Condensed Answer:
A 12-speed chain and an 8-speed cassette are NOT an ideal combination.
The chain is too narrow internally and externally to operate sufficiently well with an 8-speed cassette. The user is likely to experience delayed shifting (latency) and issues with the chainrings and cogs.
If you have an 8-speed cassette, it’s better to pair it with a 7/8/9-speed chain.
If you have a standard 12-speed chain, it’s compatible with 11/12-speed cassettes.
Some 12-speed chains can only be paired with a 12-speed cassette from the same family. (e.g., Shimano Micro Spline).
Why Are 12-speed Chains and 8-speed Cassette Incompatible?
It comes down to dimensions.
Chains have an inner and outer width. The inner width is the distance between the inner plates; the outer width is the distance between the external plates.
Both the inner and the outer width are dependent on the number of gears that the bicycle is designed for.
The inner width doesn’t change much with each gear increase or decrease because it has to reflect the thickness of the cogs.
The outer width, however, changes with each gear increase/decrease.
More gears = narrower outer width; Fewer gears = extra width.
Why?
As the number of speeds increases, cassette cogs get closer to one another to preserve the overall width of the cassette the same. The goal is to make the hubs compatible with multiple cassettes. Hence the possibility to install an 11-speed cassette on a 10-speed hub, for example.
The decreased cog pitch (center-to-center distance between two cogs) requires a thinner chain to prevent rubbing between the chain’s outer plates and the cogs. This is achieved by thinning out the outer plates since the inner chain width doesn’t change much.
As a result, 12-speed chains are notably thinner than 8-speed chains.
The tables below contain the inner and outer width of multi-speed chains as well as the cog-pitch and the sprocket thickness of various 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 |
| Number of Speeds | Cog Pitch | Sprocket Thickness |
| 8 | 4.8mm | 1.85mm |
| 9 | 4.35mm | 1.78mm |
| 10 | 3.95mm | 1.6mm |
| 11 | 3.9mm | 1.6mm |
| 12 | 3.55mm | 1.6mm |
Conclusions:
- 12-speed chains are 0.2mm narrower internally than 8-speed chains
- 12-speed chains are 2mm narrower externally than 8-speed chains
- 8-speed sprockets are 0.25mm thicker than 12-speed ones
Those dimensions create the following issues:
- 8-speed sprockets and chainrings could cause some binding due to the narrower internal width. In other words, there simply isn’t enough space for the sprocket/chainring to feel free. The chain will lose its flexibility and that will be reflected by the shifting performance.
- The rear derailleur has to travel approximately 2mm extra to reach the chain and move it onto the next cog. The result is poor and delayed shifting.
What should I do?
Option 1: You are on a “deserted island”.
If you are on a tour and your chain breaks and becomes unusable and your only option is a 12-speed chain (a highly unlikely scenario), it makes sense to use it to get home or to wherever you’re going.
To avoid the negative downsides mentioned above, limit the shifting that you do, especially in “high adrenaline” situations.
Once you have access to a 7/8/9 speed chain install it on the bike.
That said, the scenario above is highly unlikely because 7/8/9 speed chains are much more common than 12-speed models, especially in developing countries.
Option 2: You bought the wrong parts.
Just return the chain and get an 8-speed model. If you can’t due to the absence of a receipt, buy a new 8-speed chain. They’re fairly cheap (any brand will do).
Related Questions and Topics
Can I use an 8-speed chain on a 12-speed cassette?
8-speed chains are too wide for 12-speed cassettes. The chain would rub against the adjacent cogs and the shifting experience would be poor, to say the least. If you have a 12-speed cassette, your only option is a 12-speed chain.
Some 12-speed lines like Shimano Micro Spline are designed to operate only with 12-speed chains from the family due to their unique architecture facilitating shifting.
Are 8-speed chains stronger than 12-speed chains?
When all parameters are equal (quality, conditions…etc.), chains designed for fewer speeds are stronger thanks to their thickness. Single-speed chains are the thickest and the strongest of them all.
Can you use an 11-speed chain on a 12-speed cassette?
An 11-speed chain will cause chain rubbing and poor shifting when used on a 12-speed cassette because of the extra width. If your goal is optimal shifting, it’s recommended to avoid this combination.
Also, an 11-speed chain will accelerate component wear due to the stress on the drivetrain.
Given how expensive and “spoiled” 12-speed components are, it makes no financial sense to experiment with parts from other group sets that “kinda work”. If you have already invested in a 12-speed system, it’s best to stick with it all the way.
