Condensed Answer: A 10-speed chain can technically work with an 8-speed cassette, but the dimensions of the chain are not ideal. Both the inner and the outer width of the chain are shorter than those of a dedicated 8-speed chain.
Outer and Inner Chain Width
A bicycle chain has two widths – inner and outer.
The inner width is the distance between the inner points of the inner plates whereas the outer width is the distance between the outer points of the outer plates.
The Connection Between Chain Thickness and Cassette Width
The overall width of a cassette does not change much with each gear increase. The purpose of this engineering is to ensure that a rear hub can accept a large range of cassettes.
The dimensions of multi-speed cassettes are kept within tight tolerances via the following techniques:
- The sprockets get ever so slightly thinner with each gear increase. (The change is minimal.)
- The space between each cassette cog gets smaller with each jump. (Or in other words, more gears equal a denser cassette.)
Those above changes require modifications of the chain too.
As the number of gears climbs, the chain’s outer width decreases to avoid rubbing against the adjacent cogs.
In some cases, the inner width of the chain could also decrease slightly so that the chain can grab the slimmer cogs more effectively.
The table below contains the inner and outer width of 7-11-speed chains:
|Number of Speeds||Inner/Roller Width||Outer width||Sprocket Thickness|
|7||2.38mm||7.3mm (Shimano), 7.1mm (SRAM)||1.85mm|
|8||2.38mm||7.3mm (Shimano), 7.1mm (SRAM)||1.85mm|
The table reveals the following:
- The inner width of 8-speed chains is 2.38mm whereas that of 10-speed chains is 2.19mm (0.19mm difference).
- 8-speed sprockets are 1.85mm thick
The inner width difference between 8-speed and 10-speed cassettes is motivated by the different thicknesses of the sprockets.
The 2.38mm 8-speed chain provides more space for the 1.85mm sprockets found on 8-speed cassettes.
Meanwhile, the 2.18mm 10-speed chains eat the gap that would be formed if a chain of larger inner width is used in conjunction with 10-speed sprockets.
The 2.18mm inner width of 10-speed chains is sufficient for the 1.85mm thickness of 8-speed sprockets. The downside is the increased chance of chain binding, however. This outcome becomes even more likely when the chain and the cassette are dirty.
The Cons Of Combining a 10-speed Chain With an 8-Speed Cassette
10-speed chains are thinner and therefore not as strong as 8-speed models when all parameters (build quality…etc.) are equal.
- Slow and “weird” shifting
The ramps of the cogs will have a harder time picking up the chain due to its narrower profile. The shifting won’t be optimal and the rider may feel a delay between gear changes.
The components designed for 10,11 and 12-speed drivetrains tend to be more expensive than those made for 7,8 and 9-speed systems. Thus, there’s no financial incentive to purchase a 10-speed chain for an 8-speed cassette.
What Are the Advantages of Using a 10-speed Chain with an 8-Speed Cassette?
- Less Chain Rubbing
Obviously, an 8-speed chain is an optimal solution for an 8-speed cassette. If this wasn’t the case, there wouldn’t be a need to produce 8-speed chains.
That said, some people use 10-speed chains with cassettes designed for fewer speeds on purpose. The main goal is to reduce the rubbing of the chain against the front derailleur’s cage. (The 10-speed chain reduces the chances of rubbing because it’s slimmer.)
- Weight savings
10-speed chains require less material and are therefore lighter. The table below compares the weight of 10-speed and 8-speed chains.
|10-speed Chain||Weight||8-speed Chain||Weight|
|Shimano CN-6701||267g||Wippermann conneX 8sX||279g|
|KMC X10||268g||KMC X8||324g|
|SRAM PC 1051||277g||Shimano CN-HG71||324g|
|KMC X10EL||262g||SRAM PC 870||310g|
|Tiagra CN-4601||277g||SRAM PC 830||310g|
|Campagnolo Record||255g||Shimano CN-HG40||324g|
|KMC DLC10||257g||Wippermann conneX 8sE||308g|
Conclusion: On average, 8-speed chains are about 16% lighter. The difference in grams is minuscule and doesn’t matter unless one is trying to build the lightest possible bicycle.
A 10-speed chain tolerates cross-chaining better thanks to its additional flexibility. In some cases, it can give you an additional quick shift at the back before having to change the chainrings.
Summary: What You Need To Know
A 10-speed chain is not straight-up incompatible with an 8-speed cassette. Nonetheless, this combination can result in less than ideal shifting because 10-speed chains are significantly narrower than 8-speed models in total width.
The extra space that the narrower chain leaves could result in slow and somewhat inconsistent shifting.