Sign up for our newsletter
Freehub is part of a bicycle that allows you to glide, and in some cases, it makes a pleasant clicking sound when you glide. It is also the interface between the flywheel (that is, the rear gear) and the rear wheel hub. Freehubs are mechanically very simple objects, but they perform critical functions and are subject to considerable pressure.
In this guide, we will explain exactly what freehub is, how it works, the different types you may encounter on road bikes and gravel bikes, and general maintenance requirements.
Need some basic knowledge help before you dive in? Go to our beginner's guide to road bike parts.
Almost all bicycles have some form of flywheel mechanism. This clever system allows you to step on the pedals to power the bike, but allows you to slide without continuing to spin.
This is achieved by a ratchet mechanism connected to the rear hub. When you apply force, the ratchet engages and drives the bicycle forward. When the speed of the bicycle exceeds your ability to pedal faster (sometimes called slip-out), or whenever you stop pedaling, the ratchet will disengage.
Keep the pedals stationary when the bicycle is running, and sometimes the click sound is the sound of the ratchet mechanism being disengaged when sliding.
On older bicycles or very cheap modern bicycles, this ratchet mechanism is contained together with the sprocket in a single component called a "flywheel." Then screw the assembly directly onto the rear hub.
In contrast, on modern bicycles, the ratchet mechanism is more likely to be contained in the hub itself. This system is called "freehub". The flywheel containing the bicycle sprocket is mounted on the hub body.
Both systems achieve the same effect. However, the more robust and durable freehub system is now almost universally used on better quality bicycles.
Most hub systems use a combination of spring-loaded pawls on the hub body. These pawls mesh with a ring of fixed ratchet teeth in the hub shell. In the most basic case, this combination of mobile pawl and fixed ratchet is used for everything from zippers to roller coasters.
On bicycles, the ratchet ring in the hub allows the pawls to engage when you step on the pedals. Then, they transmit your pedaling force to the road through spokes, tires and the road.
The pawl performs a dual function. Spring loaded, they will automatically push on the inclined ratchet. When you step on the pedals, they lock in place to transmit power, but once you stop applying force, they disengage and instead let the ratchet teeth slide over them.
Essentially, the hub shell and the free hub body can be joined to form a single entity, or they can be disengaged to rotate at different speeds, respectively. For this reason, it is usually simple to slide out the hub body from the hub itself.
Regardless of the design, the hub and the free hub will be supported along the shaft by bearings. More expensive modern wheel hubs tend to use cassette bearings in both components, often resulting in designs that are easier to disassemble. Another method is to use cup-shaped and tapered bearings, which require more effort to deconstruct, but can be adjusted more widely.
Different wheel hubs use different bearing arrangements to balance and support the load pushed through the wheel hub while maintaining a low weight.
The number of pawls and ratchets in the hub may also vary. Wheel hubs always have at least two pawls, while some have as many as six.
These, combined with the number of ratchets in the hub shell, provide you with the number of possible engagement points, that is, the number of different locations where the drive engages.
The more joints, the faster the hub will begin to transmit power once you start pedaling. The maximum angle the wheel can rotate before being driven forward is called the engagement angle.
The engagement angle of a hub with two pawls working together and a hub with 36 ratchets is 10°; this is because a full 360° rotation of the wheel divided by 36 ratchets equals 10°.
However, as the number of ratchet teeth increases, each tooth becomes smaller. At some point, these ratchets become too small to support the power generated by the rider. Therefore, the best hub can strike a balance between quick engagement and stable power transmission. Some pawl designs distribute the load to multiple teeth at the same time.
This basic arrangement of ratchets and pawls can take many forms, all of which can ultimately accomplish the same job.
For example, on some Mavic wheels, the traditional position of the part is reversed. It can be seen that the pawl is connected to the main hub and the ratchet is contained in the free hub.
Different types of ratchet mechanisms are also increasingly used. A common type on high-end wheels is the star ratchet.
This design eliminates the pawl and instead pushes two matching spring ratchet rings together. Turning in one direction, the driver engages, and then turning the other, the rings slide over each other due to the angled teeth. Promoted by DT Swiss, the potential benefits include simpler, easier maintenance and higher reliability.
As mentioned earlier, a key function of the freehub main body is to accept cassettes. The gears are slid onto the splines on the outside of the hub body before the lock ring is used to hold them in place.
Annoyingly, not all flywheels are suitable for all hubs, even if they have the same number of sprockets. Shimano and SRAM generally used the same HyperGlide (HG) free hub design for many years, which meant that their flywheels were basically interchangeable before the advent of the 12-speed system.
Always go its own way, the Italian manufacturer Campagnolo uses a different system. As a result of this, the term "Shimano hub body" can refer to either a hub body manufactured by Shimano or any hub body compatible with Shimano or SRAM cassettes.
However, as long as you are going to replace the hub body, any system can use many wheels. If you want to replace or repair the hub on the wheel, you also need to be aware that you need specific parts that are compatible with the hub, because most parts are not interchangeable.
As the number of sprockets on the average flywheel increases, the space allocated to the hub body also increases. The earliest Shimano hub system had a short pitch and was only suitable for 7-speed cassettes. However, most hubs in use today use free hub bodies that can accept 8, 9, 10, and 11 speed cassettes.
Please note that once the cartridge is in place, you may need to use appropriate spacers to fill the remaining space.
Although older systems enjoy a high degree of cross-compatibility, the pursuit of more gears means that some of the latest systems have abandoned the traditional hub design.
Playing tricks allows the kit manufacturer to install more sprockets so that sprockets smaller than the minimum 11-tooth size can be accommodated on a standard diameter free hub.
Happily, although Shimano now uses a system called Microspline on its 12-speed mountain bike products, its 12-speed road kit still uses traditional splines.
This means that most of us will be able to install their latest 12-speed Dura-Ace and Ultegra kits directly onto our existing wheels. The trade-off is that 11t is still the smallest sprocket.
Shimano also introduced a new 12-speed unique hub design when its latest kit was launched, so although 11-speed wheels are usually compatible with 12-speed kits, the latest Shimano 12-speed wheels are not backward compatible with 11-speed kits. Confusing, eh?
Functionally, SRAM and Shimano hubs were the same before the 10-tooth gear and 12-speed components appeared and were confused. Just like their tapes, both use the same spacing and spline design, making them almost interchangeable. Sometimes wheels are listed as SRAM and Shimano compatible; however, if the wheels use conventional flywheels, you can assume that Shimano compatible wheels are also compatible with SRAM.
The up to 11-speed SRAM hub body uses the same multifunctional HG design, which was first patented by Shimano. However, starting from the 11th speed, things have become more difficult. Some SRAM 11-speed kits use the HG standard.
However, those with smaller 10t smallest sprockets now use SRAM's XDR driver. This design is licensed for free and occupies the same space as an 11-speed HyperGlide road drive, but allows the use of smaller 10-ton sprockets. It can usually be retrofitted to your wheels, and the process of installing and removing the flywheel using chain whip and lock ring tools remains the same.
As mentioned above, some SRAM 11-speed kits will use the XDR standard. However, all its 12-speed packages adopt this standard. Supporting the company's lighter one-piece flywheel, smaller sprockets and greater overall range is one of the reasons SRAM was able to reduce the size of its road crank sprockets.
Campagnolo uses different sizes of splines and different patterns of lock rings to connect its cassette tapes. Except for making them incompatible with Shimano or SRAM, most other elements remain unchanged. Most wheels can optionally be fitted with a Campagnolo-compatible hub body. Depending on the brand you purchased, this may also be an option at the time of purchase.
Campagnolo's Ultra-Drive standard is compatible with 9, 10, 11 or 12 speed cassettes. If using a 12-speed system, make sure that the starting sprocket is not less than 11t. Campagnolo 12-speed cassettes with a smaller first sprocket will not be compatible.
As the first brand to introduce a 13-speed transmission system, this forced Campagnolo to create a new standard for free wheels. Cleverly, this leap also provides significant backward compatibility.
Therefore, in addition to allowing the excellent one-piece flywheel of the Ekar kit to be connected to the 9t smallest sprocket, the company's new N3W freewheel is also suitable for its 10, 11 and 12 speed flywheels.
This is thanks to a small central spline part that can be expanded by a box-type body expansion ring, which Campagnolo calls the AC21-N3W adapter. An extended lock ring is also required. One advantage is that wheel manufacturers may switch to this standard wholesale from now on.
The first tip for maintaining the hub is to do it in a clean, well-lit area with instructions for use at hand.
In other words, the complexity involved may vary greatly depending on the design of the wheel. Some systems can be separated and assembled together without tools, and some systems are equipped with lock nuts that require an Allen key or wrench to loosen them.
Older systems may even use cup and tapered bearings that require careful tensioning to eliminate play but allow minimal friction.
Occasional hubs, such as those found on cheap Shimano wheels, are sealed. Although they can be disassembled and replaced, they cannot be pulled apart to obtain a ratchet drill bit.
In other words, by immersing them in oil, you may be lucky to extend their life. An alternative to the permanent sealing system is a series of pawls, springs and retaining clips separated from the hub body. Because of the tendency to close, be gentle and methodical when removing them.
As with many parts, a good idea is to clean and degrease all parts first. This will allow you to check for wear and order any replacement drill bits if needed.
In extreme cases, the pawl or other parts may break, and the spring or clip may shift or begin to lose resilience. Check your description with how it should look.
After removing the free wheel hub from the axle, now is the perfect opportunity to check whether the bearings in the two components are running smoothly. If you can detect any unwanted movement or grit, they may also need to be replaced.
The seals may come off or deteriorate, so check these too. Assuming everything is in order, find the correct type and weight of grease or oil and apply it where needed. Similarly, the instruction manual is the most important tool here, and it is usually best not to lubricate.
Looking for more bike suggestions? Go to our how to use section for a detailed guide to all aspects of road bikes and gravel bikes written by a team of Cyclist experts.
The mountain bikes of the Jumbo-Visma team are light and strong. Who would have thought about it?
The lightest gravel bike in the world, Specialized S-Works Crux is a real off-road race
Variable geometry allows FiftyOne Assassin to excel in versatility
Six top turbo coach trainings to...
The ultimate gift guide for...
Sign up for a cyclist subscription here.
Sign up for BikesEtc subscription here.
Buy cyclist goods here.
Sign up for the cyclist newsletter here.
How Mark Beaumont won the tough off-road end-to-end race
The last Rapha Gone Racing movie of the year will premiere at 20:00 GMT on Monday, December 13.
Research conducted by Fiona Kolbinger and his team shows that swelling is common in super bike hands
Copyright © Cyclist Holdings Ltd 2021. all rights reserved. Cyclist™ is a registered trademark.