Freehub and freehub body: function, compatibilities and conversion

The freehub is nowadays (almost) unthinkable without the bicycle, as it makes life easier for many bikers. Some also appreciate it for its individual sound, which in some cases can even replace the bicycle bell. Incidentally, the bicycle freehub, as we know it to this day, was invented by Ernst Sachs in 1889 in one of the German bicycle metropolises: Schweinfurt. We explain here how the freehub works on your bike, what you should pay attention to when converting your gears and which freehub is compatible with which gear.

Pawl vs. Ratchet

Freehubs on bicycles are usually designed either with so-called pawls or as toothed disc freehubs. In a pawl freehub, form fit is produced with the help of coil springs. Two or more spring supports (pawls) are installed counter-clockwise in the freehub. When you pedal, they “lock” and the wheel turns. If you do not pedal, the pawls do not lock and the wheel runs freely. There are different operating principles as to how many pawls a freehub has, or how many of them can engage at the same time. The finer the ratchet of the pawl engagement, the smaller the engagement or disengagement angle. The idle travel of the crank decreases, and after rolling you have traction almost immediately again. This is especially important for time trial, mountain and gravel bikers. On a road or triathlon bike, where you are aiming for constant pedal rotation anyway, this is a less decisive factor. In this instance, fewer but larger pawls offer higher robustness and resistance against your leg force.
The second important design principle is the ratchet drive. DT Swiss and Shimano rely on ratchet drive in particular, as it promises low maintenance and a high degree of mechanical resilience. Following the expiration of a DT-Swiss patent in 2019, more and more ratchet designs are now coming onto the market. Here, two toothed pulleys are able to mesh with each other during pedalling. Unlike ratchet freewheels, toothed pulleys engage all teeth simultaneously. This ensures a very large contact area and makes freehubs very robust even with high force inputs. Small release angles, however, are not often possible.

Conversion: best without tools

How exactly the freehub body is converted varies between hub manufacturers. Many manufacturers like Hope, DT Swiss, SRAM or Shimano allow a tool-free conversion. You can find out ehether this is also possible for your hub in the operating manual or from our service team.

Materials: aluminium, steel, titanium

Freehub bodies are offered in various materials. Aluminium freehubs, for example, are quite light, but when used with (cassettes made of) single sprockets, they are susceptible to dents from kicks. With many cassettes, therefore, almost all sprockets sit on a carrier with full freehub width. Steel freehubs are more robust, but heavier. High-quality hubs sometimes come with freehub bodies made of titanium, which combine low weight and robustness.

Overview: The most common mounting standards

To help you keep perspective while shopping, we have briefly summarised and explained the most common mounting standards and cassette compatibilities. If you are in a hurry, jump directly to our overview table.

Shimano (Hyperglide) MTB

The Shimano Hyperglide MTB standard is suitable for 8- / 9- / 10- and 11-speed mountain bike cassettes from Shimano and various third-party manufacturers, where the smallest sprocket is eleven teeth or larger (including SRAM, but not SRAM XD or XDR).
Attention: Up to max. 10-speed versions can also be used with Shimano road-compatible cassettes.

Shimano Micro Spline

With a shift to 12-speed MTB drivetrains, Shimano has reintroduced the Micro Spline standard. It allows the smallest ten-tooth sprocket to be used, and is compatible with 12-speed MTB cassettes from Shimano as well as some third-party suppliers. Shimano licenses the use of Micro Spline technology to other rear hub or cassette manufacturers. This process ensures consistently high quality, but results in a relatively low number of options during the introductory phase of new technology.
Attention: Cannot be used with SRAM XD and XDR-compatible cassettes.

SRAM XDR

In contrast to SRAM XD, the XDR standard has a 1.85 mm larger intake. It is designed to use cassettes with a smallest sprocket of ten teeth or less and is compatible with SRAM road 12-speed cassettes. When using a 1.85 mm spacer, it is retroactively compatible with SRAM XD cassettes (see above).
Attention: Cannot be used with Shimano compatible cassettes.

Singlespeed/Fixie

For singlespeed and trial bikes, there are special hubs with narrow freehub bodies, which usually offer enough space to adjust the chainline with spacers. The narrow freehub allows for wider standing hub flanges, which enable the construction of more symmetrical and stiffer wheels. However, it limits the flexibility, because with such rear hubs a subsequent conversion to gears with cassette is not possible. On the other hand, you can convert freehub bodies for Shimano Road, MTB and SRAM (not XD or XDR) with appropriate spacers and singlespeed sprockets to single-speed operation. Singlespeed sprockets have a wide base to protect the freehub body.
On track bikes and fixies, the sprocket is screwed directly onto the hub body and secured with a counter-rotating ring. This prevents the sprocket from unscrewing itself from the hub without a freehub. With high quality track hubs such as those from Miche, the sprocket is placed on a carrier ring, making it easy to change ratios.
Occasionally, there are also singlespeed hubs with threading. For this type of construction, you need a sprocket with integrated freehub, i.e. a freehub pinion.

Table: Overview of compatibilities