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Here’s everything you want to know about freewheel bike, including how they work, gear ratio selection, materials, and more.
The vast majority of modern bicycles, whether mountain bikes, road bikes, or hybrid bikes, come equipped with a bike derailleur. The rear derailleur moves your chain up or down onto a set of freewheel cogs installed on the rear hub of your bike. These cogs (also known as gears or sprockets) make up your freewheel.
Freewheels come in various sizes to suit different purposes. The size of the freewheel is typically indicated by referencing the smallest and largest cog teeth counts. For example, a typical modern road bike freewheel might be an 11-32t (teeth) freewheel. For mountain bikes, the range could be 10-52t.
In this article, we’ll introduce what a freewheel is, how to identify its “speed,” explain typical gear ranges for different cycling areas, compare the main differences between low-cost and high-end freewheels, and more.
What is a freewheel?
A freewheel is a crucial part of most bicycle drivetrains. While it seems simple, a bicycle freewheel involves a lot of engineering. The multiple cogs within the freewheel are not just a set of gears but are designed to work together as a whole.
The individual cogs are precisely positioned to ensure the chain shifts smoothly between gears. The shape of each tooth on the cogs varies, and the sides of the cogs typically have ramps to assist with smooth transitions between gears. These shifting ramps are the result of years of refinement.
For example, Shimano uses a system called Hyperglide, designed to offer smooth shifting experiences. Their latest freewheels have been updated with Hyperglide+. According to Shimano, this system reduces shift time by a third and improves shifting performance under high loads compared to Hyperglide.
Other freewheel suppliers like SRAM and Campagnolo also have designs with similar functionality.
Freewheels are usually replaced as a whole. Since they are designed as a complete system, the cogs are sold as a set rather than individually. In most cases, you cannot just swap one cog for another with a different number of teeth, as it could affect shifting performance.
What is my freewheel's "speed"?
Freewheels can range from 7 to 13 cogs. Nowadays, it’s becoming more common to see high-end road bikes equipped with 12-speed drivetrains. After SRAM and Campagnolo both entered the 12-speed era, Shimano also joined the 12-speed road bike club in 2021 with its Dura-Ace Di2 R9200 group set.
For mountain bikes, a 12-speed freewheel is largely the default for mid-to-high-end setups, often paired with a single-chainring crankset. The number of cogs on your freewheel must match the speed rating of the other components. This is because almost all shifting systems are index-based, meaning the derailleur is designed to move a set distance with each shift.
Therefore, it won’t work with freewheels that have a different number of cogs because freewheels with more cogs have narrower chain spacing. The width of the chain must also match the number of cogs.
Generally, lower-end groupsets offer fewer gear ratios, and thus fewer cogs. However, there are exceptions: SRAM’s X01 DH and GX DH downhill mountain bike groupsets use a 7-speed freewheel compatible with an 11-speed chain. Fewer speeds allow for closer gear ratios per shift, which is better suited for bikes that don’t require climbing ability.
Gear ratios
In addition to the number of cogs, the range of teeth offered is a key determinant of compatibility between your freewheel and your drivetrain. Generally, freewheels start with 10, 11, or 12 teeth.
There are exceptions, with some options offering a 9, 13, or 14-tooth smallest cog. You may also see brands represent their freewheels’ range in terms of percentage.
For example, SRAM’s 10-52t freewheel offers a 520% gear range. How did SRAM arrive at this number? How do you calculate your gear range percentage?
Simply put, the smallest cog has 10 teeth, and the largest cog has 52 teeth, which is 520% of the 10-tooth gear. Therefore, the gear range is 520%. It’s important to note that this number only represents the gear range on the freewheel and doesn’t necessarily indicate that the same percentage will translate into riding distance.
It also won’t tell you if it’s suitable for your riding style. For that, you need to calculate the actual bicycle gear ratios, which is another topic altogether.
Road bike freewheels
In recent years, road bike freewheels have rapidly increased in size. A few years ago, an 11-28 was considered a “low-resistance” training freewheel, but now Shimano’s Dura-Ace R9200 offers 11-28 as the smallest option.
This may not sound like much, but considering that professional riders used to typically ride with 11-23 or 11-25 freewheels, this is a significant change.
This shift has been driven by the increase in freewheel speeds.
With 12-speed road bike groupsets now available, freewheels can have a wider range, while keeping the difference between each gear relatively small. For example, the smaller end of the freewheel might only differ by one tooth per shift, while the larger end will have greater jumps between cogs.
If you switched to a 7-speed or 8-speed freewheel but kept the same range, the gap between each gear would be larger.
Moreover, the industry’s attitude toward gearing has changed – grinding out big gears at low cadences is no longer seen as a sign of strength, much to the relief of our knees.
When Shimano and Campagnolo transitioned to 12-speed, they stuck with their existing gear ratios and used the extra cog to smooth out the gaps between the larger gears, so each shift feels closer. SRAM, however, took a different route (which we’ll explain shortly).
Shimano offers 11-28, 11-30, and 11-34 options with its latest R9200 groupset. These ratios were also available in Shimano’s 11-speed setups, though the Dura-Ace R9100 didn’t have the 11-34 option. Campagnolo offers an 11-29 option for all of its 12-speed groupsets, which was the largest freewheel available in its 11-speed range.
Now, the Italian brand offers an 11-32 option across the board. There’s also an 11-34 freewheel, but it’s only available for the Chorus-level groupset and supports only the Chorus rear derailleur.
Unlike Shimano and Campagnolo, SRAM revolutionized traditional gear ratios with its latest 12-speed AXS groupsets. They added a 12th cog to increase the gear range. SRAM road freewheels start with a smaller 10-tooth cog (requiring the use of an XDR freehub, which we’ll cover later).
SRAM also modified its chainring sizes, making them smaller than conventional sizes, offering 50/37 (only for Red), 48/35, and 46/33. By comparison, traditional chainring sizes are 53/39, 52/36, and 50/34. SRAM freewheels are available in 10-28 (Force and Red only), 10-30, 10-33, and 10-36.
Mountain bike freewheels
The size of mountain bike cassettes has also increased. This is primarily due to the emergence of 1x drivetrains, which lack a small chainring for climbing, meaning the cassette needs to provide a wider gear range to match appropriate climbing ratios.
Unlike road bikes, mountain bike cassette options are usually more limited.
Shimano only offers two cassette sizes in its 12-speed lineup – 10-45 (not available in the Deore range) and 10-51. The 10-51 option can only be used with a 1x setup, but the 10-45 can be used with both 1x and 2x systems.
SRAM’s Eagle series also offers just two cassette sizes – 10-50 and 10-52. The 10-52 is the largest cassette produced by any major component manufacturer. Although there are currently two choices, the 10-50 is likely to be phased out over time as it’s being replaced by the 10-52.
If you choose the 10-52 option, you need to ensure that you use a compatible rear derailleur, as the cage of the previous generation Eagle mechanical derailleurs is slightly shorter.
For users of SRAM’s two entry-level Eagle groupsets, SX Eagle and NX Eagle, SRAM offers an 11-50 cassette. This allows the cassette to fit onto a standard Shimano HG freehub body (more details on this later), as the 10t option requires the XD freehub.
SRAM has since released a new shifting system, which completely eliminates the derailleur hanger. The derailleur no longer has limit and fixing screws, so it only works with a 10-52t cassette.
Gravel bike freewheels
Gravel bikes are best seen as a hybrid between road and mountain bikes (XC bike vs. Gravel bike). Therefore, it’s normal to see them equipped with either road or mountain bike cassettes. However, as manufacturers have embraced gravel riding, dedicated gravel cassette options have become available.
SRAM’s XPLR AXS groupset is specifically designed for gravel riding. The SRAM XPLR cassette ranges from 10-44 and requires a specifically compatible rear derailleur. If you want an especially wide 1x range, you can also mix road handlebars with a mountain bike Eagle eTap AXS drivetrain. SRAM calls this the “mullet” setup. You can also mix XPLR AXS shifters and cranksets with the new Transmission drivetrain.
The latest SRAM Red XPLR AXS groupset is unique in that its rear derailleur attaches directly to the rear axle, similar to the Transmission mountain bike setup. What sets it apart from other SRAM cassettes is that it’s a 13-speed system with a 10-46t ratio.
Campagnolo is another manufacturer offering a 13-speed groupset for gravel riding. The Campagnolo Ekar 13-speed gravel groupset offers a cassette with a smallest sprocket of just 9 teeth. Cassette options include 9-36, 9-42, or 10-44. Ekar is a 1x-only groupset.
The slightly lower-tier Campagnolo Ekar GT groupset is also 1x, but with the option of a 10-48t cassette. Shimano GRX groupset users can choose a 10-45 or 10-51t cassette in a 12-speed 1x drivetrain, or 11-34 or 11-36t in a 2x combination.
For the initial 11-speed version, you could select one of Shimano’s own 11-speed road or mountain bike cassettes. Road cassettes max out at 11-34, while mountain bike cassettes offer 11-40, 11-42, or 11-46 options.
Shimano’s cassette range may seem more limited compared to its competitors, but it’s important to note that GRX is a gravel groupset compatible with both 1x and 2x systems.
Freewheel compatibility notes
Freehub compatibility
The freehub has splines that engage with the grooves on the cassette. These splines ensure the position between the cassette sprockets remains consistent and aligned, allowing the drivetrain to function properly.
Each drivetrain manufacturer has its own freehub design, meaning not all cassettes are compatible with every wheelset (or groupset).
Shimano freehub
The most common system is the Shimano 11-speed HG-style freehub, which has 9 splines. Until the 11-speed era, most Shimano groupsets used this style of freehub.
SRAM groupsets before the current 12-speed line also used the same freehub design, with a few exceptions, like SRAM’s 1×11 mountain groupsets. When Ultegra and Dura-Ace moved to 12-speed, Shimano also introduced a new freehub design for its road groupsets, although 12-speed Shimano cassettes are fully compatible with 11-speed freehubs.
On the mountain bike side, Shimano introduced a new freehub standard called Microspline to pair with its 12-speed Deore, SLX, XT, and XTR groupsets.
If you are using a Shimano HG freehub, you need to consider the width of the cassette you are purchasing. Road wheelsets’ freehubs are slightly wider (by 1.85 mm) than mountain bike wheelsets, and 11-speed Shimano HG road cassettes are also slightly wider than 8-speed or 9-speed cassettes, by the same margin of 1.85 mm.
You can add a 1.85 mm spacer to the inside of an 11-speed road hub to fit a lower-speed mountain or road cassette, but you cannot fit a road cassette on a mountain bike wheelset. Because 10-speed road cassettes are narrower than 8-speed or 9-speed ones, you’ll need a 1.85 mm spacer plus a 1 mm spacer to install it.
Campagnolo freehub
Campagnolo also has its own exclusive freehub specification, which is incompatible with either Shimano or SRAM products.
The brand has also introduced a new freehub standard called N3W to support its 13-speed Ekar cassettes. An adapter allows it to work with Campagnolo’s older standard cassettes.
SRAM freehub
When SRAM started offering cassettes with a 10-tooth smallest cog, they introduced the XD freehub standard. More recently, SRAM adapted this design for road bikes, introducing XDR, which allows road bikes to use 10t cassettes, though the standard is slightly wider than traditional road standards.
SRAM XDR road freehubs are 1.85 mm wider than SRAM XD MTB freehubs. Using spacers, you can install an XD cassette on a road wheelset with an XDR freehub, but you cannot use XDR cassettes on XD freehubs.
Mountain bike freewheels vs. road bike freewheels
Some people might want to use road cassettes on mountain bikes, or vice versa. Here, we’ll discuss why you may (or may not) want to do so, and examine the compatibility issues that may arise.
Most people won’t want to use road cassettes on mountain bikes. Traditional road cassettes have much narrower gear ranges than mountain bikes, and off-road riding requires a broader range to support technical climbing, while still offering small enough sprockets for descending.
Unless you’re using a triple crankset, you’re unlikely to want to use a road cassette on a mountain bike. If you’re still using a triple crankset, a road cassette might provide enough total range, but this is now a fairly “old-school” choice.
If you need a more climbing-friendly setup or you’re bikepacking, you might want to use a mountain bike cassette on a road bike. However, you need to ensure your freehub and derailleur are compatible with the larger cassette sprockets.
Derailleur cage design usually accommodates a specific range of sprockets. For example, Shimano’s Dura-Ace R9100-SS derailleur is designed to support a maximum cassette size of 11-30.
This means it’s incompatible with an 11-34 cassette because the derailleur cage isn’t long enough to provide sufficient chain (bicycle chain maintenance) tension when the derailleur is on the smallest sprocket, even though the chain must be long enough to accommodate the larger 34t cog.
If you want to use an 11-34t cassette on a road bike, you need a long-cage derailleur.
If you want to use an 11-34 cassette, in addition to buying the cassette itself, you’ll also need to purchase a compatible rear derailleur, such as Shimano’s Ultegra R8050-GS or 105 R7000-GS. GS indicates these are “medium cage” derailleurs.
The same naming rules apply to Shimano Di2 shifting. SRAM AXS derailleurs support a maximum of 33t road cassettes, typically indicated by “Max 33t” on the inside of the derailleur. There’s also a “Max 36t” option for pairing with 10-36 cassettes, and the XPLR derailleur can accommodate up to 44t (or the Red XPLR AXS with 10-46t cassettes).
Campagnolo 12-speed derailleurs support a maximum of 11-32. The only exception is the Campagnolo Chorus, which can accommodate up to 11-34.
If you’re upgrading to a cassette with a larger gear range, you also need to ensure your chain is long enough.
Flywheel materials: Steel vs. aluminum vs. titanium
The cheapest flywheels are usually made by die-casting steel, a material that is durable but heavy (Carbon fiber vs. aluminum wheel). As the price increases, you often get higher-end materials and more refined finishes.
For example, the top-tier Shimano Dura-Ace R9200 flywheel has 5 of its 12 cogs made from titanium alloy. The smaller cogs on the flywheel still use steel since they have fewer contact points with the chain. Softer materials would wear out faster.
SRAM, with its high-end SRAM Red AXS 12-speed road flywheel, uses a one-piece CNC machining process to remove excess material, thus reducing weight. Both Rotor and Miche reduce weight by making flywheels compatible with mainstream road bike groupsets out of aluminum alloy.
Larger cogs on a flywheel are often connected in groups and supported by a single bracket (often referred to as a “spider”), which engages with the freehub body.
This setup reduces weight, and since the bracket isn’t subject to chain wear, it can often be made from lighter materials – like the carbon fiber spider used on the Dura-Ace flywheel.
Some flywheels come with individual cogs. On mid-range flywheels, the cogs are usually separated by spacers, which can be made from alloy or sometimes plastic. Smaller cogs often come with integrated spacers.
Most flywheels (excluding SRAM XD and XDR) are fixed to the freehub body with a lockring (the flywheel cap), which is part of the entire flywheel assembly. The default material for lockrings is typically steel, but aluminum is a lighter alternative.
Flywheel prices: What do you get for your money?
You can spend a lot on high-end flywheels; some now cost over £300. So, what exactly are you paying for?
Higher-end flywheels are usually made from more unique materials, like titanium alloy or carbon fiber for some of the cogs and their brackets.
Others, like the SRAM Red road flywheel, are CNC-machined from a single piece. Generally, higher-end flywheels are more finely crafted and lighter than cheaper alternatives.
Besides weight, there isn’t a significant difference in performance between the Dura-Ace 11-28 flywheel and the flywheels in Shimano Ultegra or 105 groupsets, so you can save a lot by opting for a lower-tier flywheel.
SRAM offers similar choices, with the Rival eTap AXS introducing an entry-level 12-speed flywheel as a more affordable alternative to the Red and Force-level flywheels. The same logic applies to SRAM’s mountain bike groupsets.
It’s important to remember that flywheels are wear-and-tear components and need regular replacement.
If you typically replace your chain when the chain wear indicator shows 0.5 (for 11/12/13-speed) or 0.75 (for 10-speed and below), you can estimate your flywheel’s lifespan based on the rule of thumb that a flywheel can usually outlast three chains.
Some people’s flywheels may wear better, while others might wear faster. It all depends on how clean you keep your chain and your local riding conditions.
If you continue to use a flywheel with an overly worn chain, the flywheel will experience additional wear as the chain rollers elongate. Since replacing a high-end flywheel can be costly, it’s advisable to maintain your chain well to avoid unnecessary expenses.
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