A 9-speed chain can be used on a single-speed bike but only when the chainring is of the correct width for the chain.
A narrow-wide chainring or one taken from a multi-speed bike will work.
A dedicated single-speed chainring, however, is too thick and incompatible with multi-speed chains.
Compatibility Factors
The factors that determine the compatibility between a 9-speed chain and single-speed drivetrains are:
- Chain inner width
- Chainring thickness
- Rear cog thickness
Chain Width
Chains have two widths – inner and outer.
As one might expect, the inner width is the distance between the inner plates whereas the outer width is the distance between the external plates (image below).
The inner chain width depends on the thickness of the rear cogs and the chainrings. From 9 to 12 speeds, the inner chain width doesn’t change because neither does the thickness of the cassette sprockets.
The outer width of a chain decreases with each gear increase as cassettes designed for more speeds are “denser” and thus have smaller spacing between the sprockets. If the outer width of the chain remained the same, the external plates would rub against the cogs surrounding them.
The outer width of a chain is not relevant in this particular compatibility issue because there isn’t a cassette (unless the user decides to use a cassette for the conversion rather than a single cog for financial or stylistic reasons).
In this case, we have to focus on the inner width of the chain.
The table below contains the inner and outer widths of multi-speed chains:
| 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 |
The inner width of a 9-speed chain is 2.18mm. Consequently, the chain can be used only with a chainring and rear cog that are notably thinner than 2.18mm, preferably under 2mm.
The ideal options are an 8/9/10/11/12-speed chainring or a narrow-wide chainring.
The narrow-wide chainring is a more logical choice as it’s engineered to improve chain retention on 1x drivetrains via teeth of alternating width – one is narrow, and the next is wide (hence the name).
This pattern is specifically chosen to match the varying width of a chain.
The wide teeth slide between the outer plates whereas the narrow ones go between the inner plates.
As a result, the chain is less likely to drop.
Most narrow-wide chainrings are compatible with 9/10/11/12-speed chains (read more).
FAQ: Can I use a dedicated single-speed chainring and cog?
No. The thickness of the average single-speed chainring is 2mm or more because the inner width of single-speed chains is 1/8″ (3.3mm). Therefore, a 9-speed chain is too narrow for a single-speed chainring.
A Note On Chain Tension
Since you’re asking about using a 9-speed chain for a single-speed conversion, chances are that you’re trying to convert a multi-speed bike to a single-speed unit.
In that case, chain tension could be an issue. Normally, the rear derailleur tensions the chains dynamically regardless of the gear. However, a single-speed bike doesn’t have a rear derailleur.
The absence of a rear derailleur could create a problem if the bike has vertical dropouts.
Vertical dropouts make it impossible to tension the chain. In that scenario, you have to keep the original derailleur or install a dedicated chain tensioner. Otherwise, there isn’t an effective way to set the chain tension.
If the bike has horizontal dropouts, you can tension the chain by pulling the wheel backward. A tensioner won’t be needed in that situation.
