Understanding Freehubs - Which One You Need & What They Are Used For

When FLO began in 2011, your choices of freehub were pretty simple: Shimano/SRAM or Campagnolo. Today, more freehub options means more questions. This article answers some of them: What is a freehub? What is its purpose? What kind of freehub do I have? It will also help you determine which option is best for you.

What Is A Freehub & What Is It Used For?


A freehub is the red part shown on the hub below, and are found only on rear hubs. It allows you to stop pedaling when you are riding a bike.

To see how that works, picture yourself on a bike:

Step 1: From a stop: Your feet are connected to the pedals, which drive the cranks, which drives the chain, which drives your rear wheel.

Step 2: Stop Pedaling at Speed Without a Freehub: When you stop pedaling, the whole system reverses itself; the momentum causes the wheel to become the driver, driving the chain, which drives the cranks, which drives your feet. On a bike that does not have a freehub on the rear wheel—known as a fixed gear bike (aka fixie) or single speed bike—you cannot stop pedaling until the bike stops. In order to stop, you have to resist the spinning of the cranks by pushing backwards.

Step 2 Stop Pedaling at Speed With a Freehub: When you stop pedaling, the freehub starts to spin, disengaging the chain from the rear wheel. This allows your chain, cranks, and—most importantly—your feet, to stay still.

Holding A Cassette

A second function of a freehub is to hold your rear cassette in place. The number of freehub options has increased as technological advances have increased, and many brands have begun making their own cassettes. Some examples:


Shimano and SRAM are two companies that make groupsets. The cassette—your gear cluster in the back—is a part of this groupset. In order to attach the cassette to the wheel, Shimano and SRAM use a key pattern that the cassette fits over, holding the cassette in place. The image below shows the key pattern for Shimano and SRAM cassettes.

This is a Shimano/SRAM cassette. You can see how it is made up of many gears, most individual pieces.

These pieces fit over the key pattern of the freehub. The image below shows the first piece on the freehub.

Campagnolo (aka Campy)

Campagnolo is another brand that makes groupsets for bicycles. Campy chose to use their own unique key pattern for their cassettes. You can see the key pattern below.

Below is a side-by-side shot of Shimano/SRAM and Campy cassette key patterns.

7, 8, 9, 10, & 11 Speed Cassettes

Over time, groupset manufacturers have added more and more gears to the cassette. If you go back many years, you will see 7-speed cassettes. Seven speed cassettes are still available on lower-end groupsets. Groupsets have progressed from 7 to 8, 8 to 9, 9 to 10, and now are 10 to 11 gears.

When FLO started and 11-speed was in its infancy, 10-speed and 11-speed freehubs were different. In order to add the additional gear on an 11 speed freehub, more space was added to the freehub.

The image below shows a 10 speed and 11 speed freehub side-by-side. You can see how the 11 speed freehub is deeper.

From a groupset perspective, you cannot interchangeably use the components from 10-speed and 11-speed groupset because the chain link size was changed. However, wheel manufacturers were smart and created a 1.8mm spacer that you can add to an 11-speed freehub. That spacer allows you to install a 10-speed cassette and run a 10-speed groupset, only now you can swap a wheel between a 10 and 11 speed bike simply by adding or removing a 1.8mm spacer, also known as a 10-speed spacer.

The image below shows a 10 speed spacer by itself and the second shows it installed on an 11-speed freehub.


A few years ago SRAM developed a new groupset that only uses one chain ring at the cranks.. As a result of only having one chain ring up front, much larger gears were used in the cassette, which completely redesigned the freehub. SRAM’s first iteration was XD, which held an 11 gear cassette. They later released the XDR, which holds a 12 gear cassette. The image below shows the key pattern of an XD & XDR freehub.

What’s important to note is that the installation is completely different. Instead of the cassette being many pieces, the cassette is one solid piece. The image below shows an XD cassette.

When installing an XD or XDR cassette, you have to thread the cassette in place compared to dropping it in place and tightening the cap. You can see the threads on the freehub in the picture below.

When SRAM added the 12th gear with XDR, they made a really good choice. Why? They created a 1.8mm space for the 12th gear which means the same 10-speed spacer used for converting a Shimano/SRAM 11-speed to 10-speed can be used to convert XDR to XD. That’s pretty cool.

Wheel Interchangeability

Hubs and freehubs come in all different shapes and sizes. How the freehub connects to the hub and how it operates mechanically are different for most hubs. For example, below is a freehub from our rim brake road line vs. a freehub from our disc brake road and gravel lines. While they are both XDR, the interface diameter is much larger for the gravel wheel line.

This is why it’s important to get a freehub that is compatible with your wheel. At FLO, Shimano/SRAM freehubs come standard, and you have the option to upgrade to Campy, XD, or XDR. Additionally, our accessories page has all freehub options for sale should you change your bike after your initial wheel purchase.

Choosing Your Freehub

For us, the best recommendation for selecting a freehub is to buy the latest freehub technology that matches your groupset, even if you don’t have the most recent one. For example, if you have a 10-speed Shimano/SRAM groupset, buy an 11-speed freehub. The same goes for XD & XDR; if you have an XD groupset, buy an XDR freehub. The 1.8 mm spacer allows you to have versatility should you upgrade your groupset in the future.

Knowing What Freehub You Need

So how do you know which freehub to choose at checkout? Choosing your freehub can be confusing at the checkout process if you’re not familiar so here are a few pointers:

  • Determine the brand: Locate the brand of your existing cassette—most likely it is Shimano, SRAM, or Campagnolo.
  • For a Campagnolo cassette, choose a Campy freehub.
  • For a Shimano freehub, count the number of gears on the cassette.
    • If you have 8, 9, 10, or 11 gears, select a Shimano/SRAM freehub.
  • For a SRAM freehub, count the number of gears.
    • If you have 10, select a Shimano/SRAM freehub.
    • If you have 12 gears, select an XDR freehub.
    • If you have 11, look at your crank.
    • If there is one chainring up front, select an XDR freehub.
    • If there are two or three chainrings (gears) up front, pick a Shimano/SRAM freehub.

If you’re still confused, call us. We’ll be happy to help!

We hope you found this article helpful. Happy freewheeling (unless of course you’re riding a fixie)!



The freehub stamped 1908 is for XDR. What wheel are you looking to replace the freehub on?

Ride safe,


Jon Thornham December 28, 2020

Hi Jon,

Could you send a link to the black Shimano 11spd freehub body shown in the picture and stamped with “1908” so I can purchase? My freehub body is a little chewed up and looks exactly the same as the one pictured. Thank you!

Will December 28, 2020


If the brand of the hub is Shimano, you will want a Shimano part. I would try searching the hub online for a replacement freehub or talking with a local bike shop.

Ride safe,


Jon Thornham November 18, 2020

Hi Flo, I am trying to replace my freehub body. It is a 3×7 speed mtb. Brand of rear hub is Shimano FH-MC 12 with 7 speed cassette.
how to I know which freehub body to buy on the internet to ensure compatibility?

Neo November 18, 2020


Your FLO 90 will have a red or black freehub. If it is red, you will need to upgrade it to an 11 speed freehub that you can find in our online ship under accessories. If it is black, then you will need to remove the spacers on the back of the cassette. This will allow you to install your 11 speed cassette and it will work. I hope this helps.

Take care,


Jon Thornham August 14, 2020

I have a FLO 90 with a 9 gear shimano. I would like to use it on my 11 gear DI 2. Can you retrofit or do I need another wheel.

Doug Butler August 11, 2020


The clicking noise come from the pawls engaging with the hub shell. There are many different designs. All include friction to some extent except maybe a few.

The amount of loss during costing is minimal. The best thing to do is to keep your legs moving.

You can reduce the noise by adding grease to the freehub internals. A dry hub will make more noise than a lubed one. I hope this helps.

Ride safe,


Jon Thornham August 04, 2020

Thanks Ben. I like this about Campy.

Jon Thornham August 04, 2020

Campagnolo freehubs have not changed as they moved through 9, 10, 11 & 12 speed. Cog spacing was reduced from 9 > 10 > 11; the cog itself is thinner for 12 speed.

Brian August 04, 2020

I purchased a set of roadbike wheels the slightly wider ones) from you a few years ago and all work well together. I have a Specialized Roubet. What has always baffled me is the shimano free hub the bike came with was quiet when freewheeling. But the free hub you provided makes the clicking noise. I always associate clicking with friction and therefore speed loss. What makes the clicking noise?

PS. I wrote to you with this same question but did not receive a response.

Ken Pearson August 04, 2020

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