Understanding Which Freehub 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 mean 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.

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.

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 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.

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.

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.

For us, the best recommendation for selecting a freehub for your wheels 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.

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)!