This article was written in cooperation with Serwis Bajka.
TYPES AND NUMBER OF ENGAGEMENT POINTS OF CLUTCHES IN BICYCLE HUBS
All rear hubs used today in road, gravel and MTB bikes are equipped with a one-way clutch that allows the bike to roll freely after you stop pedaling. Without it, the rider would have to pedal all the time, because the crank would be directly connected to the rear wheel. Such a simplified mechanism works in bicycles with a fixed wheel, used in track cycling. When riding a bicycle equipped with a hub with a clutch, when we are not pedaling, a characteristic ticking or clicking can be heard. This is the sound of the freehub, which is the result of alternately engaging and disengaging the clutch mechanism. The number of these clicks per one wheel revolution is called the number of engagement points, or POE for short. This is one of the basic parameters provided by hub manufacturers. Later in this article, we will take a closer look at this issue and explain how different types of clutches differ from each other and what the number of engagement points in the rear hub means for the rider.
Grzegorz Piątkowski (Serwis Bajka): When I go back in my memory to the distant times of my first real bike, I have no trouble remembering what kind of rear hub I used. Due to availability – 2, 3 decades ago – most of us used Shimano 2 pawl (or 3 in some Dura Ace hubs) clutches. The tedious servicing of freehubs with two rows of tiny balls, adjusting the play with thin shims, silencing with Rohloff oil and the characteristically snapping clutches every now and then were unforgettable. Has 30 years of development brought the expected changes? Let’s check!
TYPES OF ENGAGEMENT MECHANISMS – PAWLS
Two types of engagement mechanisms are most commonly used in bicycle hubs: classic pawls and ratchets.
Grzegorz (Serwis Bajka): The pawl mechanism works on the principle of several (usually 2-6) pawls, mounted on the freehub body, meshing with a toothed ring in the hub shell. The first clutch with a pawl and spring was created at the end of the 19th century in the USA and, interestingly, it was used in the front wheel due to the construction of the bicycle. Since then, the design has remained almost unchanged. Only the number of pawls was multiplied, and – much later – the number of engagement points was cleverly increased by adding notches to the top elements of the pawls.
It is worth noting that modern clutches of this type are (excluding Shimano) easy to service and usually do not require specialized tools. Some manufacturers offer spare parts – springs, pawls, and even toothed rings screwed into the hub shell. Well-designed constructions are durable and can withstand a lot. Interesting were the products of the now defunct Kappius company, in which the number of engagement points could be shocking. Boutique, one of the most expensive hubs in the world – the British Royce – also use classic pawls and titanium freehub bodies.
TYPES OF ENGAGEMENT MECHANISMS – RATCHET
The ratchet consists of two rings that move relative to each other. When the freehub body rotates, the teeth of one ring mesh with the teeth of the other, transferring the drive. This is a solution from the 90s – it was the idea of Swiss engineer William Hügi, who sold it to DT Swiss in 1995. The patent for the ratchet in hubs expired in 2020 and since then other hub manufacturers have also started to use this solution in their hubs.
Grzegorz (Serwis Bajka): I used to have the aforementioned Hügi hub in my MTB bike, which I subjected to weight tuning. Thanks to the SL freehub body, bearings, slimmed-down ratchet and aluminum locknut from the road models, I achieved a result of 223.1 g. And although the shell quickly cracked, the engagement mechanism was reliable.
Remember to use the grease recommended by the manufacturer for servicing and do not overdo it with the amount. I do not recommend stretching the springs to increase the volume of the system, as this may lead to damage. Chris King offers great mechanisms of this type (although recently his products have also been struggling with defects). On the other hand, the eyes of weight weenies have been directed for years towards the products of the Extralite brand, where the ratchet is made of 100% aluminum. Contrary to appearances, with proper maintenance and service, this is a relatively durable solution, considering the ultra-low weight of the whole.
Finally, it is worth mentioning the native manufactory Soul Kozak. Their ratchet assumes the elimination of springs. The rings are pressed against each other by magnets.
WHICH IS BETTER – RATCHET OR PAWLS?
Most people believe that a ratchet is better than pawls. This is probably due to the good reputation of DT Swiss hubs. However, it should be noted that hubs with pawls do not have to be less durable than those with a ratchet and vice versa – the mere fact that a hub is equipped with a ratchet does not guarantee high reliability. Not all manufacturers have succumbed to the “fashion” for ratchets and many of them successfully continue to stick to this solution in their hubs (e.g. Hope, Industry Nine, White Industries).
Grzegorz (Serwis Bajka): In ultra-light (or poorly designed) pawl freehubs, a common problem is cracking or wearing of the pawl seats. Another ailment is the breaking of the central tensioning spring, or the deformation of individual springs, under the pawls (most often when trying to unskillfully bend them in order to increase the volume of the hub).
In the case of ratchets, problems most often concern the springs pressing the rings and usually stem from poor service or design errors. There are also over-engineered systems consisting of many independent rings, and as we know, the simplest solutions are usually the best. While servicing DT hubs, I noticed that 54T ratchets wear out most often, due to the small teeth (cyclists generating really high power can damage them). The 36T versions seem to be optimal in terms of durability. I currently use a Chris King hub, but I have ridden many top-of-the-line pawl solutions that have performed flawlessly.
THE SIGNIFICANCE OF THE NUMBER OF ENGAGEMENT POINTS – POE
Both discussed engagement mechanisms can have a different number of POEs – most often it is in the range from a dozen to several dozen, although there are hubs with pawls that have over 100 engagement points. The record holder in this respect is the Industry Nine Hydra with 690 engagement points. The more POE, the faster the drive will be transferred to the rear wheel after starting to pedal. The dead spot angle is calculated by dividing 360 degrees by the number of POEs. Therefore, in the case of 36 POE, this angle will be 10 degrees. How important is this for the rider? Certainly, the lack of a “dead spot” is more important for an MTB rider during technical climbs or a gravel rider riding in more difficult terrain. A road cyclist riding at a stable pace on the “flat” may not even feel the difference between hubs with twice the number of POEs. A significant disadvantage of hubs with a larger number of POEs is the “kickback” that occurs in full-suspension bikes. The more POE, the stronger the kickback.
Grzegorz (Serwis Bajka): As has been said, a smaller “dead spot” is of great importance in the field. For example, when on a climb we have to lift the front wheel over an obstacle and we want the engagement to take place immediately. On the road during sprints, when we need to quickly transfer power to propel the bike, or in hilly terrain during frequent changes of pace.
Theoretically – the more engagement points, the safer for the hub mechanism and for us as riders. But beware: poorly designed hubs with a high POE can mean a smaller contact surface of the rings (in the case of ratchet systems) and their damage in the event of a sudden application of a large force.
HUB SOUND AND NUMBER OF ENGAGEMENT POINTS
The number of engagement points in the rear hub can strongly influence the sound made by the working clutch. It is difficult to give specific data, because the volume of its work depends on several factors – the design of the hub itself, the amount and composition of grease in the mechanism and, to a large extent, on the material and height of the rim profile. However, hubs with a larger number of POEs are usually louder, and the sound they make has a higher frequency. Fans of loud hubs outweigh the supporters of quieter ones and this is probably the main reason for the popularity of engagement mechanisms with a larger number of POEs. In terms of volume, among the hubs available on the market, the Ukrainian Trailmech hubs equipped with the patented Vortex mechanism lead the way.
Grzegorz (Serwis Bajka): From my experience, the most important factor for hub volume is the way the hub shell is machined, its size and material thickness. In addition, the sound is additionally amplified if you use one-piece cassettes such as SRAM or Garbaruk, and also – as mentioned – high rims. All this, as in the case of a guitar, is a resonance box.
The number of engagement points does not always go hand in hand with loudness. Suffice it to mention the oldest DT Swiss hubs from the 90s with 18 engagement points, which were much louder than those offered today. Strong pressure is also important (hence the simplest “tuning” consisting of stretching the springs), but too strong will cause the freehub to drag and / or wear of the mechanism.
ARE THERE QUIET HUBS?
The American company Onyx produces hubs with a unique type of clutch called a sprag clutch. From a technical point of view, it is a one-way bearing that engages under the influence of friction. This mechanism is very quiet – it makes a barely audible hum when coasting with the crank stationary. Its advantage is the engagement angle, which is 0 degrees, so there is no dead spot. The disadvantages are higher weight than in the case of more traditional solutions and higher price. If you are annoyed by the loud freehub in your wheels, you will probably be pleased to know that we cooperate with Onyx and we can build any wheel model from our offer on their hubs.
Grzegorz (Serwis Bajka): I can only agree with the above and add that Shimano silent hubs were quite popular in Poland at one time. I am talking about freehubs with a roller mechanism, i.e. Silent Clutch. Although it was a heavy solution, its durability (with proper service) was at a high level. An additional advantage was a significant reduction in dead spot compared to classic solutions. Maybe some of you still have this type of hub?