A bicycle freehub is a device that allows the rear wheel to spin freely when the pedals are not being turned, but engages the drivetrain when the pedals are turned forward.
As a whole system, it consists of a splined body that attaches to the hub shell, a set of pawls and springs that lock into the ratchet teeth inside the hub shell (mostly), and a cassette that slides onto the splines of the freehub body.
It allows the rider to coast without pedaling, as well as to shift gears smoothly and efficiently.
And in the following contents, we will walk you through more details about it.
Basically, we can categorize freehubs based on their different clutching mechanisms or the variation of freehub bodies.
Freehub Types By the Clutching Mechanism
A clutching mechanism is the part of the freehub system that engages and disengages the drivetrain when pedaling or coasting. There are three main types of clutching mechanisms: pawl and ratchet, star ratchet, and magnetic ratchet.
Pawl and Ratchet Freehubs
The most common type of clutching mechanism found in freehubs is the pawl and ratchet system. This mechanism uses a set of spring-loaded pawls that engage with a toothed ring inside the freehub body. When you pedal, the pawls are pushed outward by the springs and lock into the teeth of the ring, transferring torque to the wheel. When you coast, the rotation of the ring pulls the pawls inward, allowing them to skip over the teeth and spin freely.
The number of pawls and teeth on the ring determines the number of points of engagement and the angle of engagement of the freehub. More points of engagement result in faster and smoother engagement, but also more noise and drag. One popular brand that uses the pawl and ratchet system is Shimano. Their freehub systems are known for their smoothness, durability, and compatibility with various cassettes and hubs. Shimano typically offers 36 points of engagement, which translates to a 10-degree angle of engagement. However, their steel or aluminum bodies may be heavy or prone to notching or creaking.
Another brand that utilizes the pawl and ratchet system is SRAM. Their freehub systems, such as the SRAM PG-1130, are known for their lightweight, high performance, and innovative cassette designs. SRAM typically offers 24 points of engagement, which translates to a 15-degree angle of engagement. However, their aluminum bodies may be costly or require special tools or adapters.
Star Ratchet Freehubs
Another type of clutching mechanism is the star ratchet system. This system, popularized by brands like DT Swiss and Chris King, uses two toothed rings that face each other inside the freehub body. When you pedal, the rings are pressed together by a spring and mesh with each other, transferring torque to the wheel. When you coast, the rings are separated by a small gap and rotate independently, allowing the wheel to spin freely.
Similar to the pawl and ratchet system, the number of teeth on the rings determines the number of points of engagement and the angle of engagement of the freehub. DT Swiss, a renowned brand in bicycle hubs and wheels, is known for their reliable, efficient, and customizable star ratchet clutching mechanisms. DT Swiss offers a range of options, with 18 to 54 points of engagement, which translates to a 20- to 6.6-degree angle of engagement. However, their aluminum or titanium bodies may be expensive or incompatible with some cassettes or hubs.
Magnetic Ratchet Freehubs
A newer type of clutching mechanism that has gained popularity is the magnetic ratchet system. Brands like Onyx Racing Products, Industry Nine, and White Industries have developed this system, which uses magnets and coils instead of pawls and springs inside the freehub body. The magnetic ratchet system offers fast and efficient engagement, but it may be costly and heavy compared to other systems.
The magnetic ratchet system works by utilizing the attractive force between magnets and the magnetic field created by coils. When you pedal, the magnets and coils engage, transferring torque to the wheel. When you coast, the magnets and coils disengage, allowing the wheel to spin freely. While this system is not as widely used as the pawl and ratchet or star ratchet systems, it provides a unique alternative for cyclists looking for something different.
Pawl and Ratchet Freehubs vs. Star Ratchet Freehubs
We have found what they are in their foundation and functions. So here in this special section, what we will focus on is how either of them differs from the other one, or what either of them is better or worse at than the other one. And here are the lists.
Pawl and Ratchet Freehubs
- Easy to service and repair: Pawl and ratchet freehubs are relatively simple in design, making them easy to maintain and fix when needed.
- Compatible with most cassettes and hubs: These freehubs are widely compatible with different cassette and hub standards, making them a versatile choice.
- Affordable and widely available: Pawl and ratchet freehubs are generally more budget-friendly and can be found at most bike shops.
- Low engagement speed or accuracy: Pawl and ratchet freehubs tend to have lower engagement speed compared to other options, which can result in a delayed response when you start pedaling.
- High noise or friction: The engagement between the pawls and ratchet can generate a noticeable clicking or buzzing sound, which may not appeal to some riders. Additionally, over time, the pawls and ratchet can develop wear, leading to increased friction.
- Potential failure under high load or impact: Pawl and ratchet freehubs may not be as resilient to heavy loads or impacts, and the pawls can become notched or damaged with time.
Star Ratchet Freehubs
- High engagement speed and accuracy: Star ratchet freehubs offer incredibly fast and precise engagement, providing an immediate response when you start pedaling.
- Low noise or friction: The absence of pawls clicking against a ratchet results in a quieter and smoother riding experience.
- High load capacity and resistance to impact: Star ratchet freehubs are known for their robustness, making them suitable for demanding riding conditions and heavy riders.
- Difficult to service or replace: Compared to pawl and ratchet freehubs, star ratchet systems can be more complex and challenging to service or replace. Special tools or adapters may be required.
- Incompatibility with some cassettes or hubs: Due to their unique design, star ratchet freehubs may not be compatible with all cassette and hub standards. It’s important to ensure compatibility before making a purchase.
- Higher cost and availability: Star ratchet freehubs often come at a higher price point compared to their pawl and ratchet counterparts. They may also be less widely available, requiring more effort to find them.
Freehub Types By the Freehub Body
A freehub body is the part of the hub that contains the clutching mechanism that engages and disengages the drivetrain when pedaling or coasting. It also serves as the interface between the hub and the cassette, holding it in place with splines or grooves.
There are several types of freehub bodies based on their design, material, compatibility, and performance, such as:
The Shimano/SRAM HG freehub body is the most common type found on bikes. It is compatible with Shimano and SRAM cassettes with 7 to 10 speeds and 11 or 12 teeth (11T or 12T) sprockets. Typically made of steel or aluminum, this freehub body has 8 to 11 splines that engage with the cassette.
The Shimano/SRAM HG freehub body is easy to service and repair. It is compatible with most cassettes and hubs, making it widely available and affordable. However, this type of freehub body may have lower engagement speed or accuracy. It can also generate high noise or friction and may not withstand high loads or impacts.
With the rise of 11 and 12-speed cassettes, Shimano and SRAM introduced the HG-11 freehub body. This type of freehub body fits Shimano and SRAM cassettes with 11 or 12 speeds and 11T or 12T sprockets. It is wider than the HG freehub body and usually made of steel or aluminum, with 8 to 11 splines.
The HG-11 freehub body allows for the use of modern cassettes with more speeds and smaller sprockets. It offers better alignment and stability compared to the HG freehub body. However, it may not fit older cassettes or hubs without the use of spacers or adapters. It can also be heavier or more expensive than the HG freehub body.
Campagnolo is a renowned brand in the cycling world, and they have their own exclusive freehub body. The Campagnolo freehub body is designed for Campagnolo cassettes with 9 to 12 speeds and 11T or 12T sprockets. It is typically made of aluminum or titanium and has 9 to 12 splines.
Campagnolo freehub bodies offer excellent performance, precision engineering, and durability. They provide smooth and quiet operation, along with a long lifespan and resistance to wear. However, they can only fit Campagnolo cassettes or hubs without the use of adapters. They may also be more expensive and less widely available compared to other brands.
SRAM introduced the XD/XDR freehub body for their XD and XDR cassettes. This type of freehub body is designed for use with 11 or 12-speed cassettes and can accommodate sprockets as small as 10T. Usually made of aluminum, the XD/XDR freehub body has a threaded interface instead of splines.
The XD/XDR freehub body allows for a wider range and lower gearing options with smaller sprockets. It also has less weight and drag compared to other types of freehub bodies. However, it is only compatible with SRAM XD/XDR cassettes or hubs without the use of adapters. It may require special tools or parts for installation or removal.
Shimano Micro Spline
Shimano developed the Micro Spline freehub body for their 12-speed cassettes. It can accommodate sprockets as small as 10T and is typically made of aluminum. The Micro Spline freehub body has 23 splines that engage with the cassette.
The Micro Spline freehub body enables the use of Shimano 12-speed cassettes with smaller sprockets. It offers smooth performance and low weight compared to other types of freehub bodies. However, it is only compatible with Shimano Micro Spline cassettes or hubs without the use of adapters. It may not be as readily available or affordable as other brands.
In addition to the commonly known freehub bodies, some hub manufacturers, such as DT Swiss, Mavic, and Chris King, have their own proprietary designs. These freehub bodies may offer unique features and benefits, such as more engagement points, reduced drag, or less noise. However, they may also have drawbacks, such as higher prices, lower compatibility, or more complex maintenance.
Freehub compatibility refers to the ability of different cassettes and freehub bodies to fit together properly and work smoothly. Cassettes are the sets of sprockets that slide onto the freehub body, which is the part of the hub that contains the ratcheting mechanism that engages and disengages the drivetrain when pedaling or coasting.
Freehub compatibility plays a significant role when you want to replace or upgrade your old freehubs. It affects the performance, durability, and maintenance of your bike’s drivetrain. Having a compatible freehub and cassette ensures smooth shifting, optimal gearing, and minimal wear and tear. On the other hand, an incompatible pairing may cause problems such as poor shifting, skipping gears, slipping pedals, or grinding noises.
And there are several factors that come into play when determining freehub compatibility. If you are thinking about having a new freehub, take a closer look at each of them and check for compatibility.
1. Number of speeds: The number of sprockets on the cassette can range from 7 to 12 for most modern bikes. The cassette’s speed must match the freehub body’s capabilities. For example, a 10-speed cassette won’t work with an 11-speed freehub body. In such cases, spacers or adapters may be needed to achieve compatibility.
2. Design of the splines: The splines on the outer surface of the freehub body need to match the slots on the inner surface of the cassette. Different manufacturers may have varying spline designs, so it’s important to ensure compatibility. Check the design of both the cassette and freehub body to ensure they match.
3. Width of the cassette: The total thickness of the cassette depends on the number, size, and spacing of the sprockets. It’s crucial to ensure that the width of the cassette does not exceed the width of the freehub body. If it does, the cassette may interfere with the frame or derailleur, causing shifting issues. Measure the width of the cassette and compare it to the freehub body’s specifications.
4. Brand compatibility: Different brands may have their own standards and specifications for cassettes and freehub bodies. It’s essential to ensure that the brand of the cassette and freehub are compatible. For example, Campagnolo cassettes have different spline designs than Shimano/SRAM cassettes, so they won’t fit on the same freehub body. Always check the compatibility between different brands before making a purchase.
Overhauling Your Freehub is Vital
There is no doubt that, over time, the freehub can accumulate dirt, grime, and wear. This can cause a range of problems, such as poor shifting, skipping gears, slipping pedals, or grinding noises. By overhauling the freehub, you can keep it clean, lubricated, and functioning properly, ensuring a smoother and more enjoyable ride.
But when should we maintain the freehub?
The frequency of overhauling the freehub depends on various factors, including the type and quality of the freehub, your riding conditions and style, and your maintenance routine. As a general rule of thumb, it is recommended to overhaul the freehub at least once a year or every 5,000 miles. However, keep an eye out for these signs that indicate a faulty freehub and may require more frequent attention:
- The freehub body wobbles or moves more than a couple of millimeters side to side.
- The freehub body does not spin smoothly or makes loud or unusual noises.
- The freehub body does not engage or disengage properly or consistently.
- The cassette or lock ring is loose or damaged.
Now that you know when to overhaul the freehub, let’s dive into the steps and tools you’ll need to get the job done.
Steps and Tools for Overhauling the Freehub
Chain whip, cassette lockring tool, cone spanners, spanner, allen key, rag, brush, oil, grease, torque wrench.
Step 1: Remove the Cassette
- Remove the rear wheel and use a chain whip to stop the cassette from spinning.
- Use a cassette lockring tool and a spanner to unscrew the lockring and cogs.
- Store the cassette and lockring somewhere safe.
Step 2: Remove Axle and Ball Bearings
- Check the freehub for wear and determine if it needs replacing or just cleaning and lubricating.
- Use cone spanners and a spanner to loosen the left lock nut and unscrew the locknut and cone.
- Withdraw the axle assembly, catching the loose bearings on a clean rag.
Step 3: Remove the Freehub Body
- Insert an Allen key into the hollow tube-like bolt on the right side of the freehub and turn counter-clockwise to remove the bolt.
- Use some muscle power if needed to dislodge the bolt.
Step 4: Clean and Lube the Freehub Body and Ball Bearings
- Wipe and clean all parts with a rag or brush.
- Make sure the parts are dry before assembly.
- Use a damp rag to wipe the freehub mechanism, avoiding soaking it in solvent.
- Lubricate the freehub body with a light oil or grease.
- Lubricate the ball bearings with grease and place them back into their races.
Step 5: Reinstall the Freehub Body, Axle, and Cassette
- Reverse the steps from removing the freehub body to reinstall the parts in their original order.
- Ensure everything is aligned and tightened properly.
- Use a torque wrench to avoid over-tightening or under-tightening any bolts or nuts.
Freehub vs Freewheel
We have known that the freehub itself is responsible only for the coasting ability, while the gears are attached to a separate cassette. By comparison, a freewheel is a device that combines the sprockets and the ratcheting mechanism into one unit that screws onto a threaded hub. This means that the freewheel itself is responsible for both the gears and the ability to coast.
We cannot say which one of these working mechanisms is better or worse, because either of them has its advantages and disadvantages:
Some advantages of freehubs:
1. More Gears and Smaller Sprockets: One significant advantage of a freehub is its ability to accommodate more gears and smaller sprockets. This allows you to have a wider range of gear ratios, enabling you to tackle various terrains with ease.
2. Reduced Stress on the Axle: Unlike a freewheel, a freehub places less stress and bending on the axle. This helps prolong the lifespan of your bike’s components, ensuring a smoother and more reliable ride.
3. Fits Different Types of Cassettes and Hubs: Freehubs offer versatility in terms of compatibility. They can be easily paired with different types of cassettes and hubs, providing you with more options when customizing your bike’s drivetrain.
4. Faster and Smoother Engagement: Freehubs have faster and smoother engagement, allowing you to quickly transfer power to the rear wheel. This instantaneous response enhances your pedaling efficiency and overall riding experience.
5. Less Noise and Drag: Compared to freewheels, freehubs produce less noise and drag, resulting in a quieter and more efficient ride.
Some downsides of freehubs:
1. Cost and Accessibility: Freehubs can be more expensive and harder to find compared to freewheels. This is something to keep in mind if you’re on a tight budget or need a quick replacement.
2. Special Tools and Adapters: Installing or removing a freehub may require special tools or adapters. This can add complexity to the maintenance process and may not be ideal for cyclists who prefer a DIY approach.
3. Servicing and Replacement: Freehubs can be more challenging to service or replace compared to freewheels. This is where professional assistance may be necessary.
Some advantages of freewheel:
1. Easy Installation and Removal: Freewheels can be easily installed or removed with common tools, making maintenance a breeze. This is an attractive feature for cyclists who prefer a DIY approach.
2. Cost and Availability: Freewheels are generally cheaper and more widely available compared to freehubs. This makes them a popular choice for budget-conscious cyclists or those in need of a quick replacement.
3. Gear Ratio Flexibility: Swapping between different gear ratios is easier with a freewheel. This can be advantageous if you frequently ride in a variety of terrains or prefer to fine-tune your gear setup.
4. Compatibility with Older Bikes: Freewheels are compatible with older or vintage bikes that have narrower rear spacing. If you own a classic bike, a freewheel might be the better option for you.
Some drawbacks of freewheels:
1. Weight and Durability: Freewheels tend to be heavier and less durable compared to freehubs. This can impact the overall performance and longevity of your bike.
2. Axle and Bearing Stress: Freewheels place more strain and bending on the axle and bearings, increasing the risk of damage or failure.
3. Limited Gear Options: Freewheels typically limit the number and size of gears that can be fitted on the rear wheel, usually up to seven. If you’re seeking a wider gear range, a freehub might be a more suitable choice.
4. Slower Engagement and More Noise: Freewheels have slower engagement and tend to produce more noise and friction. This can affect the smoothness and efficiency of your ride.
How to Convert a Freewheel to a Freehub
After checking all the benefits and downsides that both freehubs and freewheels can bring, if you weigh freehubs against freewheels, here is a section where you can learn about some methods on how to convert a freewheel into a freehub.
1. Using a conversion kit: Some manufacturers offer conversion kits that allow you to replace the freewheel hub body with a freehub body that fits on the same axle. This method is relatively easy and inexpensive, but it may not be compatible with all hubs or frames. Before buying and installing a conversion kit, you’ll need to check the specifications of your hub, axle, frame, and the specific conversion kit you’re considering. Additionally, you’ll need some tools such as a freewheel remover, a cassette lockring tool, a chain whip, and a wrench.
2. Replacing the hub or the wheel: Another option is to replace the entire hub or wheel with one that has a freehub. This method is more expensive and complicated, but it may offer better performance and quality. When choosing a new hub or wheel, you’ll need to ensure that it matches your frame spacing, axle type, brake type, spoke count, and other relevant specifications. You’ll also need some tools such as a spoke wrench, a truing stand, and a nipple driver to complete the installation.
3. Modifying the frame: A third option, although not recommended unless you have professional skills and equipment, is to modify the frame to accommodate a wider hub or wheel with a freehub. This method involves widening or cold-setting the rear dropouts of your frame to fit the new hub or wheel. It is a risky and irreversible process, so it should only be attempted by experienced individuals with the necessary tools such as a frame alignment gauge, a dropout alignment tool, and a vise.