Earlier we covered the hub engagement function and design theory. Theoretical view, although abstract it may be, is essential. It is first step before moving on to the practical, and arguable more exciting, part. The guide of various existing hub engagement designs. We will uncover both the well-known and the less known designs. And bring forward the reliability and weight perspective.
Table of Contents
1. Ratchet-and-pawls Mechanism
2. The Star Ratchet
3. The King of the Designs
4. The Scylence
5. The Vortex
6. Noiseless Designs
7. Reliability and Weight
1. Ratchet-and-pawls Mechanism
The POE term originates from the “ratchet-and-pawls” mechanism. Also known as “pawls and a toothed ring”. It has been around for decades. It is the most common engagement design out there. This system uses several steel pawls. They are often integrated with the freehub. Each individual pawl has its own small spring or a magnet. And there is the ratchet ring coupled with the hub shell.
In some hubs, like Race Face’s Vault, Rotaz or the legacy American Classic, the pawls are in the hub shell. Whilst the ratchet ring embodied to the freehub. The principle remains the same, though. Each pawl has one or several teeth. Rotation in one direction makes the pawls teeth mesh with those of the ratchet ring. The system engages. This is the “locked on” mode of it.
In the opposite direction – the teeth of the pawls and of the ratchet ring slide against each other. It is what makes that “clicking” sound of the hub in coasting mode.
This design has countless variants. The number of pawls ranges from two to eight. Whilst the POE from the mediocre 18 to the overwhelming 690. That what Industry Nine Hydra hub offers.
There are many “ratchet-and-pawls” inspired designed out there. With some specifics to the original concept. Like that of Rotor’s Rvolver. Where the toothed ring is not fixed in the hub’s shell. Instead, it “floats” in it. Whilst the pawls themselves have cylindrical shape.
2. The Star Ratchet
In the ratchet-and-pawls mechanism only few pawls transfer all the rotational force. Often there are just three to six of them. Each one carries large part of the total load, though. Other hub engagement designs balance the distribution of the rotational force in a profoundly different way.
The one that achieved tremendous adoption is the “Star Ratchet” by DT Siwss. It all started in mid-90’s when DT Swiss acquired the proprietary technology. Since then, they made it arguably the famous design out there. It is available in several variants for both road and MTB. The main difference, compared with the ratchet-and-pawls, is that there are no pawls. Instead, the system has two parts, often referred as rings. Each ring carrier the identical number of teeth. Their number ranging between 18 to 54. The latter being the top-level version of it.
The large number of identical teeth on the rings distribute the load evenly. They make up a large surface area for the rotational force to work its way through. Each tooth deals with relatively small load, opposite to that one the ratchet-and-pawls. The key difference of design is that the number of teeth on both rings is exactly the same. And that number is a multiple of the number of pawls of the classical design.
The time proved it is a very reliable design. There are number of manufacturers with their hub engagement designs inspired by the Star Ratchet. They are: Absolute Black, ACSE, ACROS, Erase, Extralite, Mavic, Soul Kozak and Syntace. We are not claiming that it is an exhaustive list. The design continues to grow in adoption.
3. The King of the Designs
Chris King’s “Ring Drive” system went even further. King’s design drove the number of teeth up to 72 on both rings. And thus, the POE. Reaching the theoretical 5 degrees of the engagement. At the same time, it is not what sets it apart from the rest. There is one ingenious feature that allows it to operate flawlessly even with so many teeth. It is the “Helical Splines”. In a nutshell Helical Splines provide an extra force to keep both rings locked together. It comes to play when the mechanism is in the engaged mode. Simply put – the higher the load, the stronger the system engages. It is the system that endures and almost defy the wear out. And with the steel made freehub, becomes almost indestructible.
4. The Scylence
Chris King’s ingenuity inspired another recent design – Shimano Scylence.
The Scylence further extends the ratchet-based design concept. It uses the helical splines to retract of the rings in the disengaged mode. Shimano states that it has theoretical 7.6 degrees of the engagement. And that it offers near soundless operations whilst freewheeling. This is rather uncommon. Majority of the quick to engage hubs operate with a distinctive sound in that mode.
A road gear ratio with 50T chainring and 11T sprocket. The effective With such a refined concept the mechanism became complex. There are many small parts. One of the toothed rings is an alloy made. And it carries many tiny teeth, compared with similar parts of other designs. How durable it is on the long run is unclear.
5. The Vortex
Our design – the Vortex, extends the ratchet-based and ring drive concepts step forward. It uses toothed rings, but they are of an unusual conical shape. The teeth are also of a specific profile. Thus, the Vortex features a progressing engagement. That is higher the load, the stronger it engages. The mechanism itself is made of just two parts. It is as simple as it gets.
We have developed several versions, with number of teeth ranging from 50 to 60. With the theoretical 7.2 to 6 degrees of the engagement, respectively.
At present the standard version is Vortex with 50 teeth. All Enduro, Gravel and XCR rear hubs use it.
6. Noiseless Designs
Our design – the Vortex, extends the ratchet-based and ring drive Silent operation is not something unheard-of new in the field of hub engagement designs. These designs were around for years. There are plenty of examples. Long ago discontinued Shimano’s Nexave – also known as the “Silent Clutch”. True Precision Components – Stealth MTB hubs. Or Zipp’s hubs with Axial Clutch system. The latter, like a ratchet-based design, also features two ring plates. Although only one of them has teeth. Whilst the other features special openings to mesh with the teeth of the first ring plate. Zipp’s Axial Clutch has a POE of 36. Which translates into theoretical 10 degrees of the engagement.
The most recent entrant into noiseless designs space is Onyx Racing Hubs. Unlike Zipp’s Axial Clutch or Shimano’s Scylence, there are neither ratchet rings nor teeth. This design relies on friction forces to lock the system in the engaged mode. And it the same concept that True Precision Components hubs have. Another name of such designs is “one-way bearing”. Onyx refers to it as the “Sprag Clutch”.
There is yet another distinctive feature of this design. They have near 0 degrees of engagement. They engage almost instantly. Strictly speaking 0 degrees is the theoretical figure. In practice it is not 0. But for practical purposes they are quicker to engage that most, if not all, other designs out there. We hold that no rider will be able to tell the difference of a fraction of a degree and true 0.
Follow the discussion on Bikerumor on silent hubs to know more about this type of hubs.
7. Reliability and Weight
Our design – the Vortex, extends the ratchet-based and ring drive Efficiency (repeat the point here) was the first quality we reviewed. Reliability and weight are two other factors that influence the evolution of various designs. If not for them, chances are that we still be pretty much OK with the ratchet-and-pawls.
The primary material used in majority of road and MTB hubs are aluminum alloys. Hub’s shells and freehub bodies are examples of an alloy made hub components. For the ratchet-and-pawls hubs this means that the pawls seats experience fatigue. It develops under the normal everyday load conditions. Over time fatigue results in freehub’s failure.
The load level, that hub deals with, is discipline specific. For the road the drivetrain gearing option and ranges remain relatively stable. With the proliferation of 1x drivetrains for MTB and with e-MTBs it is not. The ranges of drivetrains gears grew substantially there. And so is the magnitude of forces under which the engagement operates. It is still expected to operate reliably, though.
Steel or titanium is a material-based approach to improve the durability. And it is works in most cases. The tradeoff is that system’s weight must give in.
Ratchet-based systems distribute the forces over much larger surface area. The load that an individual tooth carries there is way less. It is 6 to 20 times lower, compared with pawl’s tooth. We take that the applied force remains equal. Ratchet-based systems, typically, operate longer. They remain light enough for even the most demanding competitive cycling disciplines.
The “one-way bearing” hub engagement designs have a very specific way of transferring the rotational force. And it rules out pretty much any materials but steel for its core. There is a noticeable weight gap between such hubs and those of other designs.
There are number of various designs on the marker. In our review we grouped them into several types, thought. Choosing the type which is right for you is one of the major decision points. With this overview you are better prepared to make one. Getting you one step forward choosing your hubs.