothing.

Bryan
Bryan
4 months ago
Reply to  Jason Etter

How are you going to measure watts when you are coasting?

AverageJoe
AverageJoe
4 months ago
Reply to  Bryan

I believe MIT did that study several years ago and Onyx hubs were the winner.

Shafty
Shafty
3 months ago
Reply to  Bryan

Uh… you spin the hub..? I don’t see where the confusion is. You measure input forces at the axle and freehub to determine absolute drag. This wouldn’t be complex to test.

It would surprise me if Onyx hubs didn’t come out on top or near it. The sprags and lubricant are expressly designed to be extremely low drag(used in igh speed machine tool spindle bearings, etc).

Rich
Rich
4 months ago

I enjoy using quiet hubs, I wouldn’t expect for a moment to actually reduce any drag due to the tiny size of pawls or ratchet relative to the weight and power being used. Certainly when offsetting that against all the other various weight and aero negatives that these would introduce over the best standard offerings,

Ryan
Ryan
4 months ago

They save no Watts. When your feeling you’re producing no watts, when your pedalling the freewheel is engaged so there are no watts to be saved… or am I missing some part of this?

Jason Etter
Jason Etter
4 months ago
Reply to  Ryan

The standard hubs have drag (that’s what is making the noise). That drag can be measured in watts. Maybe it’s easiest to think of them as “reverse watts”. Or more accurately drag. In theory every bit of drag needs to be overcome (when you start pedaling) by producing your own watts.

alloycowboy
alloycowboy
4 months ago
Reply to  Ryan

@Ryan, because no cyclist pedals 100% of the time, whenever you stop pedaling the freewheel mechanism kicks in and is slowly applying a mechanical braking in the form of frictional losses, the energy from the frictional losses gets disipated ethier as heat or the noise you hear from the free wheel mechanism.

The recent trend in mountain bike hubs with over 50 points of engagement has meant that their are some really draggy hubs currently on the market. Which is okay if you are getting your ass carted up the mountain in a chair lift or a truck but not so wonderful for cyclists trying ride great distances cross country.

Jason Etter
Jason Etter
4 months ago
Reply to  alloycowboy

The question is what constitutes “Really draggy”. Sure, if a hub has 3w of drag compared to one with zero the former is “draggy”. But still such a small number as to be arguably relevant.

I have no data on this (because no manufacturer does any actual testing to back up their claims) but i think some of these high engagement hubs can possibly have less drag than you would think. The pawls have less “hook” to them and use much lighter springs.

Gary
Gary
4 months ago
Reply to  alloycowboy

This makes no sense. If you are “trying to ride great distances cross country” you would be pedaling more than people shuttling or using chair lifts. The supposed horrific, terrifying, soul sucking drag should affect them more. And don’t get so high and mighty about your pedaling. Let the shuttlers do their thing and you can go and be miserable in the woods alone.
If you are really concerned about drag, you’d be looking at aerodynamics, not engagement points.

J-M
J-M
4 months ago

A bit surprise you don’t invite bigger engineering brands to those questions. Mavic did quite some studies and measurement on the topic, Corima did engineered a hub that was freewheeling just spinning 2 of the 4 bearings in the hub, then reducing torque (ok it had other problems but they did quite some thinking). Tour magazine used to measure the freewheel torque.
None of your interviewees present a single number!

Zuke
Zuke
4 months ago
Reply to  J-M

Yeah, no Chris King? They pioneered some the earliest high engagement hubs back in the early 2000’s and are still at it today.

whatever
whatever
4 months ago

LOVE my Onyx hubs on my MTB. Not ready to put them on my road bike due to their weight.

Gregory Q Tillery
Gregory Q Tillery
4 months ago

Gosh Gary, sorry this article made you mad