Condensed Answer: A 9-speed chain is too wide for a 10-speed cassette. The additional width will result in poor shifting, noise, and premature wear of the drivetrain.
It’s recommended to avoid this combination and go for a dedicated 10-speed chain. It’s also possible to use a chain designed for more than 10-speeds (e.g., an 11-speed chain).
Inner and Outer Chain Width
Bicycle chains have two widths – outer and inner. As the names suggest, the outer width is the distance between the external plates; the inner width is the distance between the inner plates.
The inner and outer width determine the cassettes that a chain is compatible with.
As the number of speeds on a cassette increases, the outer width of the chain has to decrease.
This engineering is necessary because the overall width of a cassette changes very little with each gear jump. Consequently, the only way to fit more cogs within roughly the same space is to decrease the so-called cog pitch. The cog pitch is the center-to-center distance between each sprocket.
To avoid rubbing of the chain’s outer plates against the cogs, the chain has to become thinner with each gear increase.
Because the thickness of each sprocket changes very little, the inner width of the chain remains the same across many cassettes.
Since the inner width cannot be changed, the only option left is to make the chain narrower by thinning out the outer plates.
For that reason, chains designed for more gears are considered weaker overall when all other parameters (material, craftmanship…etc.) are equal.
Below you will find the inner and outer width of 7 to 12-speed cassettes:
| Number of Speeds | Inner/Roller Width | Outer width |
| 7 | 2.38mm | 7.3mm (Shimano), 7.1mm (SRAM) |
| 8 | 2.38mm | 7.3mm (Shimano), 7.1mm (SRAM) |
| 9 | 2.18mm | 6.5-7mm |
| 10 | 2.18mm | 5.88-6mm |
| 11 | 2.18mm | 5.5-5.6mm |
| 12 | 2.18mm | 5.3mm |
Conclusions:
- The inner width of 9 and 10-speed chains is identical – 2.18mm.
- 10-speed chains are 0.5-1mm narrower in outer width.
Therefore, a 9-speed chain cannot be used on a 10-speed drivetrain without experiencing shifting issues, rubbing and drivetrain wear.
That said, if you have a “rat bike” of some sort that operates in single-speed more and happens to have a 10-speed cassette, a 9-speed chain won’t create nearly as many problems because there’s no shifting.
This is the only situation when a 9-speed chain on a 10-speed cassette can be partially justified.
FAQ: What about using a 10-speed chain on a 9-speed cassette?
A 10-speed chain has the same inner width as a 9-speed model while being narrower overall. Consequently, a 10-speed chain will not rub against the cogs that aren’t currently in use.
Therefore, the answer is yes – a 10-speed chain can operate fine on a 9-speed cassette. The only downside is that there could be a slight delay between the shifts due to the extra travel that the derailleur has to cover.
Ultimately, however, it’s highly questionable whether anyone can truly perceive that delay.
