Are 8 and 9 Speed Cassettes the Same Width?

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Bike component manufacturers come up with new components with new specifications every now and therefore, the market is full of various options. 

A wide variety of products makes confuses you, especially when the manufacturers some parts aren’t compatible with other components of your bike. Whether you are a pro-level biker or a beginner, it becomes difficult to decide.

This is why cyclists need to know even the minor details of the bike’s components as it helps to maintain the bike nicely.

Same width, different spacing

When it comes to bike parts, one of the most confusing things is cassettes, especially since these come with different speeds. Here are some details for you to know when you’re thinking about whether you should get an 8-speed or a 9-speed cassette for your bike:

  • Both 8-speed and 9-speed have the same freehub width, while the 7-speed is a bit narrower.
  • The spacing of gears of 8-speed and 9-speed differ.
  • You need a spacer behind a 7-speed cassette for it to fit on an 8-speed or 9-speed freehub.

The cogs of these cassettes have the same width, although the spacing varies. This means that a 9-speed chain could work adequately with an 8-speed cassette. 

This is also the reason why 9-speed chains aren’t very durable. The outer width is a bit narrower, while the inner width is the same. This means that the plates on the chain are a bit weaker and thinner.

Sometimes, the difference lies in the brand

Sometimes, the difference lies in the brand. For instance, the 8-speed cassettes of the Campagnolo and Shimana brands don’t have the same spacing. This means that it’s quite challenging to get good indexing when you use an 8-speed wheel from Campagnolo with a cassette from Shimano, and vice-versa.

For the Shimano brand, their 9-speed cassettes have an extra cog added to the 8-speed cassette, while the overall width remains the same. It has a reduced gap between the gears and as such, it requires a narrower chain. The same thing goes for the 10-speed where it still has the same width as an 8-speed cassette. This makes the 10-speed slightly narrower.

For the speed systems in the 7, 9, and 10, the sprocket spacing of different brands doesn’t differ significantly, so it doesn’t cause many difficulties when used. To ensure a perfect match, you can do the following: 

  • Substitute your spacers
  • Use alternative cable routing
  • Use a special pulley adaptor

Estimated widths of different bike components

The width of the cassette you need for your bike also depends upon its compatibility with the other parts. Depending on what you need, you may want to consider researching the specific cassette you plan to buy as the values might vary slightly. To give you some idea of the measurements of different bike components, here are some estimates:

  • For Spacer Width: 8 Speed (3.00mm), 9 Speed (2.56mm)
  • For Cog or Tooth Width: 8 Speed (1.8mm), 9 Speed (1.78mm)
  • For Chain Width: 8 speed (7.1mm), 9 speed (6.6 to 6.8mm)

Other things to consider when looking for speed cassettes

Along with compatibility, you may also want to look into the dropout spacing at the rear. For example, if you have a 126mm bike, you should know that 8-speed and 9-speed need 130mm. 

Additionally, if your bike has a frame made of aluminum, some people would warn you against the stress caused should you use a wider wheel. As such, you may need a new chain, new shifters, and maybe even a new derailleur on the rear.


The 8-speed and 9-speed, even the 10-speed cassettes can all fit in the same hub. This simply means that if your bike is an older model with 8 gears on the rear, you may opt for an 8, 9, or 10-speed without needing to change your bike’s rear wheel. The reverse way works too. 

With this information on-hand, the next thing you may want to consider is the need, if any, and the compatibility when changing other components of your bike. Research everything that you need to know before starting to work on your bike for the purpose of maintenance. Do this to lessen your risk of facing issues. 

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