Heading out the door? Read this article on the new Outside+ app available now on iOS devices for members! Download the app.
For a long time, picking a freehub body was as simple as deciding between Shimano or Campagnolo, but sadly, things are no longer so simple. The increased number of sprockets squeezed into the back, plus the introduction of wide-range cassettes with smaller 10-tooth or 9-tooth sprockets, has seen multiple more variants of freehubs hit the market, and things have quickly become as confusing as selecting a bottom bracket for a press-fit frame. This article is designed to be a resource to ease confusion over freehub selection and cassette compatibility.
This article covers the most common types of freehub bodies on the market today, what differentiates them, and what compatibility they offer.
Please note that the information in this article should be relevant to all common bicycles purchased from the 90s and onwards. Before this time, bikes are likely to feature now-defunct fitments; please refer to Sheldon Brown for information about older bikes.
A freehub is a part of the rear bicycle hub and serves two key functions. Firstly, it performs the ratcheting duty, allowing the cassette to stay stationary while the rest of the hub can spin freely so you can coast. Secondly, a freehub is what the cassette (rear gear sprockets) is attached to. This article focuses on the attachment function of a freehub; the ratcheting purpose is covered in a previous feature about freehub ratchet mechanisms.
It’s important to note the difference between freehubs (what this article covers) and freewheels. Both allow the bike to coast, but a freehub provides the ratcheting mechanism as part of the rear hub, while freewheels integrate that mechanism into the rear sprockets, which are then threaded on to the rear hub. If you have a bike from the past 20-30 years with more than eight gears in the back, it’s almost certain that you’ll have a freehub. BMXs, single-gear, entry-level adult, and kids bikes may still feature freewheels.
If you’re unsure whether your bike features a freehub or freewheel, then take a look at the rear sprockets and give them a backward spin. On a cassette and freehub system, the lockring spline at the end of the cassette will move with the sprockets when they’re spun backward. On a freewheel system, that spline will remain stationary when the sprockets are spun backward. Park Tool offers a good guide for differences between freehubs and freewheels.
Mixing and matching freehubs
While this article covers the types of external spline fitments available on freehubs, it’s critical to note that each brand and model of rear hub is likely to use its own proprietary freehub. If you’re looking to change a freehub body, then you’ll need to find out specifically what brand, model, and even generation of rear hub you have and what spare parts are available for it.
Freehub bodies are almost always replaceable, but not all hub/wheel brands offer all types of freehub bodies. For example, Shimano wheels are typically locked into the style of freehub body they were initially supplied with, and the company doesn’t offer replacement freehub bodies for use with Campagnolo or newer SRAM cassettes. Meanwhile, most other hub brands (depending on the age) offer the ability to change the freehub body fitment type.
Some brands are truly great at offering various different freehub body fitments to suit all of the latest drivetrain styles. For example, DT Swiss offers freehub bodies that cater to all current popular drivetrain demands, and (partly) as a result, a number of wheel brands choose to use DT Swiss hub internals.
Types of freehub body fitments
Below is a list of the most commonly found freehub bodies on the market today.
Shimano HG – Original/Mountain type
Shimano’s Hyperglide (HG) freehub design has been around since 1990 and remains the most common option in use today. It is now commonly referred to as an “HG Mountain” freehub body and offers a nine-spline design, with a single wider (keyed) slot that aligns the individual pieces of the cassette. The approximate 34 mm diameter across the splines means that an 11T sprocket is the smallest that can be fitted to this style of freehub body.
At (approx) 35 mm across the spline length, the original-width HG freehub remains current for mountain bike purposes, but is discontinued on road-specific wheels. This freehub fits 7, 8 and 9-speed Shimano and SRAM cassettes, regardless of whether the cassettes are for road or mountain biking.
Shimano 10, 11, and some 12-speed (if the smallest sprocket is 11T or greater) mountain bike cassettes are also a direct fit. Likewise, SRAM 10, 11, and some 12-speed (also with an 11T smallest sprocket) mountain bike cassettes fit. These newer 11 and 12-speed mountain bike cassettes fit the older and narrower HG freehub body by cantilevering the biggest cogs over the spokes.
Things are more complicated with newer road drivetrains. Shimano 10-speed road cassettes fit with the addition of a small 1 mm spacer behind the cassette (which is usually supplied, except for Tiagra cassettes where it is not required). SRAM 10-speed road cassettes are a direct fit without the need for such a spacer.
Shimano HG 11 (Shimano 11-speed)
The introduction of 11-speed road cassettes required a new freehub with the same spline pattern as Shimano HG, but an extra 1.85 mm of length to accommodate the additional sprocket (now measuring 36.85 mm). This is commonly just called “Shimano 11” or “HG 11”. Both Shimano and SRAM 11-speed road cassettes require this longer 11-speed freehub body. Similarly, new Shimano 12-speed road cassettes will fit HG 11 freehubs.
With the addition of a 1.85 mm washer behind the cassette, the 11-speed freehub bodies are backward compatible with the full list of cassettes covered above in “HG Mountain.”
There are four stipulations of note relevant to HG and HG 11 freehubs. Firstly, there was a short time frame (roughly 2004-2007) where Shimano introduced a 10-speed road-specific freehub design with a shorter body and deeper splines, in an effort to both reduce the chance of the cassette cutting into the freehub body and to increase the spoke flange distance. This freehub body design was quickly discontinued and should only be found on a few series of old high-end Shimano wheels/hubs. Unless modified, these defunct freehub bodies are locked into Shimano 10-speed road cassettes only. This is also why most Shimano 10-speed road cassettes are provided with a thin 1 mm spacer that must be used with regular freehub bodies (spacer goes behind the cassette, always).
The second stipulation is that Shimano’s 11-speed 11-34T “road” cassettes are actually rebadged mountain bike cassettes, which means they will fit on older 8-10-speed freehubs. This means that you can often use one of these 11-speed cassettes on either a mountain bike wheel or an older road wheel. These cassettes require the use of a 1.85mm spacer (supplied) to fit on an 11-speed Road HG freehub. By comparison, SRAM’s 11-36T 11-speed cassettes (PG-1170) are a pure road product and therefore require an HG-11 freehub body.
The third fun fact is that Shimano HG freehubs on older Mavic hubs are approximately 36.75 mm in length, and therefore previously required the use of a 1.75mm spacer for 10-speed or older cassettes. This means that many older pre-11-speed Mavic freehubs are ready to accept everything from 8-12 speed HG-fitment cassettes, including 11 and 12-speed Shimano road.
And the fourth stipulation is in regards to 6 and 7-speed HG-style cassettes and freehub bodies. Both 6 and 7-speed HG cassettes are narrower in width and therefore can be installed on any of the above HG freehub bodies with the addition of a 4.5 mm spacer behind the cassette. However, newer 8, 9, 10, 11 and 12-speed cassettes cannot be fitted to old and narrower 7-speed freehub bodies.
Introduced with XTR 12 speed, Microspline is Shimano’s answer to fitting a smaller 10T sprocket onto a freehub body. This 23-spline freehub body is noticeably shorter in length (26 mm) than an HG body and uses cassettes that hang the smaller sprockets over the end of the freehub.
Shimano Microspline freehub bodies are only compatible with Shimano 11 and 12-speed mountain bike cassettes that feature a 10T smallest sprocket. These wide-range cassettes will not fit any other freehub body, and similarly, no other cassette design (including Shimano 12-speed road) will fit a Microspline freehub body. Put another way, if you have a Shimano cassette with a 10T smallest sprocket, then you’ll require a Microspline freehub body.
Options for Microspline freehub bodies are steadily increasing and are currently available to suit hubs/wheels from Shimano, DT Swiss, Hope, Bontrager, Stan’s NoTubes, Industry Nine, and more. Similarly, the likes of Garbaruk are now offering Microspline cassettes.
Shimano EV Road
Oh but wait, there’s more. With the introduction of its new 12-speed road groupsets, Shimano also announced a new spline pattern specific to its new road cassettes. However, this new spline pattern is not required to use the new 12-speed cassettes.
Shimano 12-speed road cassettes remain backward compatible with common Shimano 11-speed HG freehub bodies. Meanwhile, the new 12-speed road-specific EV freehub simply adds more splines to better spread the load area of the cassette and reduce the risk of the cassette biting into the softer aluminium material.
Shimano EV freehub bodies are only compatible with Shimano 12-speed road cassettes. Shimano 12-speed mountain bike cassettes are not compatible, either. At this time, only Shimano is offering the EV Road freehub, while all other brands are instead continuing to offer the vastly more widely compatible and easier-to-manufacture HG11 design.
SRAM’s XD freehub body was created to fit SRAM’s own wider range mountain bike cassettes, which feature a smaller 10T sprocket; pre-existing freehub body designs couldn’t handle anything smaller than an 11T one. The XD system uses a one-piece cassette design that features a securing thread at the back of the freehub body.
SRAM XD freehub bodies will only work with SRAM 11 and 12-speed mountain bike cassettes that feature a 10T smallest sprocket (this includes the 10-42T 11-speed cassettes marketed for gravel and cyclocross use). All SRAM cassettes that feature an 11T smallest sprocket will require an HG freehub body.
SRAM intended the design to be easily adaptable to most existing hub designs, and as a result, just about every major hub manufacturer offers an XD-compatible freehub. The one exception to this is Shimano, who to this day has never produced an XD freehub body for its own wheels or hubs.
Cassette removal and installation tools required for SRAM XD are identical to those used for Shimano HG, Microspline and EV-style freehub bodies. Props to SRAM for keeping this consistent.
SRAM XDR is the latest version of SRAM XD, and is simply 1.85 mm wider than the original (just like HG vs HG 11). An XDR freehub body is required to fit 12-speed SRAM Road AXS and XPLR cassettes.
Narrower SRAM XD cassettes designed for a regular XD freehub can be fitted to an XDR body with the use of a 1.85 mm spacer behind the cassette. This is the identical size spacer that is used for spacing down Shimano HG 11 freehubs – even the splines match.
Campagnolo has long used its own tall-spline freehub variant, something that in its current iteration dates back to its introduction of 9-speed gearing. Impressively, the Campagnolo freehub body has remained relevant to this day and is compatible with all Campagnolo cassettes ranging from 9 through to 12-speed. Campagnolo deserves big points for such component fitment longevity.
Do note that Campagnolo uses its own lockring tool interface and so a Campagnolo-compatible tool will be required for swapping cassettes. Similarly, the cassette is held by a unique size lockring that is not cross-compatible with HG-style cassettes. Also, note that old 8-speed Campagnolo cassettes use a different freehub system and are not a direct fit for the existing Campagnolo freehub design.
Like Shimano’s HG freehub, Campagnolo’s freehub was also limited to an 11T sprocket as the smallest size. And so Campagnolo’s entry into the 1x-specific gravel space with 13-speed Ekar brought along a new and shorter freehub body design that created room for a smaller 9T sprocket.
The N3W freehub body features the same spline pattern as Campagnolo’s previous freehub, but is 4.4mm shorter in length. In its stock format, only Campagnolo Ekar 13-speed cassettes can fit an N3W freehub. Similarly, Campagnolo Ekar 13-speed cassettes require the use of an N3W freehub.
Campagnolo also offers an adapter kit (#AC21-N3W) that allows older 9-12-speed Campagnolo cassettes to fit an N3W freehub. The lockring tool for N3W cassettes is the same as regular Campagnolo cassettes, though the lockring itself is unique to the adapter kit.
The availability of N3W-compatible wheels is improving all the time. Currently, Campagnolo, Fulcrum, DT Swiss, Mavic, FFWD, Hunt, and a number of others cater for the new design. And as a reminder, there are a number of wheel companies that employ DT Swiss rear hub internals that could be changed to an N3W freehub.
Diagnosing what cassette type you have
Need to know what freehub body your wheel has but don’t want to remove the cassette to find out? This guide will help, but be warned that incorrectly counting or misreading something will easily result in you ordering the wrong part. Similarly, selecting a freehub body for a particular wheel or rear hub can require a high level of technical knowledge. And on a related note, many wheel brands consider freehub bodies to be a service component that can only be purchased through an approved retailer – sometimes, these things aren’t so easily sourced online. If in doubt, consult your local bike store (or ideally the source of the wheel in question).
The first step is to count your cassette’s number of sprockets (gears). This will likely be a number between 8 and 12.
Next, count how many teeth the smallest sprocket offers. Is it 9, 10, 11, 12, or even bigger? Remember that a 10T or smaller indicates a newer style of freehub (Microspline, XD/XDR, or N3W) is required.
Now look for a lockring holding the cassette. Does it offer any branding? Alternatively, look on the cassette (often visible from the back) for a brand and/or model.
While rare, you should also beware of outliers. For example, e-thirteen, Sunrace, and a few other brands offer cassettes that take a unique fitment approach to work with pre-existing freehub designs.
And lastly, you may consider avoiding the need for a new freehub or cassette by mixing and matching drivetrain components. Mixing and matching components is an endless topic as drivetrain manufacturers continue to progress their respective technologies.